BBA - Molecular Cell Research (v.1863, #6PA)
Editorial Board (i).
Overexpression of angiotensin II type 1 receptor in breast cancer cells induces epithelial–mesenchymal transition and promotes tumor growth and angiogenesis by Eunhye Oh; Ji Young Kim; Youngkwan Cho; Hyunsook An; Nahyun Lee; Hunho Jo; Changill Ban; Jae Hong Seo (1071-1081).
The angiotensin II type I receptor (AGTR1) has been implicated in diverse aspects of human disease, from the regulation of blood pressure and cardiovascular homeostasis to cancer progression. We sought to investigate the role of AGTR1 in cell proliferation, epithelial–mesenchymal transition (EMT), migration, invasion, angiogenesis and tumor growth in the breast cancer cell line MCF7. Stable overexpression of AGTR1 was associated with accelerated cell proliferation, concomitant with increased expression of survival factors including poly(ADP-ribose) polymerase (PARP) and X-linked inhibitor of apoptosis (XIAP), as well as extracellular signal-regulated kinase (ERK) activation. AGTR1-overexpressing MCF7 cells were more aggressive than their parent line, with significantly increased activity in migration and invasion assays. These observations were associated with changes in EMT markers, including reduced E-cadherin expression and increased p-Smad3, Smad4 and Snail levels. Treatment with the AGTR1 antagonist losartan attenuated these effects. AGTR1 overexpression also accelerated tumor growth and increased Ki-67 expression in a xenograft model. This was associated with increased tumor angiogenesis, as evidenced by a significant increase in microvessels in the intratumoral and peritumoral areas, and enhanced tumor invasion, with the latter response associated with increased EMT marker expression and matrix metallopeptidase 9 (MMP-9) upregulation. In vivo administration of losartan significantly reduced both tumor growth and angiogenesis. Our findings suggest that AGTR1 plays a significant role in tumor aggressiveness, and its inhibition may have therapeutic implications.
Keywords: Breast cancer; AGTR1; EMT; Losartan; Smad4; Angiogenesis;
Lovastatin protects keratinocytes from DNA damage-related pro-apoptotic stress responses stimulated by anticancer therapeutics by Verena Ziegler; Anne Albers; Gerhard Fritz (1082-1092).
Oral mucositis (OM) is a relevant adverse effect of anticancer therapy involving ionizing radiation (IR) and doxorubicin (Doxo). Because DNA damage of keratinocytes is causative for the pathogenesis of OM, we aim to identify pharmacological measures for geno- and cytoprotection of keratinocytes.We investigated the influence of the lipid-lowering drug lovastatin on cell death, proliferation and DNA damage response (DDR) mechanisms of human keratinocytes following treatment with IR and Doxo.Lovastatin protected keratinocytes from the cytotoxic and genotoxic effects of IR and Doxo as shown by a diminished induction of apoptosis as well as a reduced formation and slightly improved repair of DNA damage following Doxo and IR treatment, respectively. Lovastatin selectively blocked the activation of Chk1 and ATR kinases following treatment with IR, Doxo and the ribonucleotide reductase inhibitor hydroxyurea, indicating that the statin antagonizes ATR/Chk1-regulated replicative stress responses. Part of the cytoprotective activity of lovastatin seems to rest on a delayed entry of lovastatin treated cells into S-phase. Yet, because the statin also protected non-proliferating keratinocytes from IR- and Doxo-induced cytotoxicity, cell cycle independent protective mechanisms are involved, too.Lovastatin attenuates pro-toxic DNA damage-related responses of keratinocytes stimulated by OM-inducing anticancer therapeutics. The data encourage forthcoming in vivo and clinical studies addressing the usefulness of statins in the prevention of OM.
Keywords: Oral mucositis; Keratinocytes; Ionizing radiation; Anthracyclines; Statins; DNA damage response (DDR); DNA repair; Cell death;
RNA helicase Belle (DDX3) is essential for male germline stem cell maintenance and division in Drosophila by Alexei A. Kotov; Oxana M. Olenkina; Mikhail V. Kibanov; Ludmila V. Olenina (1093-1105).
The present study showed that RNA helicase Belle (DDX3) was required intrinsically for mitotic progression and survival of germline stem cells (GSCs) and spermatogonial cells in the Drosophila melanogaster testes. We found that deficiency of Belle in the male germline resulted in a strong germ cell loss phenotype. Early germ cells are lost through cell death, whereas somatic hub and cyst cell populations are maintained. The observed phenotype is related to that of the human Sertoli Cell-Only Syndrome caused by the loss of DBY (DDX3) expression in the human testes and results in a complete lack of germ cells with preservation of somatic Sertoli cells. We found the hallmarks of mitotic G2 delay in early germ cells of the larval testes of bel mutants. Both mitotic cyclins, A and B, are markedly reduced in the gonads of bel mutants. Transcription levels of cycB and cycA decrease significantly in the testes of hypomorph bel mutants. Overexpression of Cyclin B in the germline partially rescues germ cell survival, mitotic progression and fertility in the bel-RNAi knockdown testes. Taken together, these results suggest that a role of Belle in GSC maintenance and regulation of early germ cell divisions is associated with the expression control of mitotic cyclins.
