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Moving PKB to the Membrane

Many signaling pathways control cell survival, and it has become apparent that the intracellular localization of some pathway components is critical for their effect. For example, activation of protein kinase B (PKB, also called Akt) protects cells from apoptosis, but this activation process requires two steps--translocation to membranes and then phosphorylation on serine and threonine residues. Fukuda et al. report that the translocation step depends on calponin homology domain-containing integrin-linked (ILK)-binding protein (CH-ILKBP). This adaptor protein interacts with ILK and the cytoskeletal proteins paxillin and actin, and it is found at actin-plasma membrane junctions. Loss of CH-ILKBP expression by interfering RNA treatment of cells did not affect focal adhesion formation or ILK localization to adhesion sites. However, this condition caused a decrease in PKB membrane localization and phosphorylation, yet increased caspase activity and apoptosis. Expression of a myristoylated, constitutively membrane-bound form of PKB in CH-ILKBP-depleted cells restored PKB phosphorylation and rescued cells from apoptosis. Because ILK can phosphorylate PKB and both proteins localize at or near sites of cell-extracellular matrix contact, the authors propose that CH-ILKBP could facilitate localized activation of PKB. T. Fukuda, L. Guo, X. Shi, C. Wu, CH-ILKBP regulates cell survival by facilitating the membrane translocation of protein kinase B/Akt. J. Cell. Biol. 160, 1001-1008 (2003). [Abstract] [Full Text]