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Essay On Hbx X Protein

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Hepatitis B virus x protein (HBx) is one of four encoded proteins in the Hepatitis B virus (HBV) genome. HBx is encoded by the smallest open reading frame of mammalian hepadnaviruses which produces a 154-amino acid protein with a molecular mass of 17.5 kDa. HBx has defied high-resolution crystallization and nuclear magnetic resonance so little is known of HBx three-dimensional structure (an implication that HBx is unstructured). HBx also lacks homology with any other known protein so there is poor understanding of how it functions. Comparative analysis of HBx gene sequences from mammalian hepadnaviruses of different species has highlighted areas where the sequence is highly conserved. This includes predicted helical domains located in the …show more content…

Research suggests that when HBx interacts with cellular proteins it dimerizes; however, this remains speculative. Three articles (Gao et al., Elmore et al. and Zhu et al.) have been selected to highlight some of the key carcinogenic effects of the HBx protein.
MicroRNA-145 (miR-145) expression shows an inhibitory effect on the proliferation of human cancer cells. In HCC, the expression of miR-145 was found to be significantly downregulated as a result of HBx interaction. Gao et al. identified Cullin-5 (CUL5) as a target of miR-145. CUL5 has been reported to be functionally involved in numerous cellular activities including the cell cycle. In addition, CUL5 was also reported to be involved in regulating apoptosis by modulating the phosphorylation of mitogen-activated protein kinase (MAPK) and induce p53 mRNA and protein expression. The substantial increase in the expression of CUL5, due to the inhibition of a miRNA-145 expression by HBx, results in less phosphorylation of MAPK and therefore less p53 mRNA and protein expression. This study confirmed a significant decrease in the expression of miRNA-145 and a substantial increase in the mRNA and protein expression of CUL5 in HBx-over-expressing cells compared with empty vector-transfected cells. The proliferation of the cells transfected with HBX plasmid markedly increased compared with cells transfected with empty vector.
The p53 tumor suppressor protein is involved in many cellular

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