Interaction of adeno-associated virus Rep78 with SV40 T antigen: implications in Rep protein expression leading to the inhibition of SV40-mediated cell proliferation.

Adeno-associated virus (AAV) type 2 is a nonpathogenic human parvovirus that is dependent on a helper virus, usually adenovirus, for its replication. The left half of AAV encodes the multifunctional nonstructural proteins required for replication of its DNA. Here, we present evidence that SV40 provides a helper function for the expression of AAV Rep protein, as demonstrated by Western blot analysis of cell extracts from SV40-transformed human fibroblasts infected with AAV. We also show, using a luciferase reporter system, that SV40-mediated transcriptional transactivation of 'S'-phase genes is substantially inhibited by the presence of AAV. Because the SV40 T antigen is critical to oncogenicity and cellular DNA proliferation, we investigated its interaction with AAV Rep protein. The physical interaction between these two molecules was confirmed by electrophoretic mobility supershift assay and affinity chromatography. These results show, for the first time, the possible molecular mechanisms behind the AAV-mediated inhibition of SV40 oncogenicity and provide the basis for further investigation into the direct and indirect role of AAV Rep in controlling viral transforming activity. Copyright 2002 S. Karger AG, Basel