Keywords: Belle (DDX3); Sertoli Cell-Only Syndrome; Testes; Germline stem cells; Drosophila; Cyclin B;
Pseudomonas aeruginosa lectin LecB inhibits tissue repair processes by triggering β-catenin degradation by Catherine Cott; Roland Thuenauer; Alessia Landi; Katja Kühn; Samuel Juillot; Anne Imberty; Josef Madl; Thorsten Eierhoff; Winfried Römer (1106-1118).
Pseudomonas aeruginosa is an opportunistic pathogen that induces severe lung infections such as ventilator-associated pneumonia and acute lung injury. Under these conditions, the bacterium diminishes epithelial integrity and inhibits tissue repair mechanisms, leading to persistent infections. Understanding the involved bacterial virulence factors and their mode of action is essential for the development of new therapeutic approaches.In our study we discovered a so far unknown effect of the P. aeruginosa lectin LecB on host cell physiology. LecB alone was sufficient to attenuate migration and proliferation of human lung epithelial cells and to induce transcriptional activity of NF-κB. These effects are characteristic of impaired tissue repair. Moreover, we found a strong degradation of β-catenin, which was partially recovered by the proteasome inhibitor lactacystin. In addition, LecB induced loss of cell–cell contacts and reduced expression of the β-catenin targets c-myc and cyclin D1. Blocking of LecB binding to host cell plasma membrane receptors by soluble l-fucose prevented these changes in host cell behavior and signaling, and thereby provides a powerful strategy to suppress LecB function.Our findings suggest that P. aeruginosa employs LecB as a virulence factor to induce β-catenin degradation, which then represses processes that are directly linked to tissue recovery.
Keywords: NF-κB; Wnt; Acute lung injury; Migration; Proliferation; Bacterial pathogenesis;
The effect of white light on normal and malignant murine melanocytes: A link between opsins, clock genes, and melanogenesis by L.V.M. de Assis; M.N. Moraes; S. da Silveira Cruz-Machado; A.M.L. Castrucci (1119-1133).
The skin possesses a photosensitive system comprised of opsins whose function is not fully understood, and clock genes which exert an important regulatory role in skin biology. Here, we evaluated the presence of opsins in normal (Melan-a cells) and malignant (B16–F10 cells) murine melanocytes. Both cell lines express Opn2, Opn4 – for the first time reported in these cell types – as well as S-opsin. OPN4 protein was found in a small area capping the cell nuclei of B16–F10 cells kept in constant dark (DD); twenty-four hours after the white light pulse (WLP), OPN4 was found in the cell membrane. Despite the fact that B16–F10 cells expressed less Opn2 and Opn4 than Melan-a cells, our data indicate that the malignant melanocytes exhibited increased photoresponsiveness. The clock gene machinery is also severely downregulated in B16–F10 cells as compared to Melan-a cells. Per1, Per2, and Bmal1 expression increased in B16–F10 cells in response to WLP. Although no response in clock gene expression to WLP was observed in Melan-a cells, gene correlational data suggest a minor effect of WLP. In contrast to opsins and clock genes, melanogenesis is significantly upregulated in malignant melanocytes in comparison to Melan-a cells. Tyrosinase expression increased after WLP only in B16–F10 cells; however no increase in melanin content after WLP was seen in either cell line. Our findings may prove useful in the treatment and the development of new pharmacological approaches of depigmentation diseases and skin cancer.Display Omitted
Keywords: Mouse; Melanocytes; Melanoma; Clock genes; Opsins; Cancer;
Protective effects of retinoid x receptors on retina pigment epithelium cells by Victoria Belén Ayala-Peña; Fiorella Pilotti; Yanel Volonté; Nora P. Rotstein; Luis E. Politi; Olga Lorena German (1134-1145).
Age-related macular degeneration (AMD) is among the main pathologies leading to blindness in adults and has currently no cure or effective treatment. Selective apoptosis of retina pigment epithelial (RPE) cells results in the progressive loss of photoreceptor neurons, with the consequent gradual vision loss. Oxidative stress plays an important role in this process. We have previously determined that activation of RXRs protects rat photoreceptor neurons from oxidative stress-induced apoptosis. In this study we investigated whether RXR ligands prevented apoptosis in an RPE cell line, D407 cells, exposed to hydrogen peroxide (H2O2). H2O2 induced apoptosis of D407 cells, promoting p65NFκB nuclear translocation, increasing Bax mRNA expression, activating caspase-3 and altering cell morphology. We show, for the first time, that HX630, a RXR pan-agonist, protected D407 cells from H2O2-induced apoptosis, preventing p65NFκB nuclear translocation, increasing Bclxl and PPARγ mRNA levels and simultaneously decreasing Bax mRNA levels and caspase-3 activation. Pretreatment with a RXR antagonist blocked HX630 protection. LG100754, which binds RXRs but only activates heterodimers and is an antagonist of RXR homodimers, also had a protective effect. In addition, only agonists known to bind to RXR/PPARγ were protective. As a whole, our results suggest that RXR activation protects RPE cells from oxidative stress-induced apoptosis and this protection might involve signaling through a heterodimeric receptor, such as RXR/PPARγ. These data also imply that RXR agonists might provide potential pharmacological tools for treating retina degenerative diseases.
