Regulation of formyl peptide receptor expression and its mRNA levels during differentiation of HL-60 cells.

When incubated with N6-2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP), HL-60 cells expressed formyl peptide receptor (FPR) (as assessed by ligand binding) and FPR transcripts in a time- and concentration-dependent fashion. Experiments using dbcAMP analogs modified at either the C-6 or C-8 position indicated that the process was mediated by a protein kinase A type I, and protein kinase A type I activity was isolated from undifferentiated HL-60 cells by DEAE-Sephacel chromatography. Forskolin mimicked the effects of dbcAMP. Forskolin and dbcAMP-dependent expression of FPR and FPR transcript was inhibited by staurosporine. Retinoic acid (but not retinal or retinol) was capable of inhibiting dbcAMP-dependent expression of FPR mRNA half-life. Dexamethasone enhanced the effects of dbcAMP and blocked the inhibitory effect of retinoic acid on expression of FPR and FPR transcripts. Phorbol 12-myristate 13-acetate (PMA) alone (1.5-15 nM) failed to induce HL-60 to express FPR and FPR transcripts. Low concentrations (1.5 nM) of PMA enhanced the ability of dbcAMP to induce HL-60 cells to express FPR and FPR transcript, whereas high (15 nM) concentrations of PMA inhibited dbcAMP effects. These results indicate that expression of FPR and FPR transcripts by HL-60 cells can be up- and down-regulated by agents that induce HL-60 cells to differentiate and that a "cross-talk" effect exists between protein kinase A and protein kinase C that modulates FPR gene transcription (and receptor expression) by these cells.