pRB-dependent, J domain-independent function of simian virus 40 large T antigen in override of p53 growth suppression.
Simian virus 40 (SV40) large T antigen (LT) can immortalize and transform many cell types. These activities are attributed in large part to the binding and functional inactivation by LT of two major tumor suppressors: p53 and the retinoblastoma protein, pRB. Most effects of LT on pRB have been shown to additionally require an intact J domain, which mediates binding to Hsc70. We show here that the J domain is not required for p53 override in full-length LT. Although LT binds p53, it was shown previously that overcoming a p53-induced cell cycle arrest requires binding to pRB family members (R. S. Quartin et al., J. Virol. 68:1334-1341). We demonstrate that an LT mutant defective for pRB family member binding (K1) can be complemented for efficient override of p53 arrest by a construct encoding the first 135 amino acids of LT with a J domain-inactivating mutation, H42Q. Hence, complementation does not require the J domain, and pRB binding by LT is important for more than dissociating pRB-E2F complexes, which is J dependent. In accordance with this notion, LT alleviates pRB small-pocket-mediated transcriptional repression independently of the J domain. The LT K1 mutant can also be complemented for p53 override by small t antigen (st) in a manner independent of its J domain. Our observations underscore the importance of multiple SV40 functions, two in LT and one in st, that act cooperatively to counteract p53 growth suppression.
Gjoerup
O
O
Department of Cancer Biology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA.
Chao
H
H
DeCaprio
J A
JA
Roberts
T M
TM
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000502:physiology*; D001665:Binding Sites; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D002472:Cell Transformation, Viral / Q000502:physiology; D005816:Genetic Complementation Test; D006801:Humans; D016296:Mutagenesis; D051381:Rats; D016160:Retinoblastoma Protein / Q000502:physiology*; D013696:Temperature; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D000952:Antigens, Polyomavirus Transforming; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53