Keywords: Retina pigment epithelium cells; Retinoid x receptors; Hydrogen peroxide; Oxidative stress; Peroxisome proliferator-activated receptor;
Pathologic endoplasmic reticulum stress induced by glucotoxic insults inhibits adipocyte differentiation and induces an inflammatory phenotype by Michele Longo; Rosa Spinelli; Vittoria D'Esposito; Federica Zatterale; Francesca Fiory; Cecilia Nigro; Gregory A. Raciti; Claudia Miele; Pietro Formisano; Francesco Beguinot; Bruno Di Jeso (1146-1156).
Adipocyte differentiation is critical in obesity. By controlling new adipocyte recruitment, adipogenesis contrasts adipocyte hypertrophy and its adverse consequences, such as insulin resistance. Contrasting data are present in literature on the effect of endoplasmic reticulum (ER) stress and subsequent unfolded protein response (UPR) on adipocyte differentiation, being reported to be either necessary or inhibitory. In this study, we sought to clarify the effect of ER stress and UPR on adipocyte differentiation.We have used two different cell lines, the widely used pre-adipocyte 3T3–L1 cells and a murine multipotent mesenchymal cell line, W20-17 cells. A strong ER stress activator, thapsigargin, and a pathologically relevant inducer of ER stress, glucosamine (GlcN), induced ER stress and UPR above those occurring in the absence of perturbation and inhibited adipocyte differentiation. Very low concentrations of 4-phenyl butyric acid (PBA, a chemical chaperone) inhibited only the overactivation of ER stress and UPR elicited by GlcN, leaving unaltered the part physiologically activated during differentiation, and reversed the inhibitory effect of GlcN on differentiation. In addition, GlcN stimulated proinflammatory cytokine release and PBA prevented these effects. An inhibitor of NF-kB also reversed the effects of GlcN on cytokine release. These results indicate that while ER stress and UPR activation is “physiologically” activated during adipocyte differentiation, the “pathologic” part of ER stress activation, secondary to a glucotoxic insult, inhibits differentiation. In addition, such a metabolic insult, causes a shift of the preadipocyte/adipocyte population towards a proinflammatory phenotype.Display Omitted
Keywords: Adipocyte differentiation; ER stress; Inflammation;
Epithelial membrane protein 2 regulates sphingosylphosphorylcholine-induced keratin 8 phosphorylation and reorganization: Changes of PP2A expression by interaction with alpha4 and caveolin-1 in lung cancer cells by Eun Ji Lee; Mi Kyung Park; Hyun Ji Kim; Eun Ji Kim; Gyeoung-Jin Kang; Hyun Jung Byun; Chang Hoon Lee (1157-1169).
Sphingosylphosphorylcholine (SPC) is found at increased in the malignant ascites of tumor patients and induces perinuclear reorganization of keratin 8 (K8) filaments that contribute to the viscoelasticity of metastatic cancer cells. However, the detailed mechanism of SPC-induced K8 phosphorylation and reorganization is not clear.We observed that SPC dose-dependently reduced the expression of epithelial membrane protein 2 (EMP2) in lung cancer cells. Then, we examined the role of EMP2 in SPC-induced phosphorylation and reorganization of K8 in lung cancer cells. We found that SPC concentration-dependently reduced EMP2 in A549, H1299, and other lung cancer cells. This was verified at the mRNA level by RT-PCR and real-time PCR (qPCR), and intracellular variation through confocal microscopy. EMP2 gene silencing and stable lung cancer cell lines established using EMP2 lentiviral shRNA induced K8 phosphorylation and reorganization. EMP2 overexpression reduced K8 phosphorylation and reorganization. We also observed that SPC-induced loss of EMP2 induces phosphorylation of JNK and ERK via reduced expression of protein phosphatase 2A (PP2A). Loss of EMP2 induces ubiquitination of protein phosphatase 2A (PP2A). SPC induced caveolin-1 (cav-1) expression and EEA1 endosome marker protein but not cav-2. SPC treatment enhanced the binding of cav-1 and PP2A and lowered binding of PP2A and alpha4. Gene silencing of EMP2 increased and gene silencing of cav-1 reduced migration of A549 lung cancer cells.Overall, these results suggest that SPC induces EMP2 down-regulation which reduces the PP2A via ubiquitination induced by cav-1, which sequestered alpha4, leading to the activation of ERK and JNK.Display Omitted
Keywords: Sphingosylphosphorylcholine; Epithelial membrane protein 2; Protein phosphatase 2A; Keratin 8 phosphorylation; Keratin 8 reorganization; Alpha 4;
Claudin-18 inhibits cell proliferation and motility mediated by inhibition of phosphorylation of PDK1 and Akt in human lung adenocarcinoma A549 cells by Shun Shimobaba; Saeko Taga; Risa Akizuki; Asami Hichino; Satoshi Endo; Toshiyuki Matsunaga; Ryo Watanabe; Masahiko Yamaguchi; Yasuhiro Yamazaki; Junko Sugatani; Akira Ikari (1170-1178).
