THE MDM2 C-TERMINAL REGION BINDS TO TAF(II)250 AND IS REQUIRED FOR MDM2 REGULATION OF THE CYCLIN-A PROMOTER

MDM2 proto-oncogene expression is aberrant in many human tumors. Its n ormal role is to modulate the functions of p53. The N terminus of MDM2 interacts with p53, whereas the properties of the rest of the molecul e are poorly understood. We show that MDM2 binds to the general transc ription factor TFIID in vivo. The C-terminal Ring finger interacts wit h TAF(II)250/CCG1, and the central acidic domain interacts with TBP. E xpression of MDM2 activates the cyclin A gene promoter but not c-fos, showing that the effects of MDM2 are specific. Deletion of the C-termi nal region of MDM2 abolishes activation, showing that the C-terminal d omain of MDM2 is functionally important. We found that increasing MDM2 expression to higher levels inhibits the cyclin A promoter. Inhibitio n appears to result from titration of general transcription factors be cause MDM2 overexpression inhibits c-fos as well as other promoters in vivo and basal transcription in vitro. The mechanisms of repression o f the cyclin A and fos promoters appear to be different. Cyclin A repr ession is lost by deleting the C terminus, whereas that of c-fos is lo st by removal of the acidic domain, These results reinforce the conclu sion that the C terminus of MDM2 mediates effects on the cyclin A prom oter, MDM2 transformed cells contain elevated levels of cyclin A mRNA, showing that activation occurs under physiological conditions. There is a positive correlation between MDM2 binding to TAF(II)250 and MDM2 activation of the cyclin A promoter. The C-terminal region of MDM2, wh ich contains the Ring finger, interacts with TAF(II)250 and is require d for regulation of the cyclin A promoter by MDM2. Our results link th e activity of MDM2, a transforming protein implicated in many human tu mors, with cyclin A, a regulator of the cell cycle.