Cloning and Mutational Analysis of HBx Gene from the blood of HBV Infected Patients

Abstract

Hepatocellular carcinoma has various etiological agents one of the main one being the chronic persistent infection of Hepatitis B virus. Various studies have speculated the oncogenic potential of its HBx gene and hence its role in development of HCC. The HBx induced carcinogenesis is a result of modulation of various signaling pathways and factors. It has been frequently reported that point mutations and truncations in HBx gene are significantly associated with its oncogenic role and transactivation function and these mutations accumulate in the HBV genome during its natural history of infection. These can be preferentially detected to determine the advancement of disease. This study was designed to investigate the variants of HBx gene amplified through PCR from HBV DNA isolated from 50 patients infected with HBV. The purified products were sequenced and aligned with consensus X sequence to determine the prevalent mutations at nucleotide and protein level. The results indicated higher frequency of mutations at the 3’ and 5’ ends of the gene whereas the internal regions were found to be relatively conserved. Among other important changes, the most frequently occurring mutations included substitutions at 76T→C/A, 97T→C, 303A→T, 400C→T/G, 136C→T and 70G→A/T which resulted in frameshift mutation in X protein, hence disrupting the dimerization domain of protein. Insertions 68_69insAA and 101_102insA were found to cause a frameshift in the respective X protein, hence likely to disrupt its 14-3-3 binding motif. Another deletion 415_416delCA, observed in 4 sequences, caused a frameshift mutation thereby affecting the p53 binding domain of X protein.