Abnormal expression of claudin subtypes has been reported in various cancers. However, the pathological role of each claudin has not been clarified in detail. Claudin-18 was absent in human non-small cell and small cell lung cancers, although it is expressed in normal lung tissues. Here, we examined the effect of claudin-18 expression on the expression of junctional proteins, cell proliferation, and cell motility using human lung adenocarcinoma A549 cells. Real-time PCR and western blotting showed that exogenous expression of claudin-18 had no effect on the expression of junctional proteins including claudin-1, zonula occludens-1 (ZO-1), occludin, and E-cadherin. Claudin-18 was mainly distributed in cell–cell contact areas concomitant with ZO-1. Cell proliferation was significantly decreased at 48 and 72 h after seeding of claudin 18-expressing cells. Claudin-18 suppressed cell motility, whereas it increased cell death in anoikis. Claudin-18 decreased phosphorylated (p)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and p-Akt levels without affecting p-epidermal growth factor receptor and p-phosphatidylinositol-3 kinase (PI3K) levels. Furthermore, claudin-18 was bound with PDK1 and suppressed the nuclear localization of PDK1. We suggest that claudin-18 suppresses the abnormal proliferation and motility of lung epithelial cells mediated by inhibition of the PI3K/PDK1/Akt signaling pathway.Display Omitted
Keywords: Claudin-18; Lung cancer; Proliferation; Migration; PDK1;
Interaction with epsin 1 regulates the constitutive clathrin-dependent internalization of ErbB3 by Monika Szymanska; Anne Marthe Fosdahl; Camilla Raiborg; Markus Dietrich; Knut Liestøl; Espen Stang; Vibeke Bertelsen (1179-1188).
In contrast to other members of the EGF receptor family, ErbB3 is constitutively internalized in a clathrin-dependent manner. Previous studies have shown that ErbB3 does not interact with the coated pit localized adaptor complex 2 (AP-2), and that ErbB3 lacks two AP-2 interacting internalization signals identified in the EGF receptor. Several other clathrin-associated sorting proteins which may recruit cargo into coated pits have, however, been identified, and the study was performed to identify adaptors needed for constitutive internalization of ErbB3.A high-throughput siRNA screen was used to identify adaptor proteins needed for internalization of ErbB3. Upon knock-down of candidate proteins internalization of ErbB3 was identified using an antibody-based internalization assay combined with automatic fluorescence microscopy.Among 29 candidates only knock-down of epsin 1 turned out to inhibit ErbB3. Epsin 1 has ubiquitin interacting motifs (UIMs) and we show that ErbB3 interacts with an epsin 1 deletion mutant containing these UIMs. In support of an ErbB3-epsin 1 UIM dependent interaction, we show that ErbB3 is constitutively ubiquitinated, but that both ubiquitination and the ErbB3-epsin 1 interaction increase upon ligand binding.Altogether the results are consistent with a model whereby both constitutive and ligand-induced internalization of ErbB3 are regulated through interaction with epsin 1.Internalization is an important regulator of growth factor receptor mediated signaling and the current study identify mechanisms regulating plasma membrane turnover of ErbB3.Display Omitted
Keywords: ErbB3; Endocytosis; Clathrin; Epsin; Ubiquitin;
β-Amyloid induces nuclear protease-mediated lamin fragmentation independent of caspase activation by Vijay Sankar Ramasamy; Md. Imamul Islam; Md. Aminul Haque; Song Yub Shin; Il-Seon Park (1189-1199).
β-Amyloid (Aβ), a hallmark peptide of Alzheimer's disease, induces both caspase-dependent apoptosis and non-apoptotic cell death. In this study, we examined caspase-independent non-apoptotic cell death preceding caspase activation in Aβ42-treated cells. We first determined the optimal treatment conditions for inducing cell death without caspase activation and selected a double-treatment method involving the incubation of cells with Aβ42 for 4 and 6 h (4 + 6 h sample). We observed that levels of lamin A (LA) and lamin B (LB) were reduced in the 4 + 6 h samples. This reduction was decreased by treatment with suc-AAPF-CMK, an inhibitor of nuclear scaffold (NS) protease, but not by treatment with z-VAD-FMK, a pan-caspase inhibitor. In addition, suc-AAPF-CMK decreased the changes in nuclear morphology observed in cells in the 4 + 6 h samples, which were different from nuclear fragmentation observed in STS-treated cells. Furthermore, suc-AAPF-CMK inhibited cell death in the 4 + 6 h samples. LA and LB fragmentation occurred in the isolated nuclei and was also inhibited by suc-AAPF-CMK. Together, these data indicated that the fragmentation of LA and LB in the Aβ42-treated cells was induced by an NS protease, whose identity is not clearly determined yet. A correlation between Aβ42 toxicity and the lamin fragmentation by NS protease suggests that inhibition of the protease could be an effective method for controlling the pathological process of AD.
