Figure 9.

Spy1-enhanced proliferation is dependent on endogenous p27. (A) MEF–/– cells were transfected with the indicated constructs, medium was changed 24 h posttransfection, and cells were counted via trypan blue exclusion 48 h posttransfection. The graphed data indicate that exogenous p27 slows proliferation in the MEF–/– cells and that Spy1 can overcome this inhibition of proliferation. Spy1 does not enhance proliferation over mock control in cells lacking endogenous p27. The data are one representative experiment of four. Error bars indicate the SEM of three separate transfections. (B) Lysates were analyzed by 10% SDS-PAGE, transferred to nitrocellulose membrane, and immunoblotted with α-myc-Spy1, and α-p27 sera to demonstrate protein expression. (C) Endogenous Spy1 was immunoprecipitated from either NIH3T3 cells null for p27 (3T3–/–) or NIH3T3 wt (3T3wt). Both lysate and immunoprecipitated samples were separated by 10% SDS-PAGE and immunoblotted with α-CDK2 sera (top panel) or α-p27 sera (bottom panel). (D) Endogenous CDK2 was immunoprecipitated from both 3T3wt and 3T3–/– cell types. Lysate samples and the immunoprecipitated samples were analyzed by 10% SDS-PAGE, and immunoblotting was carried out with α-Spy1 sera.