Protein Kinase Cδ Suppresses Autophagy to Induce Kidney Cell Apoptosis in Cisplatin Nephrotoxicity

Nephrotoxicity is a major adverse effect in cisplatin chemotherapy, and renoprotective approaches are unavailable. Recent work unveiled a critical role of protein kinase C δ (PKC δ ) in cisplatin nephrotoxicity and further demonstrated that inhibition of PKC δ not only protects kidneys but enhances the chemotherapeutic effect of cisplatin in tumors; however, the underlying mechanisms remain elusive. Here, we show that cisplatin induced rapid activation of autophagy in cultured kidney tubular cells and in the kidneys of injected mice. Cisplatin also induced the phosphorylation of mammalian target of rapamycin (mTOR), p70S6 kinase downstream of mTOR, and serine/threonine-protein kinase ULK1, a component of the autophagy initiating complex. In vitro , pharmacologic inhibition of mTOR, directly or through inhibition of AKT, enhanced autophagy after cisplatin treatment. Notably, in both cells and kidneys, blockade of PKC δ suppressed the cisplatin-induced phosphorylation of AKT, mTOR, p70S6 kinase, and ULK1 resulting in upregulation of autophagy. Furthermore, constitutively active and inactive forms of PKC δ respectively enhanced and suppressed cisplatin-induced apoptosis in cultured cells. In mechanistic studies, we showed coimmunoprecipitation of PKC δ and AKT from lysates of cisplatin-treated cells and direct phosphorylation of AKT at serine-473 by PKC δ in vitro . Finally, administration of the PKC δ inhibitor rottlerin with cisplatin protected against cisplatin nephrotoxicity in wild-type mice, but not in renal autophagy–deficient mice. Together, these results reveal a pathway consisting of PKC δ , AKT, mTOR, and ULK1 that inhibits autophagy in cisplatin nephrotoxicity. PKC δ mediates cisplatin nephrotoxicity at least in part by suppressing autophagy, and accordingly, PKC δ inhibition protects kidneys by upregulating autophagy.