Keywords: β-amyloid; Alzheimer's disease; Nuclear scaffold protease; Lamin; Apoptosis; Caspase;
Rapamycin requires AMPK activity and p27 expression for promoting autophagy-dependent Tsc2-null cell survival by Tania Campos; Javiera Ziehe; Francisco Fuentes-Villalobos; Orlando Riquelme; Daniela Peña; Rodrigo Troncoso; Sergio Lavandero; Violeta Morin; Roxana Pincheira; Ariel F. Castro (1200-1207).
Tuberous sclerosis complex (TSC) disease results from inactivation of the TSC1 or TSC2 gene, and is characterized by benign tumors in several organs. Because TSC tumorigenesis correlates with hyperactivation of mTORC1, current therapies focus on mTORC1 inhibition with rapamycin or its analogs. Rapamycin-induced tumor shrinkage has been reported, but tumor recurrence occurs on withdrawal from rapamycin. Autophagy has been associated with development of TSC tumors and with tumor cell survival during rapamycin treatment. mTORC1 and AMPK directly inhibit and activate autophagy, respectively. AMPK is hyperactivated in TSC cells and tumors, and drives cytoplasmic sequestration of the cell-cycle inhibitor p27KIP (p27). Whether AMPK and p27 are involved in rapamycin-induced autophagy and survival of TSC cells remain unexplored. Here, we show that inhibition of AMPK by compound C or by shRNA-mediated depletion of LKB1 reduces activation of autophagy by rapamycin in Tsc2-null cells. Similarly, shRNA-mediated depletion of p27 inhibited rapamycin-induced autophagy. In support of p27 lying downstream of AMPK on the activation of autophagy in Tsc2-null cells, a p27 mutant that preferentially localizes in the cytosol recovered the effect of rapamycin on autophagy in both p27- and LKB1-depleted cells, but a nuclear p27 mutant was inactive. Finally, we show that p27-dependent activation of autophagy is involved in Tsc2-null cell survival under rapamycin treatment. These results indicate that an AMPK/p27 axis is promoting a survival mechanism that could explain in part the relapse of TSC tumors treated with rapamycin, exposing new avenues for designing more efficient treatments for TSC patients.
Keywords: Tuberous sclerosis complex; Rapamycin; AMPK; mTOR; p27; Cell survival;
The C-terminal domain controls the mobility of Crumbs 3 isoforms by Ivona Djuric; Jan Peter Siebrasse; Ulf Schulze; Daniel Granado; Marc A. Schlüter; Ulrich Kubitscheck; Hermann Pavenstädt; Thomas Weide (1208-1217).
The physiological function of epithelia depends on an asymmetric distribution of their membrane domains. Polarity proteins play a crucial role for distribution processes, however, little is known about their mobility in epithelial cells. In this study, we analyzed the intracellular and plasma-membrane-associated mobility of fluorescence-labeled Crb3A and Crb3B. Both variants belong to the Crumbs protein family, which control size and identity of apical membranes in epithelial cells. Fluorescence recovery after photo-bleaching measurements revealed different mobilities for the two Crb3 variants. They also differentially affected mobility and localization of the Pals1/Mpp5 protein, which binds to Crb3A but not to Crb3B. In addition, tracking of intracellular vesicles indicated that Crb3A containing vesicles are slightly more immobile than Crb3B ones. Taken together, our data revealed different intracellular mobility patterns for Crb3A and Crb3B.Display Omitted
Keywords: Crumbs; Crb; Crb3; Pals1; FRAP; Single particle tracking; Mobility; Cell polarity;
The role of interleukin-6 signaling in nervous tissue by Michelle Rothaug; Christoph Becker-Pauly; Stefan Rose-John (1218-1227).
