EFFECT OF STAUROSPORINE ON FMET-LEU-PHE-STIMULATED HUMAN NEUTROPHILS - DISSOCIATED RELEASE OF INOSITOL 1,4,5-TRISPHOSPHATE, DIACYLGLYCEROL AND INTRACELLULAR CALCIUM

Staurosporine, a microbial alkaloid, enhances inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DG) production rapidly and dose-dependently in fMet-Leu-Phe (FMLP)-stimulated human neutrophils showing maximal effects at 1-mu-M concentration. The IP3 increase was specific for staurosporine as three other putative protein kinase C (PKC) inhibitors, H7, sphingosine and palmitoylcarnitine were unable to enhance the IP3 generation in FMLP-stimulated human neutrophils. Staurosporine, at concentrations 0.3-1.0-mu-M, did not affect the initial mobilization of FMLP-induced intracellular Ca2+ (Ca(i)2+), although a sustained elevation of cytosolic Ca2+ level was observed within 5 min. This effect could not be suppressed, even by 1-mu-M phorbolmyristate 12,13-acetate (PMA). Whereas lower concentrations of staurosporine (less-than-or-equal-to 100 nM) were unable to affect FMLP-induced IP3 production, DG accumulation and Ca(i)2+, the PMA-inhibited initial Ca(i)2+ signal and IP3 formation triggered by FMLP were almost completely restored. At higher concentrations (greater-than-or-equal-to 300 nM) staurosporine reversed the inhibitory effect of other protein kinases, distinct from the PMA-inducible one, which may be responsible for the phosphatidyl inositol 4,5-bisphosphate (PIP2) breakdown, thus causing accumulation of IP3 and DG and an elevation of Ca(i)2+ level. Whereas IP3 declined to basal level within 5 min, the DG level remained elevated during the same period. This phenomenon is attributed to phospholipase D (PLD) stimulation by staurosporine, which augments the DG synthesis, in part through PA degradation via phosphatidic acid (PA) phosphohydrolase.