EFFECT OF A SELECTIVE PROTEIN-KINASE-C INHIBITOR, RO-31-8425, ON MAC-1 EXPRESSION AND ADHESION OF HUMAN NEUTROPHILS

The role of protein kinase C (PKC) in mediating up-regulation of macro phage 1 adhesion protein (Mac-1) and adhesion of neutrophils in respon se to physiological agonists is not clear. Previous studies have relie d on use of phorbol esters to activate PKC directly or on results obta ined with non-selective inhibitors of protein kinases. 10-yl]-4-(1-met hyl-3-indolyl)-1H-pyrrole-2,5-dione hydrochloride (Ro 31-8425) is a po tent and highly selective inhibitor of PKC (Bit et al. J. Med. Chem. 1 993. 36: 21). In these studies Ro 31-8425 has been used to define, mor e definitively, the role of PKC in mediating complement fragment C5a ( C5a)-stimulated upregulation of Mac-1 and adhesion of neutrophils to e ndothelial cells and to bovine serum albumin (BSA)-coated plastic. Pho rbol 12, 13 dibutyrate (PBu(2)) increased surface expression of Mac-1 and stimulated adhesion of neutrophils to endothelial cells and to BSA -coated plastic. This confirms previous reports that activation of PKC can stimulate these responses. The PKC inhibitor, Ro 31-8425, inhibit ed the PBu(2)-stimulated responses, which confirms that Ro 31-8425 was effective in inhibiting PKC in these neutrophils. A more physiologica l agonist, C5a, also increased surface expression of Mac-1 and adhesio n of neutrophils to endothelial cells and BSA-coated plastic. However, the responses to C5a were unaffected by Ro 31-8425. These results sug gest that, although activation of PKC can promote up-regulation of Mac -1 and adhesion of neutrophils, this does not appear to be the physiol ogical pathway. A non-selective protein kinase inhibitor, staurosporin e, inhibited both PBu(2) and C5a-stimulated adhesion. This suggests th at a protein kinase other than PKC, possibly a tyrosine protein kinase , is likely to be involved in mediating C5a-stimulated Mac-1 up-regula tion and adhesion. These results emphasise the need for caution in int erpreting experiments and assuming a role for PKC. Use of a potent and selective inhibitor of PKC, Ro 31-8425, provides more definitive info rmation.