The cytokine interleukin-6 (IL-6) plays a critical role in the pathogenesis of inflammatory disorders and in the physiological homeostasis of neural tissue. Profound neuropathological changes, such as multiple sclerosis (MS), Parkinson's and Alzheimer's disease are associated with increased IL-6 expression in brain. Increased nocturnal concentrations of serum IL-6 are found in patients with impaired sleep whereas IL-6-deficient mice spend more time in rapid eye movement sleep associated with dreaming. IL-6 is crucial in the differentiation of oligodendrocytes, regeneration of peripheral nerves and acts as a neurotrophic factor. It exerts its cellular effects through two distinct pathways which include the anti-inflammatory pathway involving the membrane-bound IL-6 receptor (IL-6R) expressed on selective cells, including microglia, in a process known as classical signaling that is also critical for bacterial defense. In classical signaling binding of IL-6 to the membrane-bound IL-6R activates the β-receptor glycoprotein 130 (gp130) and subsequent down-stream signaling. The alternative, rather pro-inflammatory pathway, shown to mediate neurodegeneration in mice, termed trans-signaling, depends on a soluble form of the IL-6R that is capable of binding IL-6 to stimulate a response on distal cells that express gp130. A naturally occurring soluble form of gp130 (sgp130) has been identified that can specifically bind and neutralize the IL-6R/IL-6 complex. Thus, trans-signaling is blocked but classical signaling is completely unaffected. A modified, recombinant dimerized version of sgp130 (sgp130Fc) has successfully been used to block inflammatory processes in mice and may also be used in the clarification of IL-6 trans-signaling in neurological diseases.
Keywords: IL-6 signaling; gp130; Multiple sclerosis; Sleep; Neurodegeneration; Trans-signaling;
A pepducin designed to modulate P2Y2R function interacts with FPR2 in human neutrophils and transfers ATP to an NADPH-oxidase-activating ligand through a receptor cross-talk mechanism by Michael Gabl; André Holdfeldt; Malene Winther; Tudor Oprea; Johan Bylund; Claes Dahlgren; Huamei Forsman (1228-1237).
Several G-protein-coupled receptors (GPCRs) can be activated or inhibited in a specific manner by membrane-permeable pepducins, which are short palmitoylated peptides with amino acid sequences identical to an intracellular domain of the receptor to be targeted. Unlike the endogenous P2Y2R agonist ATP, the P2Y2PalIC2 pepducin, which has an amino acid sequence corresponding to the second intracellular loop of the human ATP receptor (P2Y2R), activated the superoxide anion-generating NADPH-oxidase in neutrophils. In addition to having a direct effect on neutrophils, the P2Y2R pepducin converted naïve neutrophils to a primed state, which secondarily responded to ATP by producing superoxide. A pepducin with a peptide identical to the third intracellular loop of P2Y2R (P2Y2PalIC3) exhibited the same basic functions as P2Y2PalIC2, whereas one with a peptide that was identical to the first intracellular loop (P2Y2PalIC1) lacked these functions. The responses induced in neutrophils by the P2Y2R pepducins were not inhibited by the P2Y2R antagonist AR-C118925, and the receptor desensitization profile suggested the involvement of FPR2 rather than P2Y2R. Accordingly, antagonists/inhibitors of FPR2 attenuated the activities of the P2Y2R pepducins, which also selectively activated FPR2-overexpressing cells. In summary, we show that pepducins supposed to target P2Y2R activate human neutrophils through FPR2. We also show that the P2Y2PalIC2 pepducin can convert ATP from a non-activating agent to a potent neutrophil NADPH-oxidase activator. The molecular basis of this phenomenon involves cross-talk between the receptor/ligand pairs of P2Y2R/ATP and FPR2/P2Y2-pepducin.
Keywords: P2Y2R; Pepducins; FPRs; Neutrophils; Inflammation;
The molecular and cellular origin of human prostate cancer by John R. Packer; Norman J. Maitland (1238-1260).
Prostate cancer is the most commonly diagnosed male malignancy. Despite compelling epidemiology, there are no definitive aetiological clues linking development to frequency.Pre-malignancies such as proliferative inflammatory atrophy (PIA) and prostatic intraepithelial neoplasia (PIN) yield insights into the initiating events of prostate cancer, as they supply a background “field” for further transformation. An inflammatory aetiology, linked to recurrent prostatitis, and heterologous signalling from reactive stroma and infiltrating immune cells may result in cytokine addiction of cancer cells, including a tumour-initiating population also known as cancer stem cells (CSCs). In prostate tumours, the background mutational rate is rarely exceeded, but genetic change via profound sporadic chromosomal rearrangements results in copy number variations and aberrant gene expression.In cancer, dysfunctional differentiation is imposed upon the normal epithelial lineage, with disruption/disappearance of the basement membrane, loss of the contiguous basal cell layer and expansion of the luminal population. An initiating role for androgen receptor (AR) is attractive, due to the luminal phenotype of the tumours, but alternatively a pool of CSCs, which express little or no AR, has also been demonstrated. Indolent and aggressive tumours may also arise from different stem or progenitor cells.Castrate resistant prostate cancer (CRPC) remains the inevitable final stage of disease following treatment. Time-limited effectiveness of second-generation anti-androgens, and the appearance of an AR-neuroendocrine phenotype imply that metastatic disease is reliant upon the plasticity of the CSC population, and indeed CSC gene expression profiles are most closely related to those identified in CRPCs.Display Omitted
Chronic expression of Ski induces apoptosis and represses autophagy in cardiac myofibroblasts by Matthew R. Zeglinski; Jared J.L. Davies; Saeid Ghavami; Sunil G. Rattan; Andrew J. Halayko; Ian M.C. Dixon (1261-1268).
