Fig. 1. A, dose-response relationships for regulation of cyclin D1 protein by 15d-PGJ2 (top), PGA2 (middle), and CP (bottom). *, location of electrophilic carbon atoms. B, effect of 15d-PGJ2 on cyclin D1 protein expression in HeLa and NIH-3T3 cells. Cultures were treated with DMSO vehicle or 10 µM 15d-PGJ2 for 2 h. Protein extracts were prepared and subjected to Western blotting (upper panel). Results were quantified by scanning densitometry (lower panel). Bars, means of three different cultures; ±, SE. C, dose-response for regulation of cyclin D1 protein by hydrogen peroxide (top, triplicate dishes treated with each concentration), sodium arsenite (middle, triplicate dishes treated with each concentration), and UV light (bottom). MCF-7 cells were treated for 1 h with each compound at the indicated concentrations or with UV as described in "Materials and Methods." Extracts were prepared, and the cyclin D1 and ß-actin protein levels were quantified by Western blotting.