SYNERGISTIC ACTIVATION OF RLD-1 BY AGENTS TRIGGERING PKA AND PKC DEPENDENT SIGNALING

RLD-1 and OR-1 are closely related orphan nuclear receptors that can b e activated by certain oxysterols. To obtain cells stably expressing R LD-1 or OR-1, CHOK1 cells were successively transfected with a DGRE2-A LP reporter and GR-RLD-1 or GR-OR-1 chimeric constructs. The selected cell clones that showed low background activity of the reporter and ma ximum fold induction by 22R(OH)cholesterol were used for subsequent ex periments. Treatment of the cells with PGE(2), TPA, or 8-bromo-cAMP al one did not transactivate the reporter, However, the induction of the reporter by 22R(OH)cholesterol was markedly enhanced in the presence o f PGE(2), TPA, 8-bromo-cAMP, or forskolin in cells expressing GR-RLD-1 . The enhancement was inhibited by H-89 and bisindolylmaleimide, both inhibitors of protein kinases. These results suggest that transactivat ion by ligand-activated RLD-1 may be further modulated/regulated throu gh other signal transduction pathways involving phosphorylation cataly zed by protein kinases. (C) 1998 Academic Press.