BBA - Molecular Cell Research (v.1813, #3)
Editorial Board (i).
Gene regulation mediating fiber-type transformation in skeletal muscle cells is partly glucose- and ChREBP-dependent by Nina Hanke; Renate J. Scheibe; Georgi Manukjan; David Ewers; Patrick K. Umeda; Kin-Chow Chang; Hans-Peter Kubis; Gerolf Gros; Joachim D. Meissner (377-389).
Adaptations in the oxidative capacity of skeletal muscle cells can occur under several physiological or pathological conditions. We investigated the effect of increasing extracellular glucose concentration on the expression of markers of energy metabolism in primary skeletal muscle cells and the C2C12 muscle cell line. Growth of myotubes in 25 mM glucose (high glucose, HG) compared with 5.55 mM led to increases in the expression and activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a marker of glycolytic energy metabolism, while oxidative markers peroxisome proliferator-activated receptor γ coactivator 1α and citrate synthase decreased. HG induced metabolic adaptations as are seen during a slow-to-fast fiber transformation. Furthermore, HG increased fast myosin heavy chain (MHC) IId/x but did not change slow MHCI/β expression. Protein phosphatase 2A (PP2A) was shown to mediate the effects of HG on GAPDH and MHCIId/x. Carbohydrate response element-binding protein (ChREBP), a glucose-dependent transcription factor downstream of PP2A, partially mediated the effects of glucose on metabolic markers. The glucose-induced increase in PP2A activity was associated with an increase in p38 mitogen-activated protein kinase activity, which presumably mediates the increase in MHCIId/x promoter activity. Liver X receptor, another possible mediator of glucose effects, induced only an incomplete metabolic shift, mainly increasing the expression of the glycolytic marker. Taken together, HG induces a partial slow-to-fast transformation comprising metabolic enzymes together with an increased expression of MHCIId/x. This work demonstrates a functional role for ChREBP in determining the metabolic type of muscle fibers and highlights the importance of glucose as a signaling molecule in muscle.► Growth of myotubes in high (25 mM) glucose induces metabolic adaptations. ► Carbohydrate response element-binding protein partially mediates glucose effects. ► High glucose also increases fast myosin heavy chain (MHC) IId/x expression. ► Conclusion: high glucose induces a partial slow-to-fast transformation in myotubes.
Keywords: Glucose; Carbohydrate response element-binding protein (ChREBP); Glucose; “Slow-to-fast” metabolic transformation; Liver X receptor (LXR);
Somatostatin receptor-3 mediated intracellular signaling and apoptosis is regulated by its cytoplasmic terminal by Sajad A. War; Rishi K. Somvanshi; Ujendra Kumar (390-402).
In the present study, we describe the role of cytoplasmic terminal (C-tail) domain in regulating coupling to adenylyl cyclase, signaling, and apoptosis in human embryonic kidney (HEK-293) cells transfected with wild type (wt)-hSSTR3 and C-tail deleted mutants. Cells transfected with wt-hSSTR3 and C-tail mutants show comparable membrane expression; however, display decreased expression in presence of agonist. wt-hSSTR3 exists as preformed homodimer at cell surface in basal conditions and decreases in response to agonist. Cells expressing C-tail mutants also show evidence of homodimerization with the same intensity as wt-hSSTR3. The agonist-dependent inhibition of cyclic adenosine monophosphate (cAMP) was lost in cells expressing C-tail mutants. Agonist treatment in cells expressing wt-hSSTR3 resulted in inhibition of cell proliferation, increased expression of PARP-1, and TUNEL positivity in proliferating cell nuclear antigen (PCNA)-positive cells. The agonist mediated increase in membrane expression of protein tyrosine phosphatase (PTP) seen with wt-hSSTR3 was diminished in C-tail mutants, which was accompanied with the loss of receptor's ability to induce apoptosis. Taken together, our data provide new insights into C-tail-dependent regulation of cell signaling and apoptosis by hSSTR3.► wt-hSSTR3 exists as homodimer at cell surface and decreases in response to agonist. ► cAMP inhibition by agonist was lost in C-tail mutants when compared to wt-hSSTR3. ► Cells expressing wt-hSSTR3 were positive to TUNEL and PCNA upon agonist treatment. ► Agonist-induced apoptosis was lost in cells expressing C-tail mutants.
