aPKC-PAR complex dysfunction and tight junction disassembly in renal epithelial cells during ATP depletion.

Renal ischemia and in vitro ATP depletion result in disruption of the epithelial tight junction barrier, which is accompanied by breakdown of plasma membrane polarity. Tight junction formation is regulated by evolutionarily conserved complexes, including that of atypical protein kinase C (aPKC), Par3, and Par6. The aPKC signaling complex is activated by Rac and regulated by protein phosphorylation and associations with other tight junction regulatory proteins, for example, mLgl. In this study, we examined the role of aPKC signaling complex during ATP depletion and recovery in Madin-Darby canine kidney cells. ATP depletion reduced Rac GTPase activity and induced Par3, aPKCzeta, and mLgl-1 redistribution from sites of cell-cell contact, which was restored following recovery from ATP depletion. Zonula occludens (ZO)-1 and Par3 phosphorylation was reduced and association of aPKCzeta with its substrates Par3 and mLgl-1 was stabilized in ATP-depleted Madin-Darby canine kidney cells. ATP depletion also induced a stable association of Par3 with Tiam-1, a Rac GTPase exchange factor, which explains how aPKCzeta and Rac activities were suppressed. Experimental inhibition of aPKCzeta during recovery from ATP depletion interfered with reassembly of ZO-1 and Par3 at cell junctions. These data indicate that aPKC signaling is impaired during ATP depletion, participates in tight junction disassembly during cell injury and is important for tight junction reassembly during recovery.