SV40 large T antigen promotes dephosphorylation of p130.
SV40 large T antigen (Ag) binds to all members of the retinoblastoma (RB) tumor suppressor family including pRb, p107, and p130. Although the LXCXE motif of T Ag binds directly to the RB proteins, it is not sufficient to fully inactivate their function. The N-terminal DNA J domain of T Ag cooperates with the LXCXE motif to override RB-mediated repression of E2F-dependent transcription. In addition, T Ag can reduce the overall phosphorylation state of p107 and p130 that is dependent on an intact J domain and LXCXE motif. However, the mechanism of this activity has not been described. Here we describe the use of a cell-free system to characterize the effect of T Ag on p130 phosphorylation. When incubated in extracts prepared from S phase cells, p130 undergoes specific phosphorylation. Addition of T Ag to S phase extracts leads to a reduction of p130 phosphorylation in vitro. The ability of T Ag to reduce the phosphorylation of p130 in vitro is dependent on an intact DNA J domain and can be inhibited by okadaic acid and PP2A-specific inhibitors. These results suggest that T Ag recruits a phosphatase activity in a DNA J domain-dependent manner to reduce the phosphorylation of p130.
Lin
Jennifer Y
JY
Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA.
DeCaprio
James A
JA
D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002474:Cell-Free System; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D009154:Mutation; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D011506:Proteins; D050717:Retinoblastoma-Like Protein p130; D016196:S Phase
D000952:Antigens, Polyomavirus Transforming; D004791:Enzyme Inhibitors; D010750:Phosphoproteins; D011506:Proteins; C493837:RBL2 protein, human; D050717:Retinoblastoma-Like Protein p130; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases