INHIBITION OF THE CALCIUM STORE-OPERATED CALCIUM-ENTRY PATHWAY BY CHEMOTACTIC PEPTIDE AND BY PHORBOL ESTER DEVELOPS GRADUALLY AND INDEPENDENTLY ALONG DIFFERENTIATION OF HL-60 CELLS

N-Formyl-methionyl-leucyl-phenylalanine (fMLP) inhibited transiently t he entry of Ca2+ and Mn2+ induced by emptying with thapsigargin the Ca 2+ stores of HL60 cells differentiated toward granulocytes. Phorbol 12 ,13-dibutyrate (PDB) produced a permanent inhibition of this store-ope rated Ca2+ entry pathway (SOCP), suggesting that inhibition was due to protein phosphorylation mediated by protein kinase C (PKC). Inhibitio n by PDB was prevented by the PKC inhibitors staurosporin and cheleryt hrine. Inhibition by fMLP was prevented by chelerythrine but only part ially by staurosporin. The characteristics of the inhibition were simi lar to those reported in human neutrophils (Montero, M., Alvarez, J., and Garcia-Sancho, J. (1993) J. Biol. Chem. 268, 13055-13061). Neither fMLP nor PDB inhibited significantly SOCP in undifferentiated HL60 ce lls. Single-cell [Ca2+]i measurements at different stages of different iation showed that inhibition by fMLP and PDB developed independently, suggesting different inhibitory mechanisms. The simplest explanation would be that inhibition by fMLP takes place through activation of a p rotein kinase distinct from PKC and that the PDB-activated PKC isoform necessary to phosphorylate and inhibit SOCP is expressed only along d ifferentiation. Additionally, inhibition by both fMLP and PDB develope d gradually. At intermediate stages of differentiation, PDB was able t o produce a partial and maintained inhibition and fMLP a partial and s hort-lived inhibition of SOCP.