Reduced Expression of DNA Damage Repair Genes High Mobility Group Box1 and Poly(ADP-ribose) Polymerase1 in Inactive Carriers of Hepatitis B Virus Infection-A Possible Stage of Viral Integration

Abstract

High mobility group box1 (HMGB1) and poly(ADP-ribose) polymerase1 (PARP1) proteins repair cellular DNA damage. Reduced expression of the corresponding genes can lead to an impaired DNA damage repair mechanism. Intracellular replication of hepatitis B virus (HBV) in such conditions can favor the integration of viral DNA into host genome leading to the development of hepatocellular carcinoma (HCC). This study was performed to assess the expression of HMGB1 and PARP1 mRNAs in conjunction with the estimation of HBV replication intermediate pregenomic RNA (PgRNA) in various phases of HBV infection. Eighty eight patients and 26 voluntary blood donors as controls were included in the study. Patients were grouped in to acute (AHB; n=15), inactive carriers (IC; n=36), cirrhosis (Cirr; n=25) and hepatocellular carcinoma (HCC; n=12). Serum HBV DNA was quantified by real time polymerase chain reaction (PCR) assay. Expression of HMGB1, PARP1 and PgRNA were evaluated using peripheral blood mononuclear cells (PBMCs) derived RNA by reverse transcription PCR (RT-PCR) and densitometry. Significant reduction of HMGB1 and PARP1 gene expressions (P<0.05) were observed in patients than controls with more explicit decline of PARP1 (P=0.0002). Both genes were significantly downregulated (P<0.001) in ICs than controls. In ICs, HMGB1 was significantly lowered than cirrhosis (P=0.002) and HCC (P=0.0006) while PARP1 declined significantly (P=0.04) than HCC. Level of PgRNA was comparable in all the disease categories. In conclusion, our findings indicate impaired DNA damage repair mechanisms in HBV infected cells of ICs. This, along with low viral load but higher level of PgRNA in this group is suggestive of the diversion of HBV replication pathway that might facilitate viral DNA integration in to host genome. Intrusion of HBV PgRNA reverse transcription in early stage of infection might appear advantageous to thwart the development of HCC.