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Actin cytoskeleton regulates extracellular matrix-dependent survival signals in glomerular epithelial cells

¹Department of Medicine, McGill University Health Centre, Montreal, Quebec; and ²Kidney Research Centre, Department of Medicine, The Ottawa Hospital, University of Ottawa, Ottawa, Ontario, Canada

Submitted 17 March 2005 ; accepted in final form 6 July 2005

Adhesion of rat glomerular epithelial cells (GEC) to collagen activates focal adhesion kinase (FAK) and the Ras-extracellular signal-regulated kinase (ERK) pathway and supports survival (prevents apoptosis). The present study addresses the relationship between actin organization and the survival phenotype. Parental GEC (adherent to collagen) and GEC stably transfected with constitutively active mutants of mitogen-activated protein kinase kinase (R4F-MEK) or FAK (CD2-FAK) (on plastic) showed ERK activation, low levels of apoptosis, and a cortical distribution of F-actin. Parental GEC adherent to plastic showed increased apoptosis, disorganization of cortical F-actin, and formation of prominent stress fibers. Assembly of cortical F-actin was, at least in part, mediated via ERK. However, disruption of the actin cytoskeleton with cytochalasin D or latrunculin B in parental GEC (on collagen) and in GEC that express R4F-MEK or CD2-FAK (on plastic) decreased ERK activation and increased apoptosis. Expression of a constitutively active RhoA (L⁶³RhoA) induced assembly of cortical F-actin, promoted ERK activation, and supplanted the requirement of collagen for survival. Adhesion of GEC to collagen increased phosphatidylinositol-4,5-bisphosphate (PIP₂). Downregulation or sequestration of PIP₂ by transfection with an inositol 5'-phosphatase or the plextrin-homology domain of phospholipase C-1 decreased F-actin content and survival. Moreover, overexpression of wild-type or K256E mutant -actinin-4 with increased affinity for F-actin increased apoptosis. These results demonstrate a reciprocal relationship between collagen-induced cortical F-actin assembly and collagen-dependent survival signaling, including ERK activation. Appropriate remodeling of the actin cytoskeleton may be necessary for facilitating survival, as both disassembly and excessive crosslinking affect survival adversely.

-actinin-4; apoptosis; collagen; extracellular signal-regulated kinase; RhoA

This article has been cited by other articles:

				A. V. Cybulsky, T. Takano, J. Papillon, K. Bijian, J. Guillemette, and C. R. J. Kennedy Glomerular epithelial cell injury associated with mutant {alpha}-actinin-4 Am J Physiol Renal Physiol, October 1, 2009; 297(4): F987 - F995. [Abstract] [Full Text] [PDF]