Mechanical and Chemical Regulation of Endothelial Cell Polarity

Abstract

See related article, pages 939–946 McCue et al1 showed by a combination of in vitro and in vivo studies that shear stress regulates planar cell polarity (PCP) of endothelial cells (ECs) and that glycogen synthase kinase 3β (GSK3β) plays a significant role in this process. The application of shear stress at 15 dyn/cm2 to cultured porcine aortic ECs caused tubulin acetylation and stabilization of microtubules (MTs), downstream polarization of microtubule-organizing centers (MTOCs), as well as MT orientation and EC elongation in the shear direction. The importance of tubulin dynamics in these shear-induced changes was demonstrated by their elimination by the MT-disrupting agent nocodazole and also the MT-stabilizing agent taxol. A novel finding is the role of GSK-3β in shear-induced MT orientation. GSK-3β is a regulatory serine/threonine kinase2 that has high activity under basal state, and its activity is inhibited after serine-9 phosphorylation (p-GSK-3β); this would lead to downstream signaling3 and MT stabilization,4 eg, through the binding of adenomatous polyposis cell protein (APC).4,5 GSK-3β can be inhibited by lithium and SB415286, which interfere with the binding of ATP to GSK-36 rather than acting directly on GSK-3 phosphorylation. The evidence that GSK-3β plays a role in mediating the shear-induced MT orientation and cell shape change is as follows. First, shear stress caused an increase in p-GSK-3β (at 1 and 4 hours, though waned at 24 hours). Second, inhibition of GSK-3β by LiCl and SB415286 blocked the shear-induced EC elongation. SB415286 was also shown to reverse the shear-induced downstream localization of MTOCs to become upstream. Third, overexpression of a constitutively active GSK-3β (GSKS9A), which cannot be phosphorylated, attenuated tubulin acetylation, blocked cell elongation, and caused MTOC distribution to be more random. Although these results provide evidence that the shear-induced PCP and cell elongation are …