Keywords: Apoptosis; Cytoplasmic tail; G-protein-coupled receptor; Human somatostatin receptor-3; Photobleaching–fluorescence resonance energy transfer; Somatostatin;
The kinesin superfamily protein KIF17 is regulated by the same transcription factor (NRF-1) as its cargo NR2B in neurons by Shilpa S. Dhar; Margaret T.T. Wong-Riley (403-411).
The kinesin superfamily of motor proteins is known to be ATP-dependent transporters of various types of cargoes. In neurons, KIF17 is found to transport vesicles containing the N-methyl-d-aspartate receptor NR2B subunit from the cell body specifically to the dendrites. These subunits are intimately associated with glutamatergic neurotransmission as well as with learning and memory. Glutamatergic synapses are highly energy-dependent, and recently we found that the same transcription factor, nuclear respiratory factor 1 (NRF-1), co-regulates energy metabolism (via its regulation of cytochrome c oxidase and other mitochondrial enzymes) and neurochemicals of glutamatergic transmission (NR1, NR2B, GluR2, and nNOS). The present study tested our hypothesis that NRF-1 also transcriptionally regulates KIF17. By means of in silico analysis, electrophoretic mobility shift and supershift assays, in vivo chromatin immunoprecipitation assays, promoter mutations, and real-time quantitative PCR, we found that NRF-1 (but not NRF-2) functionally regulates Kif17, but not Kif1a, gene. NRF-1 binding sites on Kif17 gene are highly conserved among mice, rats, and humans. Silencing of NRF-1 with small interference RNA blocked the up-regulation of Kif17 mRNA and proteins (and of Grin1 and Grin2b) induced by KCl-mediated depolarization, whereas over-expressing NRF-1 rescued these transcripts and proteins from being suppressed by TTX. Thus, NRF-1 co-regulates oxidative enzymes that generate energy and neurochemicals that consume energy related to glutamatergic neurotransmission, such as KIF17, NR1, and NR2B, thereby ensuring that energy production matches energy utilization at the molecular and cellular levels.► Energy metabolism and neuronal activity are coupled at the transcriptional level. ► Nuclear respiratory factor 1 (NRF-1) is the common transcriptional regulator. ► NRF-1 co-regulates cytochrome c oxidase and NMDA receptor subunits 1 and 2B. ► Now we found that NRF-1 co-regulates NR2B and its motor, KIF17. ► Multiple approaches are used to demonstrate such a co-regulation by NRF-1.
Keywords: Excitatory neurotransmission; Gene regulation; KCl depolarization; NRF-1 over-expression; NMDA receptor; TTX;
TRP expression pattern and the functional importance of TRPC3 in primary human T-cells by Anna S. Wenning; Katherina Neblung; Bettina Strauß; Melodie-Jo Wolfs; Anne Sappok; Markus Hoth; Eva C. Schwarz (412-423).
TRP proteins form ion channels which are activated following receptor stimulation. In T-cell lines, expression data of TRP proteins have been published. However, almost no data about TRP expression is available in primary human T-cells. Using RT-PCR and quantitative RT-PCR, we compare the expression of TRP mRNA in 1) human peripheral blood lymphocytes, which are a mix of mostly mono-nuclear blood lymphocytes but contain other leucocytes, 2) a pure human CD4+ T-helper cell population in the resting (= naïve) and activated (= effector) state, and 3) two commonly used CD4+ Jurkat T-cell lines, E6-1 and parental. To mimic physiological cell stimulation, we analyzed TRP expression in primary human cells in a quantitative way over several days following formation of an immunological synapse through stimulation with antibody-coated beads. The TRP expression profile of primary human T-cells was significantly different from Jurkat T-cells. Among the TRP mRNAs of the TRPC, TRPM, and TRPV family, we found consistent expression of TRPC1, TRPC3, TRPV1, TRPM2, and TRPM7 in primary human CD4+ T-cells of all analyzed blood donors. Among these, TRPC3 and TRPM2 were strongly up-regulated following stimulation, but with different kinetics. We found that TRPC3 modulates Ca2+-dependent proliferation of primary CD4+ T-cells indicating that TRPC3 may be involved in Ca2+ homeostasis in T-cells besides the well-established STIM and ORAI proteins which are responsible for store-operated Ca2+ entry.► In primary human CD4+ T-cells, TRPC1, C3, V1, M2, and M7 are consistently expressed. ► TRPC3 and TRPM2 are up-regulated after T-cell stimulation but with different kinetics. ► STIM1 down-regulation reduces resting intracellular [Ca2+]. ► TRPC3 down-regulation reduces calcium-dependent T-cell proliferation.
