Inhibition of hepatitis C virus core protein expression in immortalized human hepatocytes induces cytochrome c-independent increase in Apaf-1 and caspase-9 activation for cell death.
Hepatitis C virus (HCV) core protein has multifunctional activities. We have previously reported that the core protein of HCV immortalizes primary human hepatocytes, which may relate to multistage hepatocarcinogenic events. These immortalized human hepatocytes (IHH) served as a model to study the mechanism of HCV core protein-mediated cell growth regulation. Inhibition of core protein expression in earlier stages after hepatocyte immortalization leads to the induction of apoptosis. Here, we have observed that introduction of antisense core (AS-Core) sequences for inhibition of core protein expression enhanced the expression of E2F1 and p53 levels in early passage IHH. Inhibition of core protein expression also altered the expression level of Bcl-2 family proteins, displaying an increase of the proapoptotic Bax and a decrease in the level of the anti-apoptotic Bcl-xL proteins. These alterations, however, did not result in the release of cytochrome c from the mitochondria. Apaf-1 is frequently deregulated under various pathologic conditions, and examination of AS-Core-expressing apoptotic cells indicated a significant increase in the level of Apaf-1, which coincided with caspase-9 activation. Knockdown of Apaf-1 or the transcriptional regulatory proteins, E2F1 or p53, by small interfering RNA (siRNA) duplexes inhibited the activation of caspase-9 and enhanced cell viability in AS-Core-expressing cells. These findings may contribute to the understanding of the pathophysiology of HCV core protein-mediated hepatocyte growth regulation and disease progression.
Meyer
Keith
K
Department of Internal Medicine, Saint Louis University, St. Louis, MO 63110, USA.
Basu
Arnab
A
Saito
Kousuke
K
Ray
Ratna B
RB
Ray
Ranjit
R
D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002472:Cell Transformation, Viral; D045304:Cytochromes c / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D015967:Gene Expression Regulation, Viral / Q000187:drug effects; D016174:Hepacivirus / Q000235:genetics / Q000502:physiology*; D022781:Hepatocytes; D006801:Humans; D011506:Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016372:RNA, Antisense / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014758:Viral Core Proteins / Q000235:genetics / Q000502:physiology*
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016372:RNA, Antisense; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; D045304:Cytochromes c; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases