Regulation of bcl-2 expression in PLB-985 cells. Northern blots of: (A) cells treated with 1.25% DMSO for 1 hour to 7 days; (B) cells treated with either 9-cis- (lanes 1), 13-cis-(lanes 2), or all-trans-RA (lanes 3) for 1, 2, 3, 4, and 7 days; and (C) cells treated with 9-cis-RA for 1 to 48 hours. Lane C contains control normal cell RNA. (D) Western blot showing downregulation of bcl-2 protein in PLB-985 and NB4 cells treated with 9-cis-RA for 1, 2, 3, 4, and 7 days. Ten micrograms of protein extract was separated on a 15% SDS-PAGE, transferred to a membrane, and probed with an α-bcl-2 antibody using ECL, described in Materials and Methods. Lane C contains control normal cell protein.