Keywords: TRP channel; Primary human T-cell; Calcium; Jurkat T-cell; Quantitative RT-PCR; siRNA;
Identify submitochondria and subchloroplast locations with pseudo amino acid composition: Approach from the strategy of discrete wavelet transform feature extraction by Shao-Ping Shi; Jian-Ding Qiu; Xing-Yu Sun; Jian-Hua Huang; Shu-Yun Huang; Sheng-Bao Suo; Ru-Ping Liang; Li Zhang (424-430).
► Discrete wavelet transform (DWT) can effectively grasp the core features of the subcellular locations. ► A new method, in which SVM combines with DWT, is developed to predict the subcellular locations. ► The proposed approach can remarkably improve the predictive accuracies of the submitochondria and subchloroplast locations.
Keywords: Submitochondria locations; Subchloroplast locations; Discrete wavelet transform; Support vector machine; Pseudo amino acid composition;
Lipid rafts are essential for the regulation of SOCE by plasma membrane resident STIM1 in human platelets by Natalia Dionisio; Carmen Galán; Isaac Jardín; Ginés M. Salido; Juan. A. Rosado (431-437).
STIM1 is a transmembrane protein essential for the activation of store-operated Ca2+ entry (SOCE), a major Ca2+ influx mechanism. STIM1 is either located in the endoplasmic reticulum, communicating the Ca2+ concentration in the stores to plasma membrane channels or in the plasma membrane, where it might sense the extracellular Ca2+ concentration. Plasma membrane-located STIM1 has been reported to mediate the SOCE sensitivity to extracellular Ca2+ through its interaction with Orai1. Here we show that plasma membrane lipid raft domains are essential for the regulation of SOCE by extracellular Ca2+. Treatment of platelets with the SERCA inhibitor thapsigargin (TG) induced Mn2+ entry, which was inhibited by increasing concentrations of extracellular Ca2+. Platelet treatment with methyl-β-cyclodextrin, which removes cholesterol and disrupts the lipid raft domains, impaired the inactivation of Ca2+ entry induced by extracellular Ca2+. Methyl-β-cyclodextrin also abolished translocation of STIM1 to the plasma membrane stimulated by treatment with TG and prevented TG-evoked co-immunoprecipitation between plasma membrane-located STIM1 and the Ca2+ permeable channel Orai1. These findings suggest that lipid raft domains are essential for the inactivation of SOCE by extracellular Ca2+ mediated by the interaction between plasma membrane-located STIM1 and Orai1.► STIM1 located in the plasma membrane is involved in the regulation of SOCE. ► Lipid rafts are involved in the regulation of SOCE by plasma membrane-STIM1. ► Lipid rafts are necessary for the translocation of STIM1 to the plasma membrane. ► Lipid rafts support the association between plasma membrane-STIM1 and Orai1.
Keywords: STIM1; Orai1; Lipid raft; Platelet; Methyl-β-cyclodextrin; Calcium;
The role of DDX3 in regulating Snail by Mianen Sun; Ling Song; Tong Zhou; G. Yancey Gillespie; Richard S. Jope (438-447).
DDX3, a DEAD box protein family member, appears to promote the progression of some cancers, which may partly result from its impedance of death receptor-mediated apoptosis. We found that another mechanism by which DDX3 may aid cancer progression is by promoting increased levels of the transcription factor Snail. Snail represses expression of cellular adhesion proteins, leading to increased cell migration and metastasis of many types of cancer. Knockdown of DDX3 levels by shRNA reduced basal levels of Snail in HeLa and MCF-7 cells, and this was associated with reduced cell proliferation and migration. Snail protein and mRNA levels were increased by treatment with the HDAC inhibitors sodium butyrate or trichostatin A, and these increases were attenuated in cells with DDX3 knocked down. Treatment of cells with camptothecin was discovered to increase Snail protein levels, and this increase was diminished in cells with DDX3 knocked down. Analysis of 31 patient glioblastoma multiforme (GBM) samples revealed a significant correlation between the levels of DDX3 and Snail. Thus, DDX3 is required for basal Snail expression and increases in Snail induced by HDAC inhibitors or camptothecin, indicating that this action of DDX3 may contribute to its promotion of the progression of some cancers.► DDX3 knockdown alters Snail levels and cell migration. ► HDAC inhibitors upregulate Snail expression levels. ► DDX3 is required for HDAC inhibitor-induced Snail expression. ► Topoisomerase inhibitors increase Snail expression. ► DDX3 regulating camptothecin-induced Snail is a post-translational effect.