Inappropriate cardiac interstitial remodeling is mediated by activated phenoconverted myofibroblasts. The synthesis of matrix proteins by these cells is triggered by both chemical and mechanical stimuli. Ski is a repressor of TGFβ1/Smad signaling and has been described as possessing anti-fibrotic properties within the myocardium. We hypothesized that overexpression of Ski in myofibroblasts will induce an apoptotic response, which may either be supported or opposed by autophagic flux. We used primary myofibroblasts (activated fibroblasts) which were sourced from whole heart preparations that were only passaged once. We found that overexpression of Ski results in distinct morphological and biochemical changes within primary cardiac myofibroblasts associated with apoptosis. Ski treatment was associated with the expression of pro-apoptotic factors such as Bax, caspase-7, and -9. Our results indicate that Ski triggers a pro-death mechanism in primary rat cardiac myofibroblasts that is mediated through the intrinsic apoptotic pathway. Myofibroblast survival is prolonged by an autophagic response, as the dataset indicate that apoptosis is hastened when autophagy is inhibited. We suggest that the apoptotic death response of myofibroblasts is working in parallel with the previously observed anti-fibrotic properties of Ski within this cell type. As myofibroblasts are the sole mediators of matrix expansion in heart failure, we suggest that Ski, or a putative Ski-mimetic, may induce graded apoptosis in myofibroblasts within the failing heart and may be a novel therapeutic approach towards controlling cardiac fibrosis. Future studies are needed to examine the potential effects of Ski overexpression on other cell types in the heart.
Keywords: Myofibroblast; Ski; Apoptosis; Autophagy; Cardiac fibrosis; TGFβ1;
The multifaceted roles of the invariant chain CD74 — More than just a chaperone by Bernd Schröder (1269-1281).
The invariant chain (CD74) is well known for its essential role in antigen presentation by mediating assembly and subcellular trafficking of the MHCII complex. Beyond this, CD74 has also been implicated in a number of processes independent of MHCII. These include the regulation of endosomal trafficking, cell migration and cellular signalling as surface receptor of the pro-inflammatory cytokine macrophage migration inhibitory factor (MIF). In several forms of cancer, CD74 is up-regulated and associated with enhanced proliferation and metastatic potential. In this review, an overview of the diverse biological functions of the CD74 protein is provided with a particular focus on how these may be regulated. In particular, proteolysis of CD74 will be discussed as a central mechanism to control the actions of this important protein at different levels.
Keywords: Invariant chain; Antigen presentation; Intramembrane proteolysis; Endosomal trafficking; Macrophage migration inhibitory factor; Cell migration;
GIT1/βPIX signaling proteins and PAK1 kinase regulate microtubule nucleation by Markéta Černohorská; Vadym Sulimenko; Zuzana Hájková; Tetyana Sulimenko; Vladimíra Sládková; Stanislav Vinopal; Eduarda Dráberová; Pavel Dráber (1282-1297).
Microtubule nucleation from γ-tubulin complexes, located at the centrosome, is an essential step in the formation of the microtubule cytoskeleton. However, the signaling mechanisms that regulate microtubule nucleation in interphase cells are largely unknown. In this study, we report that γ-tubulin is in complexes containing G protein-coupled receptor kinase-interacting protein 1 (GIT1), p21-activated kinase interacting exchange factor (βPIX), and p21 protein (Cdc42/Rac)-activated kinase 1 (PAK1) in various cell lines. Immunofluorescence microscopy revealed association of GIT1, βPIX and activated PAK1 with centrosomes. Microtubule regrowth experiments showed that depletion of βPIX stimulated microtubule nucleation, while depletion of GIT1 or PAK1 resulted in decreased nucleation in the interphase cells. These data were confirmed for GIT1 and βPIX by phenotypic rescue experiments, and counting of new microtubules emanating from centrosomes during the microtubule regrowth. The importance of PAK1 for microtubule nucleation was corroborated by the inhibition of its kinase activity with IPA-3 inhibitor. GIT1 with PAK1 thus represent positive regulators, and βPIX is a negative regulator of microtubule nucleation from the interphase centrosomes. The regulatory roles of GIT1, βPIX and PAK1 in microtubule nucleation correlated with recruitment of γ-tubulin to the centrosome. Furthermore, in vitro kinase assays showed that GIT1 and βPIX, but not γ-tubulin, serve as substrates for PAK1. Finally, direct interaction of γ-tubulin with the C-terminal domain of βPIX and the N-terminal domain of GIT1, which targets this protein to the centrosome, was determined by pull-down experiments. We propose that GIT1/βPIX signaling proteins with PAK1 kinase represent a novel regulatory mechanism of microtubule nucleation in interphase cells.
