Functional Characterisation of Pre-S1/Pre-S2 Deletion Mutants of Hepatitis B virus – Prof Kramvis
Prof Anna Kramvis
- Hepatitis Virus Diversity Research Programme, Department of Internal Medicine, University of the Witwatersrand
- Read Prof Kramvis’ CV
Title of the project
Functional Characterization of Pre-S1/Pre-S2 Deletion Mutants of Hepatitis B Virus isolated from Southern African HCC and HIV patients.
During the course of another study in HBV/HIV infected South Africans, carried out by Masters student Ms Euphodia Makondo, we found five HBV isolates with preS1/preS2 deletions ranging from 11 to 33 codons (Makondo et al, 2012). These deletions mutants are very similar to those we previously described in hepatocellular carcinoma (HCC) patients. This finding has very important implications in the South African context, where HBV/HIV co-infection occurs in 24% of HIV infected individuals, of which 8.7% were HBsAg-positive (overt infection) and the remaining 15.1% were HBsAg-negative (Bell et al, 2012) . These deletion mutants could be a risk factor for the development of HCC in HIV patients, whose lifespan is being increased following the introduction of highly active antiretroviral treatment (HAART). Thus more studies are necessary to follow the development of these mutants in patients prospectively during the course of HAART treatment and to functionally characterize them in tissue culture. Thus we wish to extend our studies, which we initiated using isolates from HCC patients to isolates from HBV/HIV co-infected individuals. By using clones from the different patient groups we will be able to compare the strains and determine whether the strains from the HIV patients pose a risk factor to the development of HCC in HIV infected individuals. The objective of the proposed extension of our study is to determine the significance of these mutant isolates of HBV by functionally characterizing them in tissue culture. Replication competent clones of both wild-type strains have been constructed and we are busy introducing the preS1/preS2 deletion mutant into these clones. These will be used to transfect liver cells in tissue culture. We will monitor viral replication, surface protein expression and retention at various times posttransfection.
Depending on the outcome of these experiments we will determine whether the mutant virus can cause apoptosis and disturb the unfolded protein response of the cells. We would also like to extend the study to determine whether the proteins expressed by the mutants differ from those expressed by wild-type strains, in terms of the immunological response they elicit. Moreover, if the envelope proteins expressed differ antigenically it is possible to design diagnostics tests to differentiate between the wild-type and mutant strains.