An intrahepatic mRNA expression profile of interferon-inducible antiviral genes in chronic hepatitis C: Relative importance of a dsRNA-dependent protein kinase system

Abstract

Backgrounds: In viral hepatitis including chronic hepatitis C (CH-C), interferon (IFN) mediates antiviral response, which involves the action of multiple IFN-inducible proteins, such as a dsRNA-dependent protein kinase (PKR) system, a 2'-5' oligoadenylate synthetase (2,5-AS) and latent cellular endoribonuclease (RNase L) system, and MxA protein. While involvement of PKR in the anti-hepatitisC virus (HCV) effect of IFN was suggested, relativecontributionof other JFN-inducible protein is unknown. The aim was to clarify the intrahepatic mRNA expression profile of these IFN-inducible genes in CH-C. Methods: Sixty patients without IFN treatment who had undergone liver biopsy were included: CH-C (n= 28), chronic hepatitis B (CH-B)(n=6), autoimmune hepatitis (AIH)(n=9), primary biliary cirrhosis (PBC)(n=5), alcoholic liver disease (ALD)(n=7), and normal liver (NL)(n=5). Total RNA was extracted, and doublestranded eDNA was synthesized. The amount of mRNA for PKR, 2,5-AS, RNase L, RNase L inhibitor (RNase L-I), and MxA was quantified by competitive PCR. The values were corrected by the GAPDH mRNA expression. The expressionof each gene was compared~mo~g .diseases by Mann-Whitney's U test. Results: In our system, detection limits of PKR, 2,5-AS, RNase L, RNase L-I, and MxA mRNA were 0.2, 0.005, 0.1, 0.03, and 0.5 kcopy/10ng eDNA. PKRlGAPDH ratios (xlO-) were as follows (median [range]): CH-C; 2.9 [0.026-110], CH-B; 0.79 [0.02-8.3], AIH; 0.56 [0.14-9.1], PBC; 0.55 [0.25-0.74], ALD; 0.23 [0.042-8.3], and NL; 0.74 [0.12-0.89]. PKR mRNA was significantly overexpressed in CH-C (p=0.OO68). In addition, the amount of the PKR mRNA positively correlated with serum ALT levels in CH-C (r=0.51, p=0.0054). RNase L-U GAPDH ratios (xI0-) were as follows: CH-C; 0.011 [0-143], CH-B; 41 [0-723], AIH; 109 [0-209}, PBC; 0 [0-301], ALD; 51 [O-I13}, and NL; 4.2 [0.024-7.9], showing significant reduction of RNase L-I mRNA in CH-C (p=O.OI). Expression levels of 2,5-AS, Rl'llase L, and MxA were not different in above diseases. Conclusions: Among several IFN-inducible proteins, only PKR and RNase L-I showed altered expression patterns in the CH-C liver. While the functionalsignificance of the down-regulation of RNase L-I remains to be elucidated, the overexpression ofPKR mRNAand its correlation with serum ALT values suggests that the PKR system may playa role in the antiviral mechanism against HCV in vivo.