Figure 9.

TGFβ inhibits the TSH-induced relocalization of p27^kip1 from cdk2 to cyclin D3–cdk4, but not the assembly of cyclin D3–cdk4 complexes. Quiescent dog thyrocytes were stimulated for 20 h with TSH (1 mU/ml) (T) or EGF (25 ng/ml) + serum (10%) (ES) with or without TGFβ (2 ng/ml) (β) or remained in control (C) condition. Immunoprecipitations (IP) were carried out from equal amounts of cell extracts with antibodies against cyclin D3, cdk4, cdk2, and p27^kip1, followed by separation by SDS-PAGE. The proteins were then transferred to nitrocellulose membranes, followed by Western blotting (WB) with the indicated antibodies. The position of p27^kip1 and the different forms of cdk2 are indicated by arrows in the respective panels.