Mutations within the hamster polyomavirus large T antigen domain involved in pRb binding impair virus productive cycle and immortalization capacity
Goutebroze, L.; de la Roche Saint Andre, C.; Scherneck, S.; Feunteun, J.
Oncogene 8(3): 685-693
1993
ISSN/ISBN: 0950-9232 PMID: 8382359 Document Number: 406569
Hamster polyomavirus (HaPV) causes lymphoma and leukemia when injected into newborn Syrian hamsters and achieves full tranformation of rodent fibroblasts in vitro. It offers a comprehensive model to study at a molecular level the contributions of the viral oncogenes to neoplastic transformation in vitro and in the animal. We have investigated the ability of HaPV large T antigen to form a complex with the product of the retinoblastoma gene (pRb) in vitro. In this report, we demonstrate that HaPV large T antigen can indeed complex the pRb polypeptide. In order to investigate to what extent this interaction might contribute to tumor inducion by the virus, we have introduced two different point mutations within the putative pRb-binding sequence of large T antigen, and as a preliminary to in vivo experiments we have studied their effects in vitro on some biological activities relevant to tumor induction. We show that the substitution (Glu-134 fwdarw Lys) obliterates pRb binding, suggesting that Glu-134 participates in the interactions between pRb and large T antigen, whereas the substitution (Glu-135 fwdarw Lys) has no effect. The Lys-134 mutation is strongly deletrious to the immortalization capacity of the viral genome, whereas the Lys-135 mutation has no effect. Neither of the two mutations affects the capacity of the viral genome to induce foci formation in the rat established cell line F111. These results indicate that the interaction between large T and pRb is required in the immortalization process but irrelevant to transformation. Both mutants show at least partial impairment of replication and productive cycle.