Calpain activation by hepatitis C virus proteins inhibits the extrinsic apoptotic signaling pathway.
ABSTRACT An unresolved question regarding the physiopathology of hepatitis C virus (HCV) infection is the remarkable efficiency with which host defenses are neutralized to establish chronic infection. Modulation of an apoptotic response is one strategy used by viruses to escape immune surveillance. We previously showed that HCV proteins down-regulate expression of BH3-only Bcl2 interacting domain (Bid) in hepatocytes of HCV transgenic mice. As a consequence, cells acquire resistance to Fas-mediated apoptosis, which in turn leads to increased persistence of experimental viral infections in vivo. This mechanism might participate in the establishment of chronic infections and the resulting pathologies, including hepatocellular carcinoma. We now report that Bid is also down-regulated in patients in the context of noncirrhotic HCV-linked tumorigenesis and in the HCV RNA replicon system. We show that the nonstructural HCV viral protein NS5A is sufficient to activate a calpain cysteine protease, leading to degradation of Bid. Moreover, pharmacological inhibitors of calpains restore both the physiological levels of Bid and the sensitivity of cells toward a death receptor-mediated apoptotic signal. Finally, human HCV-related tumors and hepatocytes from HCV transgenic mice that display low Bid expression contain activated calpains. CONCLUSION: Calpains activated by HCV proteins degrade Bid and thus dampen apoptotic signaling. These results suggest that inhibiting calpains could lead to an improved efficiency of immune-mediated elimination of HCV-infected cells.
Article: Protein-based identification of quantitative trait loci associated with malignant transformation in two HER2+ cellular models of breast cancer.[show abstract] [hide abstract]
ABSTRACT: A contemporary view of the cancer genome reveals extensive rearrangement compared to normal cells. Yet how these genetic alterations translate into specific proteomic changes that underpin acquiring the hallmarks of cancer remains unresolved. The objectives of this study were to quantify alterations in protein expression in two HER2+ cellular models of breast cancer and to infer differentially regulated signaling pathways in these models associated with the hallmarks of cancer. A proteomic workflow was used to identify proteins in two HER2 positive tumorigenic cell lines (BT474 and SKBR3) that were differentially expressed relative to a normal human mammary epithelial cell line (184A1). A total of 64 (BT474-184A1) and 69 (SKBR3-184A1) proteins were uniquely identified that were differentially expressed by at least 1.5-fold. Pathway inference tools were used to interpret these proteins in terms of functionally enriched pathways in the tumor cell lines. We observed "protein ubiquitination" and "apoptosis signaling" pathways were both enriched in the two breast cancer models while "IGF signaling" and "cell motility" pathways were enriched in BT474 and "amino acid metabolism" were enriched in the SKBR3 cell line. While "protein ubiquitination" and "apoptosis signaling" pathways were common to both the cell lines, the observed patterns of protein expression suggest that the evasion of apoptosis in each tumorigenic cell line occurs via different mechanisms. Evidently, apoptosis is regulated in BT474 via down regulation of Bid and in SKBR3 via up regulation of Calpain-11 as compared to 184A1.Proteome Science 02/2012; 10(1):11. · 2.33 Impact Factor