RETINOID MODULATION OF C-MYC AND MAX GENE-EXPRESSION IN HUMAN BREAST-CARCINOMA

Retinoic acid (RA). modulation of c-myc and max gene expression was in vestigated in human breast carcinoma (HBC) cell lines. Our results dem onstrate that c-myc and max genes are differentially expressed in HBC cells which was accompanied by increases in [H-3]-thymidine incorporat ion and percent of cells in the S phase of cell cycle. RA-mediated inc rease in c-myc mRNA levels were noticed as early as 30 min. and maximu m levels were attained by 1 h. RA effect on max mRNA levels was slow a nd gradual with the maximum effect noticed by 48 h. Nuclear run-on ass ays demonstrated that RA mediated its effect by increasing the rate of transcription of both of these genes. We thus report for the first ti me that RA, during its growth inhibitory effects on MCF-7 HBC cells, p ositively regulates the gene expression of c-myc and max.