The Rho Guanine Nucleotide Exchange Factor Syx Regulates the Balance of Dia and ROCK Activities To Promote Polarized-Cancer-Cell Migration

Abstract

The role of RhoA in promoting directed cell migration has been complicated by studies showing that it is activated both in the front and the rear of migrating cells. We report here that the RhoA-specific guanine nucleotide exchange factor Syx is required for the polarity of actively migrating brain and breast tumor cells. This function of Syx is mediated by the selective activation of the RhoA downstream effector Dia1, the subsequent reorganization of microtubules, and the downregulation of focal adhesions and actin stress fibers. The data argue that directed cell migration requires the precise spatiotemporal regulation of Dia1 and ROCK activities in the cell. The recruitment of Syx to the cell membrane and the subsequent selective activation of Dia1 signaling, coupled with the suppression of ROCK and activation of cofilin-mediated actin reorganization, plays a key role in establishing cell polarity during directed cell migration.

I’m coming to GEF you: Regulation of RhoGEFs during cell migration

“…94 The loss in polarity is accompanied by an increase in the number and size of FA and a redistribution of actin to stress fibers and peripheral actin bundles. 93 The increase in stress fibers is unexpected when a RhoA-GEF is knocked down, and could reflect compensation by other RhoGEFs, as has been previously shown in other cases. For example, RhoA activity levels remain stable when p114Rho-GEF is depleted, due to a compensatory activation of GEF-H1.…”

“…When Syx1 expression is silenced in breast cancer cells, cells lose their elongated morphology and display a rounded flattened shape. 93 In a wound healing assay, Syx1 KD cells fail to form lamellipodia in the direction of the wound and are also defective reorienting the Golgi complex in the direction of migration. Chemotactic migration in a transwell assay is also inhibited.…”

“…Chemotactic migration in a transwell assay is also inhibited. 93 Similarly, silencing Syx1 in vivo in zebrafish results in inhibition of migration of endothelial cells in intersegmental vessels. 94 The loss in polarity is accompanied by an increase in the number and size of FA and a redistribution of actin to stress fibers and peripheral actin bundles.…”

“…37 Both the ability to bind PDZ proteins and to activate RhoA are required for Syx function in the establishment of polarity, suggesting the localized activation of RhoA is essential. 93 Interestingly, the Syx gene expresses two isoforms by alternative splicing; the full-length Syx1, and an almost identical isoform, Syx2, which is just two amino acids shorter and is unable to interact with PDZ domains.…”

Establishment of epithelial polarity – GEF who's minding the GAP?

“…Syx-mediated RhoA activation promotes endothelial junction integrity and barrier function in vitro and in vivo, at least in part by regulating the levels of VE-cadherin at the plasma membrane (Ngok et al, 2012). The role of Syx in epithelial cell polarity is unclear; however, it plays an important role in the directed cell migration and front-rear polarization of migrating brain and breast tumor cells (Dachsel et al, 2013), as well as in oligodendrocyte progenitor cells (OPCs) along white matter tracks (Binamé et al, 2013). Importantly, in the latter case, Crumbs and Par polarity complexes are recruited by OPCs that express the proteoglycan NG2 (also known as CSPG4), resulting in RhoA-to-Rac1 signaling through Tiam1 (Binamé et al, 2013).…”