c-FLIPL regulates PKC via AP-2 to inhibit Bax-mediated apoptosis induced by HIV-1 gp120 in Jurkat cells

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Molecular and Cellular Biochemistry (Impact Factor: 2.39). 05/2009; 330(1-2):23-9. DOI: 10.1007/s11010-009-0096-3
Source: PubMed


c-FLIPL, an inhibitor of caspase 8, is known to inhibit the Fas/caspase 8 apoptotic pathway; however, its involvement of Bax/mitochondrial apoptosis is not well understood. Using human cells, Jurkat cell line, induced with HIV-1 gp120, we studied the effects of c-FLIPL on Bax/mitochondrial apoptosis. We found that the induction of apoptosis by HIV-1 envelope protein, gp120, involved the activation of both Bax-dependent and death receptor-mediated pathways, and HIV-1 infection deceased c-FLIPL expression. Interestingly, c-FLIPL expression downregulated protein kinase C (PKC) expression at the transcript level involving activated protein-2 (AP-2). c-FLIPL expression reduced AP-2 protein levels required to promote PKC protein expression and PKC-associated inactive form of Bax, and inhibited Bax activation, suggesting that c-FLIPL inhibits Bax activation via modulating PKC expression at the transcriptional level involving AP-2 during gp120 treatment. Collectively, these findings further corroborate the concept that gp120 plays an important role, via involvement of molecules such as c-FLIPL, in apoptotic cell death due to HIV-1 infection.

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    • "Caspase-8 is a critical component of DISC where caspase-8 cleavage from its trimer to become the active form of caspase-8 necessary to activate the effector caspases, such as caspase-3, in the downstream of Fas signaling [10]. 1 MOI of virus H1N1pdm- infected A549 cells displayed more caspase-8 cleavage from day 2 (Fig. 3A) which suggests that H1N1pdm infection is able to induce apoptosis in A549 cells through Fas signaling. FLIP, for example, is an inhibitor of caspase-8, and increased recruitment of FLIP into DISC results in blockage of caspase-8 activity [12] [13], which inhibits Fas-mediated apoptotic signaling and virus replication (Fig. 2B). To test the effect of caspase-8 inhibition on H1N1pdm production, A549 cells were infected with 1 MOI of virus for 2 h, and then incubated in Fig. 2. Virus infection modulated molecules of components in DISC formation and expression of them impacts viral replication. "
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    ABSTRACT: Background: It is known that cigarette smoke (CS) causes cell death. Apoptotic cell death is involved in the pathogenesis of CS-related lung diseases. Some members of the protein kinase C (PKC) family have roles in cigarette smoke extract (CSE)-induced apoptosis. This study was conducted to investigate the role of PKC epsilon in CSE-induced apoptosis in human lung fibroblast cell line, MRC-5. Methods: Lactate dehydrogenase release was measured using a cytotoxicity detection kit. The MTT assay was used to measure cell viability. Western immunoblot, Hoechst 33342 staining and flow cytometry were used to demonstrate the effect of PKC ε.. Caspase-3 and caspase-8 activities were determined using a colorimetric assay. To examine PKC ε activation, Western blotting was performed using both fractions of membrane and cytosol. Results: We showed that CSE activated PKC ε by demonstrating increased expression of PKC ε in the plasma membrane fraction. Pre-treatment of PKC ε peptide inhibitor attenuated CSE-induced apoptotic cell death, as demonstrated by the MTT assay (13.03% of control, 85.66% of CSE-treatment, and 53.73% of PKC ε peptide inhibitor-pre-treatment, respectively), Hoechst 33342 staining, and flow cytometry (85.64% of CSE-treatment, 53.73% of PKC ε peptide inhibitor-pre-treatment). Pre-treatment of PKC ε peptide inhibitor reduced caspase-3 expression and attenuated caspase-3, caspase-8 activity compared with CSE treatment alone. Conclusion: PKC ε seem to have pro-apoptotic function and exerts its function through the extrinsic apoptotic pathway in CSE-exposed MRC-5 cells. This study suggests that PKC ε inhibition may be a therapeutic strategy in CS-related lung disease such as chronic obstructive pulmonary disease. Copyright©2011. The Korean Academy of Tuberculosis and Respiratory Diseases. All rights reserved.
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