Figure 9.

GFP-TAM67 expression inhibits activation of both cyclin D1 and cyclin E kinase complexes and induces p21^CIP1/WAF1. The iGT1a cells were treated with and without 10 μM ponasterone A for 24 h. (A) Cyclin E immunoprecipitates were assayed for histone H1 kinase activity, blotted, and probed with antibodies to cyclin E and p21^CIP1/WAF1. (B) Cyclin D1 immunoprecipitates were assayed for retinoblastoma protein kinase activity, blotted, and probed with antibodies to cyclin D1 and p21^CIP1/WAF1. (C) Immunoblots of cell lysates from iGT1a cells treated with 0 or 10 μM ponasterone A and probed with antibodies to cdc25a and cdk7. (D) Northern blot analysis of 5 μg of total RNA isolated from iGT1a cells treated with 0 or 10 μM ponasterone A and probed with the indicated cDNAs.