In this study, we investigated the putative roles of certain protein kinase C (PKC) isoenzymes in the regulation of proliferation and arachidonic acid (AA) release in the human monocytoid MonoMac-6 cell line. Experiments employing specific PKC inhibitors and molecular biological methods (RNA-interference, recombinant overexpression) revealed that the two dominantly expressed isozymes, i.e., the "conventional" cPKCbeta and the "novel" nPKCdelta, promote AA production and cellular proliferation. In addition, using different phospholipase A(2) (PLA(2)) inhibitors, we were able to show that the calcium-independent iPLA(2) as well as diacylglycerol lipase (but not the cytosolic PLA(2)) function as "downstream" targets of cPKCbeta and nPKCdelta. In addition, we have also found that, among the other existing PKC isoforms, cPKCalpha plays a minor inhibitory role, whereas nPKCvarepsilon and aPKCzeta apparently do not regulate these cellular processes. In conclusion, in this paper we provide the first evidence that certain PKC isoforms play pivotal, specific, and (at least partly) antagonistic roles in the regulation of AA production and cellular proliferation of human monocytoid MonoMac-6 cells.