Keywords: DDX3; Snail; HDAC; Camptothecin; Metastasis;
Functional modulation of AMP-activated protein kinase by cereblon by Kwang Min Lee; Sooyeon Jo; Hyunyoung Kim; Jongwon Lee; Chul-Seung Park (448-455).
Mutations in cereblon (CRBN), a substrate binding component of the E3 ubiquitin ligase complex, cause a form of mental retardation in humans. However, the cellular proteins that interact with CRBN remain largely unknown. Here, we report that CRBN directly interacts with the α1 subunit of AMP-activated protein kinase (AMPK α1) and inhibits the activation of AMPK activation. The ectopic expression of CRBN reduces phosphorylation of AMPK α1 and, thus, inhibits the enzyme in a nutrient-independent manner. Moreover, AMPK α1 can be potently activated by suppressing endogenous CRBN using CRBN-specific small hairpin RNAs. Thus, CRBN may act as a negative modulator of the AMPK signaling pathway in vivo. ►Cereblon (CRBN) directly interacts with the AMP-activated protein kinase (AMPK) α1. ►Expression of CRBN reduces the phosphorylation of AMPK α1. ►AMPK α1 can be potently activated by suppressing endogenous CRBN.
Keywords: Cereblon; AMP-activated protein kinase α1; Autosomal recessive nonsyndromic mental retardation; Binding protein;
Cytoskeletal remodeling by C3G to induce neurite-like extensions and inhibit motility in highly invasive breast carcinoma cells by Kunal Dayma; Vegesna Radha (456-465).
Cytoskeletal remodeling is responsible for cell plasticity and facilitates differentiation, motility and adherence related functions. C3G (RAPGEF1), an exchange factor for Ras family of small GTPases, regulates cytoskeletal reorganization to induce filopodia in epithelial cells and neurite growth in neuroblastoma cells. Here we show that C3G overexpression induces neurite-like extensions (NLE) in MDA-MB-231 and BT549 breast carcinoma cells and not in a variety of other cancer cell lines examined. These processes were actin-rich with nodes, branches and microspikes. C3G associates with the cytoskeleton and its expression enabled stabilization of microtubules. NLE formation was dependent on Rap, Rac and Cdc42. C3G expression was associated with a decrease in cellular β-catenin levels specifically in MDA-MB-231 and BT549 cells. β-Catenin stabilization induced by GSK-3β inhibition, or coexpression of β-catenin, reduced C3G induced NLE formation. Time lapse analysis showed reduced motility of C3G expressing cells compared to GFP expressing cells. Our results suggest that C3G overexpression can induce phenotypic characteristics of neuronal cells in highly invasive breast cancer cells and inhibit their motility.► The ubiquitously expressed guanine nucleotide exchange factor C3G induced morphological differentiation of neurons specifically in highly invasive breast cancer cells. ► Microtubule stabilization and neurite-like extension formation represent previously undescribed functions of C3G. ► Morphological changes caused by C3G correlate with its ability to repress cellular β-catenin protein levels. ► C3G expression inhibits motility of aggressive breast cancer cells MDA-MB-231.
Keywords: C3G; RAPGEF1; Guanine nucleotide exchange factor; Neurite-like extensions; MDA-MB-231; Cytoskeleton;
Heterotrimeric Gαi proteins are regulated by lipopolysaccharide and are anti-inflammatory in endotoxemia and polymicrobial sepsis by Hongkuan Fan; Pengfei Li; Basilia Zingarelli; Keith Borg; Perry V. Halushka; Lutz Birnbaumer; James A. Cook (466-472).
