Hepatitis B virus genotype A rarely circulates as an HBe-minus mutant: possible contribution of a single nucleotide in the precore region

Abstract

The emergence of HBe-minus hepatitis B virus (HBV) mutants, usually through a UAG nonsense mutation at codon 28 of the precore region, helps the virus to survive the anti-HBe immune response of the host. Host and viral factors that predispose to the emergence of such mutants are not well characterized. The fact that the precore region forms a hairpin structure essential for the packaging of viral pregenomic RNA may explain the extremely high prevalence of the UAG mutation at codon 28. It converts a wobble U-G pair in the packaging signal between nucleotide 3 of codon 15 (CCU) and nucleotide 2 of codon 28 (UGG) into a U-A pair. Since genotype A of HBV has a CCC sequence at codon 15, the UAG mutation would, instead, disrupt a C-G pair present in the wild-type virus. This alteration was shown by transfection experiments to greatly compromise the packaging of pregenomic RNA. The implication of this finding was elucidated by molecular epidemiological studies. Genotype A was found to be the most prevalent genotype in the wild-type virus populations in France but was found in only 1 of the 46 isolates of HBe-minus mutants found there. These mutants were contributed chiefly by genotype D, the second most prevalent genotype in France, which is characterized by a CCU sequence at codon 15. The role of the single nucleotide at codon 15 was confirmed by the finding of the single genotype A isolate in which both wild-type and mutant viruses were present. Interestingly, nearly all of the mutants had a codon 15 sequence of CCU instead of the CCC present in the wild-type viruses. Our results suggest that genotype A of HBV rarely circulates as HBe-minus mutants, probably because of a requirement for a simultaneous sequence change at codon 15. These data, together with the virtual absence of genotype A in the Chinese samples examined, may provide some insights into the uneven prevalence of HBe-minus mutants in the world.

Genotype prevalence, viral load and outcome of hepatitis B virus precore mutant infection in stable patients and in patients after liver transplantation

“…Genotypes A and C were observed in only a few patients, from Western Europe and Asia respectively. These results agree with studies on the worldwide distribution of viral genotypes (14,20,21), and on viral genotype frequencies (14,(19)(20)(21). In our sample, the prevalence of the core promoter region mutation and the stop codon 28 mutation were similar in the transplant and stable groups, suggesting that these mutations are not associated with liver disease activity in patients infected with the precore mutant.…”

“…Mean serum ALT level at last follow-up was 51.8 ± 30.1 U/L, and mean HBV DNA level was 510 · 10 3 ± 1240 · 10 3 copies/mL. Four of seven lamivudine-treated patients (57.1%) developed lamivudine resistance within a median of 16 months (range [11][12][13][14][15][16][17][18][19][20][21][22]. Among the whole stable group, five (16.1%) developed liver failure, of whom two are livertransplant candidates.…”

Exploring the Biological Basis of Hepatitis B E Antigen in Hepatitis B Virus Infection

“…2). 14,15 Chronic Infection. HBV variants that do not produce HBeAg were first described in individuals with chronic HBV infection who underwent spontaneous conversion to anti-HBe and inactive liver disease.…”

Is Lamivudine Effective on Precore/Core Promoter Mutants of Hepatitis B Virus?

“…3 In clinical practice, the most frequently encountered variant form of chronic HBV infections, is the hepatitis B e antigen (HBeAg)-negative chronic hepatitis B associated with the replication of precore stop codon mutants that terminate pre-C/C protein and HBeAg expression 5 and are tightly dependent on viral genotypes. 6 Such variants are selected during seroconversion from HBeAg to anti-HBe and are responsible for HBeAg-negative chronic hepatitis B, which represents up to 50% to 95% of the chronic hepatitis B cases followed in liver units in Europe with an increasing prevalence from north to south. 7,8 Other mutants in the core promoter region have been identified independently of viral genotypes in both HBeAg-positive and -negative patients and were shown to down-regulate the transcription of the precore promoter messenger RNA and therefore decrease the expression of the HBeAg.…”