AMP-activated protein kinase (AMPK), a known regulator of cellular and systemic energy balance, is now recognized to control cell division, cell polarity and cell migration, all of which depend on the actin cytoskeleton. Here we report the effects of A769662, a pharmacological activator of AMPK, on cytoskeletal organization and signalling in epithelial Madin-Darby canine kidney (MDCK) cells. We show that AMPK activation induced shortening or radiation of stress fibers, uncoupling from paxillin and predominance of cortical F-actin. In parallel, Rho-kinase downstream targets, namely myosin regulatory light chain and cofilin, were phosphorylated. These effects resembled the morphological changes in MDCK cells exposed to hyperosmotic shock, which led to Ca2+-dependent AMPK activation via calmodulin-dependent protein kinase kinase-beta(CaMKK beta), a known upstream kinase of AMPK. Indeed, hypertonicity-induced AMPK activation was markedly reduced by the STO-609 CaMKK beta inhibitor, as was the increase in MLC and cofilin phosphorylation. We suggest that AMPK links osmotic stress to the reorganization of the actin cytoskeleton. (C) 2010 Elsevier Inc. All rights reserved.