Modulation of cellular processes by H7, a non-selective inhibitor of protein kinases

Abstract

H7 has been described as a potent inhibitor of protein kinase C (PKC) and has been widely used to investigate the regulatory role of this enzyme in intact cell systems. In this comparative study between H7 and the microbial alkaloid, staurosporine, we found that the former inhibited rat brain PKC and cAMP dependent protein kinase with IC₅₀ values of 18 and 16 μM respectively whereas the latter was a much more potent inhibitor of both kinases with IC₅₀ values of 9.5 nM and 42 nM respectively. H7, at concentrations up to 100 μM, failed to block cellular events induced by phorbol esters, agents which specifically stimulate PKC, yet was a potent inhibitor of IL-2 induced T cell proliferation with an IC₅₀ value of 19 μM. In contrast, staurosporine was a potent inhibitor of both phorbol ester induced p47 phosphorylation in platelet (I₅₀ value=540 nM) and also CD3 and CD4 down-regulation in T cells (I₅₀ values 200 nM and 50 nM respectively). Staurosporine was also a potent inhibitor of IL-2 induced T cell proliferation I₅₀ value=9 nM). These results provide a strong argument against the use of H7 to probe for PKC involvement in cellular processes.