Previous studies have implicated a role of heterotrimeric Gαi proteins in lipopolysaccharide (LPS)-induced inflammatory responses. We hypothesized that Toll-like receptor (TLR) signaling regulates Gαi proteins, which are anti-inflammatory in endotoxemia and polymicrobial sepsis. RAW 264.7 cells were stimulated with LPS and the Gαi–GTP protein complex was immunoprecipitated with a Gαi protein activation assay. In subsequent in vivo studies, the Gαi protein inhibitor pertussis toxin (PTx) or Gi protein agonist mastoparan (MP-7) were administrated prior to endotoxemia. LPS-induced pro-inflammatory cytokines and mortality were determined. To examine the role of Gαi2 in sepsis, Gαi2 (−/−) and wildtype (WT) mice were subjected to cecal ligation and puncture (CLP) and monitored every 24 h for 120 h. Other mice were sacrificed 24 h after CLP. Peritoneal fluid, blood, and tissue samples were collected. Plasma pro-inflammatory cytokine production, bacterial load in peritoneal fluid, blood and lung tissue, myeloperoxidase (MPO) activity in lung and liver and different immune cell populations in spleen were studied. We found that Gαi proteins are rapidly activated by LPS followed by rapid inactivation. These studies provide the first direct evidence that Gαi proteins are modulated by TLR signaling. In following studies, PTx augmented LPS-induced plasma TNFα, IL-6, whereas MP-7 suppressed LPS-induced TNFα and decreased LPS-induced mortality. In sepsis studies, the survival rate post-CLP was significantly decreased in the Gαi2 (−/−) mice compared to WT mice. CLP-induced plasma TNFα, IL-6, bacterial load in peritoneal fluid, blood and lung tissue and lung and liver MPO activity were significantly increased in Gαi2 (−/−) compared to WT mice. Gαi2 (−/−) mice also exhibited increased Th1 and Th2 responses compared to WT mice. Taken together, Gαi proteins are activated by LPS and negatively regulate endotoxemia and sepsis. Understanding the role of Gαi2 protein in regulation of the inflammatory response in sepsis may provide novel targets for treatment of sepsis.► Gαi proteins are activated by LPS stimulation. ► Gαi proteins negatively regulate endotoxemia. ► Gαi2 protein negatively regulates polymicrobial sepsis.
Keywords: Gαi protein; Cecal ligation and puncture; LPS; Pertussis toxin; Mastoparan;
The N-terminal region of RECQL4 lacking the helicase domain is both essential and sufficient for the viability of vertebrate cells by Takuya Abe; Akari Yoshimura; Yoshifumi Hosono; Shusuke Tada; Masayuki Seki; Takemi Enomoto (473-479).
Rothmund–Thomson syndrome (RTS) is a rare genetic disorder characterized by premature aging, developmental abnormalities, and a predisposition to cancer. RTS is caused by mutations in the RECQL4 gene, which encodes one of the five human RecQ helicases. To identify the cellular functions of RECQL4, we generated a chicken DT40 cell line in which RECQL4 expression could be turned off by doxycycline (Dox). Upon exposure to Dox, cells stopped growing and underwent apoptosis. The cells could be rescued by expression of the N-terminal region of RECQL4 (amino acids 1–496), which lacks the helicase domain and has sequence similarity to yeast Sld2, which plays an essential function in the initiation of DNA replication in Saccharomyces cerevisiae. Smaller fragments of the N-terminal region of RECQL4 did not rescue the cells from lethality. RECQL4 gene knockout cells complemented with RECQL4 (1–496) showed relatively high sensitivity to DNA damaging agents that induce double strand breaks and cross-links, suggesting that the C-terminal region including the helicase domain of RECQL4 is involved in the repair of certain types of DNA lesions.► The N-terminal region of RECQL4 is sufficient for the viability of vertebrate cells. (84) ► The helicase domain of RECQL4 is not necessary for viability. (61) ► The C-terminal region of RECQL4 is involved in the repair of DNA lesions. (73)
Keywords: RecQL4; Rothmund–Thomson syndrome; RecQ helicase; DNA repair; Sld2;
Presenilin-1 processing of ErbB4 in fetal type II cells is necessary for control of fetal lung maturation by Kristina Hoeing; Katja Zscheppang; Sana Mujahid; Sandy Murray; MaryAnn V. Volpe; Christiane E.L. Dammann; Heber C. Nielsen (480-491).
Maturation of pulmonary fetal type II cells to initiate adequate surfactant production is crucial for postnatal respiratory function. Little is known about specific mechanisms of signal transduction controlling type II cell maturation. The ErbB4 receptor and its ligand neuregulin (NRG) are critical for lung development. ErbB4 is cleaved at the cell membrane by the γ-secretase enzyme complex whose active component is either presenilin-1 (PSEN-1) or presenilin-2. ErbB4 cleavage releases the 80 kDa intracellular domain (4ICD), which associates with chaperone proteins such as YAP (Yes-associated protein) and translocates to the nucleus to regulate gene expression. We hypothesized that PSEN-1 and YAP have a development-specific expression in fetal type II cells and are important for ErbB4 signaling in surfactant production. In primary fetal mouse E16, E17, and E18 type II cells, PSEN-1 and YAP expression increased at E17 and E18 over E16. Subcellular fractionation showed a strong cytosolic and a weaker membrane location of both PSEN-1 and YAP. This was enhanced by NRG stimulation. Co-immunoprecipitations showed ErbB4 associated separately with PSEN-1 and with YAP. Their association, phosphorylation, and co-localization were induced by NRG. Confocal immunofluorescence and nuclear fractionation confirmed these associations in a time-dependent manner after NRG stimulation. Primary ErbB4-deleted E17 type II cells were transfected with a mutant ErbB4 lacking the γ-secretase binding site. When compared to transfection with wild-type ErbB4, the stimulatory effect of NRG on surfactant protein mRNA expression was lost. We conclude that PSEN-1 and YAP have crucial roles in ErbB4 signal transduction during type II cell maturation.► Presenilin-1 and Yes-associated protein (YAP) are developmentally expressed in fetal lung type II epithelial cells. ► ErbB4 activation in fetal type II cells includes cleavage by presenilin-1 and association of the intracellular fragment with YAP for nuclear transport. ► Presenilin-1 cleavage of ErbB4 is necessary for stimulation of surfactant protein synthesis by neuregulin, the ErbB4 ligand.
Keywords: ErbB receptors; Gamma secretase; Yes-associated protein; Fetal lung; Type II cells; Surfactant proteins;
Involvement of p53 in cell death following cell cycle arrest and mitotic catastrophe induced by rotenone by António Pedro Gonçalves; Valdemar Máximo; Jorge Lima; Keshav K. Singh; Paula Soares; Arnaldo Videira (492-499).
In order to investigate the cell death-inducing effects of rotenone, a plant extract commonly used as a mitochondrial complex I inhibitor, we studied cancer cell lines with different genetic backgrounds. Rotenone inhibits cell growth through the induction of cell death and cell cycle arrest, associated with the development of mitotic catastrophe. The cell death inducer staurosporine potentiates the inhibition of cell growth by rotenone in a dose-dependent synergistic manner. The tumor suppressor p53 is involved in rotenone-induced cell death, since the drug treatment results in increased expression, phosphorylation and nuclear localization of the protein. The evaluation of the effects of rotenone on a p53-deficient cell line revealed that although not required for the promotion of mitotic catastrophe, functional p53 appears to be essential for the extensive cell death that occurs afterwards. Our results suggest that mitotic slippage also occurs subsequently to the rotenone-induced mitotic arrest and cells treated with the drug for a longer period become senescent. Treatment of mtDNA-depleted cells with rotenone induces cell death and cell cycle arrest as in cells containing wild-type mtDNA, but not formation of reactive oxygen species. This suggests that the effects of rotenone are not dependent from the production of reactive oxygen species. This work highlights the multiple effects of rotenone in cancer cells related to its action as an anti-mitotic drug.► Rotenone induces cell death, cell cycle arrest and mitotic catastrophe. ► p53 is essential for the extensive rotenone-induced cell death. ► Rotenone effects are not dependent from the production of reactive oxygen species. ► Staurosporine potentiates the inhibition of cell growth by rotenone.
Keywords: Cell death; Rotenone; p53; Mitotic catastrophe; Cell cycle;
Calmodulin regulates the non-amyloidogenic metabolism of amyloid precursor protein in platelets by I. Canobbio; S. Catricalà; C. Balduini; M. Torti (500-506).
A balance between the proteolytic processing of amyloid precursor protein APP through the amyloidogenic and the non-amyloidogenic pathways controls the production and release of amyloid β-protein, whose accumulation in the brain is associated to the onset of Alzheimer Disease. APP is also expressed on circulating platelets. The regulation of APP processing in these cells is poorly understood. In this work we show that platelets store considerable amounts of APP fragments, including sAPPα, that can be released upon stimulation of platelets. Moreover, platelet stimulation also promotes the proteolysis of intact APP expressed on the cell surface. This process is supported by an ADAM metalloproteinase, and causes the release of sAPPα. Processing of intact platelet APP is promoted also by treatment with calmodulin antagonist W7. W7-induced APP proteolysis occurs through the non-amyloidogenic pathway, is mediated by a metalloproteinase, and causes the release of sAPPα. Co-immunoprecipitation and pull-down experiments revealed a physical association between calmodulin and APP. These results document a novel role of calmodulin in the regulation of non-amyloidogenic processing of APP.► Agonist platelets induce proteolysis of APP through the non-amyloidogenic pathway. ► Calmodulin antagonist promotes APP proteolysis in resting platelets. ► Calmodulin is a binding partner for APP in platelets.
Keywords: Amyloid precursor protein; Human platelets; Proteolysis; Calmodulin;