Integrin α2β1 modulates EGF stimulation of Rho GTPase‐dependent morphological changes in adherent human rhabdomyosarcoma RD cells

Abstract

The ability of cells to undergo shape changes is essential for diverse cellular functions including cell growth, differentiation, and movement. The present study examines how an integration of the function of α2β1 integrin with that of the receptor for epidermal growth factor (EGFR) modulates EGF‐stimulated morphological changes in human rhabdomyosarcoma RD transfectant cells. Upon EGF stimulation, RD transfectant cells that lacked α2β1 integrin expression (RDpF) underwent contraction; in contrast, expression of α2β1 on RD cells (RDX2C2) resulted in transient cell spreading. Integrin α2 cytoplasmic domain played a critical role in the observed α2β1‐mediated conversion from a cell rounding to a cell spreading phenotype. Thus, the expression of an α2 cytoplasmic domain deletion variant (X2C0) or a chimeric α2β1 containing the cytoplasmic domain of α4 (X2C4) or α5 (X2C5), instead of α2, failed to mediate spreading upon EGF stimulation. Using dominant negative (DN) mutants of RhoGTPases, results revealed that RhoA activation was required for both EGF‐stimulated responses of cell rounding and spreading, Cdc42 functioned in the re‐spreading of cells after undergoing EGF‐stimulated contraction, and Rac1 was required in α2β1‐mediated RD cell spreading. Therefore, α2β1 integrin function can switch the Rho GTPase‐dependent cell shape changes in RD cells from an EGF‐stimulated cell contraction to a spreading morphology. Together, results show that integrin α2 cytoplasmic domain plays an indispensable role in the ability of integrin α2β1 to modulate EGF stimulation of Rho‐GTPase‐dependent morphological changes in RD cells.