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CH-ILKBP regulates cell survival by facilitating the membrane translocation of protein kinase B/Akt
Tomohiko Fukuda,
Lida Guo,
Xiaohua Shi, and
Chuanyue Wu
Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15261
Address correspondence to Chuanyue Wu, 707B Scaife Hall, Dept. of Pathology, University of Pittsburgh, 3550 Terrace St., Pittsburgh, PA 15261. Tel.: (412) 648-2350. Fax: (509) 561-4062. E-mail: carywu{at}pitt.edu
Abstract:
Cell survival depends on proper propagation of protective signalsthrough intracellular signaling intermediates. We report herethat calponin homology domaincontaining integrin-linkedkinase (ILK)binding protein (CH-ILKBP), a widely expressedadaptor protein localized at plasma membrane-actin junctions,is essential for transmission of survival signals. Cells thatare depleted of CH-ILKBP undergo extensive apoptosis despitethe presence of cellextracellular matrix contacts andsoluble growth factors. The activating phosphorylation of proteinkinase B (PKB/Akt), a key regulator of apoptosis, is impairedin the absence of CH-ILKBP. Importantly, loss of CH-ILKBP preventsthe membrane translocation of PKB/Akt. Furthermore, forced membranetargeting of PKB/Akt bypasses the requirement of CH-ILKBP forthe activating phosphorylation of PKB/Akt, suggesting that CH-ILKBPis required for the membrane translocation but not the subsequentphosphorylation of PKB/Akt. Finally, we show that loss of CH-ILKBPis also required for the full activation of extracellular signalregulatedkinase (ERK)1/2. However, restoration of the PKB/Akt activationis sufficient for protection of cells from apoptosis inducedby the depletion of CH-ILKBP despite the persistent suppressionof the ERK1/2 activation. Thus, CH-ILKBP is an important componentof the prosurvival signaling pathway functioning primarily byfacilitating the membrane translocation of PKB/Akt and consequentlythe activation of PKB/Akt in response to extracellular survivalsignals.
Key Words: apoptosis; CH-ILKBP; protein kinase B/Akt; membrane translocation; ILK
* Abbreviations used in this paper: CH-ILKBP, calponin homologydomaincontaining ILK-binding protein; ERK, extracellularsignalregulated kinase; IGF, insulin-like growth factor;ILK, integrin-linked kinase; PKB, protein kinase B; RNAi, RNAinterference; siRNA, small interfering RNA.
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