Current Molecular Medicine (v.12, #3)
Involvement of IL-1R/TLR Signalling in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis by V. Ruggiero (218-236).
Multiple sclerosis is a complex disease characterised by chronic inflammation, demyelination and axonal pathology resulting in progressive neurological disabilities. Multiple sclerosis is generally considered to be an autoimmune disease, even though the primary cause of the underlying autoimmune response is unknown. Epidemiological evidence suggests that both genetic and environmental factors play a key role in susceptibility to multiple sclerosis; however, the relative contributions of these factors in triggering the onset of the disease remain unclear. Several studies indicate that receptors belonging to the Interleukin-1 and Toll-like receptor families are crucially involved in the mechanisms underlying the development of experimental autoimmune encephalomyelitis, an animal model that mimics multiple sclerosis. Moreover, recent evidence highlights the importance of downstream signalling proteins in the Interleukin-1 and Toll-like receptor signalling pathways, namely, myeloid differentiation primary response protein 88 and Interleukin-1-receptor-associated kinase. This review summarises the current knowledge concerning the involvement of Interleukin-1/Toll-like receptor signalling in the development of experimental autoimmune encephalomyelitis and multiple sclerosis. A deeper understanding of the role of these important pathways in the pathogenesis of experimental autoimmune encephalomyelitis may eventually yield clinical benefits in the treatment of central nervous system-based inflammatory disorders.
DNA Repair Mechanisms in Colorectal Carcinogenesis by C. Michailidi (237-246).
Colon cancer is among the most common cancers and the third cause of cancer deaths worldwide. If detected at an early stage, treatment might often lead to cure. The present review adduces the so far studied alterations in the expression of genes, as well as polymorphisms of genes engaged in DNA repair systems, with particular emphasis on indirect ones that are correlated with colorectal cancer. Such aberrations could be linked to an increased risk for the development of colorectal cancer and might serve as potential targets in the areas of prevention and therapy.
Emerging Roles of MicroRNA-22 in Human Disease and Normal Physiology by J. Xiong (247-258).
MicroRNAs (miRNAs) are an abundant class of small noncoding RNAs that have critical regulatory functions in various biological processes. MicroRNA-22 (miR-22) is a highly-conserved 22-nt miRNA, whose roles in human diseases and normal physiology are just beginning to emerge. Recently, miR-22 has been connected to a great number of activities that encompass tumorigenesis, epigenetic modification, embryonic development, skeletal metabolism, panic disorder, and cardiomyocyte hypertrophy. Aberrant expression of miR-22 has been identified in multiple human diseases. Here, we describe our current understanding of the roles of miR-22 and its signaling circuitry in pathology and physiology, and discuss important advances that set the scene for applying miR-22 to the prevention and treatment of a wide range of human diseases.
The PD-1/PD-L1 Pathway in Human Pathology by M. Saresella (259-267).
T-cell activation is dependent on signals delivered through the antigen-specific T-cell receptor and accessory receptors on T-cells. Integration of signals through this family of costimulatory and inhibitory receptors and their ligands regulates the balance between T-cell activation, tolerance, and immunopathology. Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, deliver inhibitory signals and exert a vital and diverse range of immunoregulatory roles in T-cell activation, tolerance, and immune-mediated tissue damage. In this review, we revisit current understanding of the immunoregulatory functions of PD-1 and its ligands and their involvement in immune-mediated diseases.
The Role and Therapeutic Potential of Ser/Thr Phosphatase PP2A in Apoptotic Signalling Networks in Human Cancer Cells by V. Janssens (268-287).
