Hepatitis C viral proteins interact with Smad3 and differentially regulate TGF-beta/Smad3-mediated transcriptional activation.
Transforming growth factor-beta (TGF-beta) is a pleiotropic cytokine implicated as a pathogenic mediator in various liver diseases. Enhanced TGF-beta production and lack of TGF-beta responses are often observed during hepatitis C virus (HCV) infection. In this study, we demonstrate that TGF-beta-mediated transactivation is decreased in cells exogenously expressing the intact HCV polyprotein. Among 10 viral products of HCV, only core and nonstructural protein 3 (NS3) physically interact with the MH1 (Mad homology 1) region of the Smad3 and block TGF-beta/Smad3-mediated transcriptional activation through interference with the DNA-binding ability of Smad3, not the nuclear translocation. However, the interactive domain of NS3 extends to the MH2 (Mad homology 2) region of Smad3 and a distinction is found between effects mediated, respectively, by these two viral proteins. HCV core, in the presence or absence of TGF-beta, has a stronger suppressive effect on the DNA-binding and transactivation ability of Smad3 than NS3. Although HCV core, NS3, and the HCV subgenomic replicon all attenuate TGF-beta/Smad3-mediated apoptosis, only HCV core represses TGF-beta-induced G1 phase arrest through downregulation of the TGF-beta-induced p21 promoter activation. Along with this, HCV core, rather than NS3, exhibits a significant inhibitory effect on the binding of Smad3/Sp1 complex to the proximal p21 promoter in response to TGF-beta. In conclusion, HCV viral proteins interact with the TGF-beta signaling mediator Smad3 and differentially impair TGF-beta/Smad3-mediated transactivation and growth inhibition. This functional counteraction of TGF-beta responses provides insights into possible mechanisms, whereby the HCV oncogenic proteins antagonize the host defenses during hepatocarcinogenesis.
Cheng
Pei-Lin
PL
Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan 112, Republic of China.
Chang
Meng-Hsiung
MH
Chao
Chi-Hong
CH
Lee
Yan-Hwa Wu
YH
D017209:Apoptosis; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D016174:Hepacivirus; D006801:Humans; D008113:Liver Neoplasms; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D014758:Viral Core Proteins / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D014758:Viral Core Proteins; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C497790:SMAD3 protein, human