Keywords: Centrosome; Microtubule nucleation; γ-tubulin; GIT1/βPIX signaling proteins; PAK1 kinase;
Oxidative folding in the mitochondrial intermembrane space: A regulated process important for cell physiology and disease by Afroditi Chatzi; Phanee Manganas; Kostas Tokatlidis (1298-1306).
Mitochondria are fundamental organelles with a complex internal architecture that fulfill important diverse functions including iron–sulfur cluster assembly and cell respiration. Intense work for more than 30 years has identified the key protein import components and the pathways involved in protein targeting and assembly. More recently, oxidative folding has been discovered as one important mechanism for mitochondrial proteostasis whilst several human disorders have been linked to this pathway. We describe the molecular components of this pathway in view of their putative redox regulation and we summarize available evidence on the connections of these pathways to human disorders.Display Omitted
Keywords: Oxidative protein folding; Mitochondrial protein import; Mitochondrial intermembrane space; Mia40; Erv1; Thiol-disulfide exchange;
Genome-wide screen identifies novel machineries required for both ciliogenesis and cell cycle arrest upon serum starvation by Ji Hyun Kim; Soo Mi Ki; Je-Gun Joung; Eric Scott; Susanne Heynen-Genel; Pedro Aza-Blanc; Chang Hyuk Kwon; Joon Kim; Joseph G. Gleeson; Ji Eun Lee (1307-1318).
Biogenesis of the primary cilium, a cellular organelle mediating various signaling pathways, is generally coordinated with cell cycle exit/re-entry. Although the dynamic cell cycle-associated profile of the primary cilium has been largely accepted, the mechanism governing the link between ciliogenesis and cell cycle progression has been poorly understood. Using a human genome-wide RNAi screen, we identify genes encoding subunits of the spliceosome and proteasome as novel regulators of ciliogenesis. We demonstrate that 1) the mRNA processing-related hits are essential for RNA expression of molecules acting in cilia disassembly, such as AURKA and PLK1, and 2) the ubiquitin–proteasome systems (UPS)-involved hits are necessary for proteolysis of molecules acting in cilia assembly, such as IFT88 and CPAP. In particular, we show that these screen hit-associated mechanisms are crucial for both cilia assembly and cell cycle arrest in response to serum withdrawal. Finally, our data suggest that the mRNA processing mechanism may modulate the UPS-dependent decay of cilia assembly regulators to control ciliary resorption-coupled cell cycle re-entry.
Keywords: High-content screen; Ciliogenesis; Cell cycle; mRNA processing; Ubiquitin–proteasome system;
Sng1 associates with Nce102 to regulate the yeast Pkh–Ypk signalling module in response to sphingolipid status by Sara García-Marqués; Francisca Randez-Gil; Sebastien Dupont; Elena Garre; Jose A. Prieto (1319-1333).
All cells are delimited by biological membranes, which are consequently a primary target of stress-induced damage. Cold alters membrane functionality by decreasing lipid fluidity and the activity of membrane proteins. In Saccharomyces cerevisiae, evidence links sphingolipid homeostasis and membrane phospholipid asymmetry to the activity of the Ypk1/2 proteins, the yeast orthologous of the mammalian SGK1–3 kinases. Their regulation is mediated by different protein kinases, including the PDK1 orthologous Pkh1/2p, and requires the function of protein effectors, among them Nce102p, a component of the sphingolipid sensor machinery. Nevertheless, the mechanisms and the actors involved in Pkh/Ypk regulation remain poorly defined. Here, we demonstrate that Sng1, a transmembrane protein, is an effector of the Pkh/Ypk module and identify the phospholipid asymmetry as key for yeast cold adaptation. Overexpression of SNG1 impairs phospholipid flipping, reduces reactive oxygen species (ROS) and improves, in a Pkh-dependent manner, yeast growth in myriocin-treated cells, suggesting that excess Sng1p stimulates the Pkh/Ypk signalling. Furthermore, we link these effects to the association of Sng1p with Nce102p. Indeed, we found that Sng1p interacts with Nce102p both physically and genetically. Moreover, mutant nce102∆ sng1∆ cells show features of impaired Pkh/Ypk signalling, including increased ROS accumulation, reduced life span and defects in Pkh/Ypk-controlled regulatory pathways. Finally, myriocin-induced hyperphosphorylation of Ypk1p and Orm2p, which controls sphingolipid homeostasis, does not occur in nce102∆ sng1∆ cells. Hence, both Nce102p and Sng1p participate in a regulatory circuit that controls the activity of the Pkh/Ypk module and their function is required in response to sphingolipid status.Nce102p and Sng1p participate in a regulatory circuit that controls the activity of the Pkh/Ypk signalling module in response to sphingolipid status.Display Omitted
Keywords: Yeast; Cold stress; Membrane properties; Phospholipid flipping; Signalling; Orm2; Myriocin;