A block in apoptotic cell death is a likely requirement for cancer maintenance. Likewise, drug resistance, one of the key clinical problems in oncology, can often be explained by apoptotic resistance following drug administration. Several signalling pathways can commit cells to death, including intrinsic mitochondrial pathways controlled by the Bcl-2-like proteins, extrinsic Death Receptor-triggered pathways, and Dependence Receptor-initiated pathways. In addition, depending on the cell type, external stimulus and context, various other pro- or anti-survival signalling pathways may become repressed or activated. Proper coordination and conversion into a common cellular response is ensured by various ways of inter-pathway crosstalk. As for most signalling cascades, post-translational control of the signalling proteins involved is mainly achieved by reversible phosphorylation and thus by the coordinated actions of protein kinases and phosphatases. Despite increasing interest in phosphatases as potential tumour suppressors, their role in controlling apoptotic signalling remains poorly understood. Here we review current knowledge about the regulatory functions of Protein Phosphatase type 2A (PP2A) phosphatases in these apoptotic signalling networks. PP2A represents an abundant class of structurally complex Ser/Thr phosphatases which are of particular interest in this context because of their recently established role as genuine tumour suppressors. In line with these tumour suppressive characteristics, PP2A predominantly displays pro-apoptotic functions, although some PP2A complexes also clearly counteract apoptotic cell death. Finally, we speculate how this knowledge might be exploited for therapeutic purposes, in light of pre-clinical pharmacological approaches, currently demonstrated to target PP2A in cancer cells.
The Impact of the Activated Stroma on Pancreatic Ductal Adenocarcinoma Biology and Therapy Resistance by Mert Erkan (288-303).
Around 95% of patients diagnosed with pancreatic cancer will die of their disease within 5 years, three quarters within a year. The major hurdle in improving prognosis is the lack of a therapeutic time window. Early cancerous lesions are far beneath our threshold of detection. Therefore, at the time of diagnosis even early (T1) tumors can be metastatic and resistant to conventional treatments. Several therapies targeting epithelial tumor cells—all showing impressive results in vitro and in animal experiments—have failed to show relevant effects in clinical trials. This discrepancy between experimental data and clinical reality results mostly from the inefficiency of our current experimental setups in recreating the tumor microenvironment. Forming more than 80% of the tumor mass, the fibrotic stroma of pancreatic ductal adenocarcinoma is not a passive scaffold for the malignant cells but an active player in carcinogenesis. This component is mostly missing in the xeno-/allograft- mouse models. Although tumors are bigger if stellate cells are co-implanted, due to the disproportionate cancer/stromal cell ratio and –possibly– too rapid tumor growth, the stromal reaction is much smaller than in human pancreatic cancer. One the other hand, desmoplasia is present only in some of the genetically engineered mouse models. Clinically, stromal activity of the pancreatic ductal adenocarcinoma has as great an impact on patient prognosis as the lymph node status of the tumor. The exact molecular mechanisms behind this observation remain obscure. However, one possible fundamental biologic explanation could be that selective pressure applied by the stroma leads to the evolution of cancer cells. Consequently, somatic evolution of invasive cancer could be viewed as a sequence of phenotypical adaptations to this barrier, highlighting the importance of the fibrotic tumor microenvironment in the behavior of pancreatic cancer. In this review, the interaction of the epithelial tumor cells with the stroma in humans and in various animal models is scrutinized, and novel therapeutic options for uncoupling cancer-stroma interactions are discussed.
Cellular Prion and its Catabolites in the Brain: Production and Function by M.-V. Guillot-Sestier (304-315).
During the last thirty years, part of the scientific community focused on the mechanisms by which a naturally occurring protein called cellular prion (PrPc) converts into a protease-resistant isoform (PrPsc) responsible for fatal Transmissible Spongiform Encephalopathies (TSE). Concomitantly, the physiology of PrPc has also been studied. PrPc undergoes proteolytic attacks leading to both membrane-attached and secreted fragments, the nature of which differs in normal and TSE-affected human brains. Does proteolysis of PrPc correspond to an inactivating mechanism impairing the biological function of the protein, or alternatively, does it represent a maturation process allowing the produced fragments to trigger their own physiological function? Here we review the mechanisms involved in the production of PrPc catabolites and we focus on the function of PrPc and its derived fragments in the cell death/ survival regulation in the nervous system.
AAV-Mediated Gene Therapy in Mouse Models of Recessive Retinal Degeneration by J.-J. Pang (316-330).
In recent years, more and more mutant genes that cause retinal diseases have been detected. At the same time, many naturally occurring mouse models of retinal degeneration have also been found, which show similar changes to human retinal diseases. These, together with improved viral vector quality allow more and more traditionally incurable inherited retinal disorders to become potential candidates for gene therapy. Currently, the most common vehicle to deliver the therapeutic gene into target retinal cells is the adenoassociated viral vector (AAV). Following delivery to the immuno-privileged subretinal space, AAV-vectors can efficiently target both retinal pigment epithelium and photoreceptor cells, the origin of most retinal degenerations. This review focuses on the AAV-based gene therapy in mouse models of recessive retinal degenerations, especially those in which delivery of the correct copy of the wild-type gene has led to significant beneficial effects on visual function, as determined by morphological, biochemical, electroretinographic and behavioral analysis. The past studies in animal models and ongoing successful LCA2 clinical trials, predict a bright future for AAV gene replacement treatment for inherited recessive retinal diseases.
