Regulation of cadmium-induced apoptosis by PKCδ in U937 human promonocytic cells

Pulse treatment with cadmium chloride followed by recovery caused apoptosis in U937 human promonocytic cells. In addition, the treatrnent-induced, PKC delta translocation from cytosol to membrane fraction, which was already detected at 30 min of treatment; and also caused PKC delta cleavage to give a 41-kDa fragment, which was detected at 3-6 h of recovery, concomitantly with the execution of apoptosis. All these effects were reduced by the PKC delta-specific inhibitor rottlerin. By contrast, rottlerin did not prevent the cadmium-provoked stimulation of the stress response (as measured by HSP70 expression), nor inhibited the generation of apoptosis by heat-shock, which failed to cause PKC delta translocation. Cadmium chloride rapidly induced p38(MAPK) activation, which was not affected by rottlerin. By contrast, the p38(MAPK) inhibitor SB203580 reduced PKC delta translocation and cleavage, indicating that p38(MAPK) activation precedes and regulates PKC delta activation. It is concluded that PKC delta mediates apoptosis induction by cadmium ions via early membrane translocation, and also possibly through late kinase proteolytic cleavage and phosphorylation on tyrosine residues. (c) 2004 Elsevier B.V All rights reserved.