Objective: All-trans-retinoic acid (RA) regulates cellular growth, differentiation and apoptosis in human prostate by binding to RA receptors. Non-genomic retinoid effects on signal transduction kinases in the cytoplasm are also described in several cells but they are still unknown in prostate cells.
Methods: Using an epithelial cell line derived from normal human prostate (EPN), and normal (NPEC) and malignant (CPEC) epithelial primary cultures of human prostate, we have examined effects of RA on both extracellular signal-regulated kinase 1/2 (Erk1/2) and cAMP accumulation. Then we have verified the effect of the inhibition of Erk1/2 on RA-induced growth arrest and apoptosis in malignant cells.
Results: In NPEC and in EPN treated with RA for up to 24 h, Western blot analyses of Erk1/2 phosphorylation show that RA causes a rapid activation of Erk1/2 within 5 min, which is maintained for 30 min, followed by a return to basal levels. In CPEC, the activated phosphorylation levels persist up to 24 h. While basal cAMP levels are not affected by 30 min treatment with RA in both EPN and NPEC, levels are increased in CPEC. Forskolin-induced cAMP levels are decreased by RA in all cell types. CPEC were incubated for up to 96 h with RA with and without the inhibitor of Erk1/2, UO126. CPEC incubated with RA and UO126 for 72 h showed a significant arrest of cell growth and after 96 h apoptosis in 11% of cells.
Conclusions: We show rapid effects of RA on cytoplasmic messenger pathways in human prostate, and that responses can differ between normal and malignant cells. The inhibition of these pathways could improve the efficiency of RA in prostate cancer growth control.