Genomic Sequencing of Key Genes in Mouse Pancreatic Cancer Cells by Y. Wang (331-341).
Pancreatic cancer is a multiple genetic disorder with many mutations identified during the progression. Two mouse pancreatic cancer cell lines were established which showed different phenotype in vivo: a non-metastatic cell line, Panc02, and a highly metastatic cell line, Panc02-H7, a derivative of Panc02. In order to investigate whether the genetic mutations of key genes in pancreatic cancer such as KRAS, TP53 (p53), CDKN2A (p16), SMAD4, ZIP4, and PDX-1 contribute to the phenotypic difference of these two mouse pancreatic cancer cells, we sequenced the exonic regions of these key genes in both cell lines and in the normal syngeneic mouse pancreas and compared them with the reference mouse genome sequence. The exons of KRAS, SMAD4, CDKN2A (p16), TP53 (p53), ZIP4, and PDX-1 genes were amplified and the genotype of these genes was determined by Sanger sequencing. The sequences were analyzed with Sequencher software. A mutation in SMAD4 was identified in both cell lines. This homozygote G to T mutation in the first position of codon 174 (GAA) generated a stop codon resulting in the translation of a truncated protein. Further functional analysis indicates that different TGF-β/SMAD signaling pathways were involved in those two mouse cell lines, which may explain the phonotypic difference between the two cells. A single nucleotide polymorphism (SNP) in KRAS gene (TAT to TAC at codon 32) was also identified in the normal pancreas DNA of the syngenic mouse and in both derived tumoral Panc02 and Panc02-H7 cells. No mutation or SNP was found in CDKN2A (p16), TP53 (p53), ZIP4, and PDX-1 genes in these two cell lines. The absence of mutations in genes such as KRAS, TP53, and CDKN2A, which are considered as key genes in the development of human pancreatic cancer suggests that SMAD4 might play a central and decisive role in mouse pancreatic cancer. These results also suggest that other mechanisms are involved in the substantial phenotypic difference between these two mouse pancreatic cancer cell lines. Further studies are warranted to elucidate the molecular pathways that lead to the aggressive metastatic potential of Panc02-H7.
Combination of Valproic Acid and ATRA Restores RARβ2 Expression and Induces Differentiation in Cervical Cancer through the PI3K/Akt Pathway by D. Feng (342-354).
Epigenetic silencing of the tumor suppressor gene, RARβ2, through histone deacetylation has been established as an important process of cervical carcinogenesis. This pivotal role has led to the suggestion that a combination of retinoids selective for RARβ2 with histone deacetylase (HDAC) inhibitors may have therapeutic potential. Valproic acid (VPA), a HDAC inhibitor, has a critical role in the regulation of gene expression through histone acetylation and causes transformed cells to undergo growth arrest, differentiation, and apoptosis. Therefore, we hypothesized that the combination of VPA and ATRA could restore RARβ2 expression, thus resulting in enhanced anti-neoplastic activity in cervical cancer. Here, we show that VPA combined with ATRA led to hyperacetylation of histone H3 and a significant alteration of gene expression in cervical cancer cells, including RARβ2 gene expression, which was upregulated 50- to 90-fold. The combination therapy effectively inhibited the growth of cervical cancer cells more than the single agent treatment both in vitro and in vivo. The additive effects were associated with a significant upregulation of p21CIP1 and p53 as well as a pronounced decrease in p-Stat3. Furthermore, the combined treatment led to cell cycle arrest predominantly at the G1 phase, and it preferentially induced cell differentiation rather than apoptosis in cervical cancer cells. The differentiation program was determined by the presence of E-cadherinmediated adhesion and activation of the PI3K/Akt pathway. Taken together, these results provide new insight into the mechanisms of enhanced antitumor activity of the HDAC inhibitor and ATRA regimen, thus offering a new therapeutic strategy for cervical cancer patients.