The Signaling Adaptor Gab1 Regulates Cell Polarity by Acting as a PAR Protein Scaffold

Abstract

Summary Cell polarity plays a key role in development and is disrupted in tumors, yet the molecules and mechanisms that regulate polarity remain poorly defined. We found that the scaffolding adaptor GAB1 interacts with two polarity proteins, PAR1 and PAR3. GAB1 binds PAR1 and enhances its kinase activity. GAB1 brings PAR1 and PAR3 into a transient complex, stimulating PAR3 phosphorylation by PAR1. GAB1 and PAR6 bind the PAR3 PDZ1 domain and thereby compete for PAR3 binding. Consequently, GAB1 depletion causes PAR3 hypo-phosphorylation and increases PAR3/PAR6 complex formation, resulting in accelerated and enhanced tight junction formation, increased trans-epithelial resistance and lateral domain shortening. Conversely, GAB1 over-expression, in a PAR1/PAR3-dependent manner, disrupts epithelial apical-basal polarity, promotes multi-lumen cyst formation, and enhances growth factor-induced epithelial cell scattering. Our results identify GAB1 as a novel negative regulator of epithelial cell polarity that functions as a scaffold for modulating PAR protein complexes on the lateral membrane.

Shp2 promotes metastasis of prostate cancer by attenuating the PAR3/PAR6/aPKC polarity protein complex and enhancing epithelial-to-mesenchymal transition

“…3 Previous studies suggested that Shp2 might indirectly contribute to the regulation of the PAR polarity protein complexes. 12,26 We tackled this unsettled question by coimmunoprecipitation assays using antibodies against Shp2 or PAR proteins. As shown in Figure 6a, a physical interaction between Shp2 and PAR3 was detected in 293T cells.…”

Molecular determinants of KA1 domain-mediated autoinhibition and phospholipid activation of MARK1 kinase

“…Moreover, like several of these domains, notably C2 and PH domains, KA1 domains may bind both membrane and protein targets [49] — just as protein or peptide targets have been suggested for PH domains [50] and C2 domains [51]; for example. Yang et al [49] reported that the KA1 domain of PAR1b/MARK2 and other human MARK family kinases interacts with Gab1 by binding to an ~100 amino acid stretch (aa 152–250) in its unstructured region — potentially linking receptor tyrosine kinase signaling to control of cell polarity. Indeed, this study suggests that Gab1 acts as a scaffold to facilitate phosphorylation of PAR3 and possibly other polarity-regulating proteins by MARK2 [49].…”

“…Yang et al [49] reported that the KA1 domain of PAR1b/MARK2 and other human MARK family kinases interacts with Gab1 by binding to an ~100 amino acid stretch (aa 152–250) in its unstructured region — potentially linking receptor tyrosine kinase signaling to control of cell polarity. Indeed, this study suggests that Gab1 acts as a scaffold to facilitate phosphorylation of PAR3 and possibly other polarity-regulating proteins by MARK2 [49]. Just as acidic vesicles can activate our ‘mini’ MARK1 in vitro , overexpression of the KA1-binding region of Gab1 appears to increase MARK2 activation in cells.…”

Scribble regulates an EMT–polarity pathway through modulation of MAPK-ERK signaling to mediate junction formation

“…Tight junctions are recognized to have important roles in acting as signaling platforms in a variety of cellular processes (Balda and Matter, 2008;Balda and Matter, 2009;Farkas et al, 2012;González-Mariscal et al, 2008;Steed et al, 2010;Yang et al, 2012). In turn, components of numerous intracellular signaling pathways including G-proteins, PLCc and PKC have been implicated in the regulation and maintenance of tight junction integrity (Nunbhakdi-Craig et al, 2002;Nusrat et al, 1995;Stuart and Nigam, 1995;Terry et al, 2011;Walsh et al, 2001;Ward et al, 2002).…”