Analysis of the cell cycle in vitamin A– and Arovit-treated MSCs.

(A) Cyclin E, cyclin A, p27^Kip1, p21^Cip1, and actin immunoblotting analyses of 48 hours of vitamin A–treated MSCs. The concentration of all-trans-retinol used in the experiment was 40 μM. Protein (20 μg) was used for actin, cyclin, and p27^Kip1immunoblotting, whereas 80 μg protein was used for p21^Cip1. At the bottom of each immunoblot the relative amount of the signals (control is assumed as 1.0) determined by laser scanning. (B) Cdk2 was immunoprecipitated from equal amounts of cellular extracts (500 μg) as reported in “Patient, materials, and methods.” Identical aliquots of the immunoprecipitated materials were assayed for the kinase activity (Cdk2 activity) and for the cdk2 total contents by immunoblotting (Cdk2).