The adhesion signaling molecule p190 RhoGAP is required for morphogenetic processes in neural development

Abstract

Rho GTPases direct actin rearrangements in response to a variety of extracellular signals. P190 RhoGAP (GTPase activating protein) is a potent Rho regulator that mediates integrin-dependent adhesion signaling in cultured cells. We have determined that p190 RhoGAP is specifically expressed at high levels throughout the developing nervous system. Mice lacking functional p190 RhoGAP exhibit several defects in neural development that are reminiscent of those described in mice lacking certain mediators of neural cell adhesion. The defects reflect aberrant tissue morphogenesis and include abnormalities in forebrain hemisphere fusion, ventricle shape, optic cup formation, neural tube closure, and layering of the cerebral cortex. In cells of the neural tube floor plate of p190 RhoGAP mutant mice, polymerized actin accumulates excessively, suggesting a role for p190 RhoGAP in the regulation of +Rho-mediated actin assembly within the neuroepithelium. Significantly, several of the observed tissue fusion defects seen in the mutant mice are also found in mice lacking MARCKS, the major substrate of protein kinase C (PKC), and we have found that p190 RhoGAP is also a PKC substrate in vivo. Upon either direct activation of PKC or in response to integrin engagement, p190 RhoGAP is rapidly translocated to regions of membrane ruffling, where it colocalizes with polymerized actin. Together, these results suggest that upon activation of neural adhesion molecules, the action of PKC and p190 RhoGAP leads to a modulation of Rho GTPase activity to direct several actin-dependent morphogenetic processes required for normal neural development.

Regulation of the Substrate Preference of p190RhoGAP by Protein Kinase C-Mediated Phosphorylation of a Phospholipid Binding Site

“…A variety of cellular proteins contain polybasic regions embedded with serines and threonines, and phosphorylation of these amino acids, typically by PKC, has been found to reduce the electrostatic attraction of these regions for phospholipid membranes . We have previously demonstrated that p190A is phosphorylated by PKC both in vitro and in vivo in epithelial cells . Subsequently, we found that the PKC isoform α was the most efficient among the various PKC enzyme isoforms for phosphorylating both p190A and p190B proteins.…”

“…Antagonism of Rac and Rho activity has been demonstrated to be required for several vital biological functions such as neurite outgrowth or directed cell migration. p190GAPs seem to play a significant role in this process − . Recent findings demonstrated that activated Rac1 was able to recruit p190B to the plasma membrane and enhance its RhoGAP activity, and this cross-talk between Rac and Rho GTPases was required for control of cell shape by integrin signaling .…”

“…Recent findings demonstrated that activated Rac1 was able to recruit p190B to the plasma membrane and enhance its RhoGAP activity, and this cross-talk between Rac and Rho GTPases was required for control of cell shape by integrin signaling . This mechanism seems not to function with p190A although p190A was also shown to be translocated to the cell membrane upon physiological stimuli such as the fibronectin surface or by PKC-activating phorbol esters ,,, . The observations that tyrosine phosphorylation and complex formation with p120RasGAP or p120-catenin are required for translocation of p190A , suggest that p190A may become part of a larger protein complex at the plasma membrane.…”

“…The size and varied domain structure of p190A definitely allow multiple interactions with proteins and lipids at the same time. PKCα has also been suggested to play a role in regulation of the distribution of p190A; however, the mechanism has not been clarified ,, . PKCα may have multiple effects: translocation of p190A could be affected indirectly, by promoting its interaction with other proteins, whereas direct phosphorylation of p190A regulates the lipid binding of the PBR, hence the substrate preference of the protein.…”

Distinct spatiotemporal contribution of morphogenetic events and mechanical tissue coupling during Xenopus neural tube closure

“…Interestingly, although defects in both CE and AC result in NTDs, failure of CE is correlated with spinal NTDs whereas failure of AC is correlated with anterior NTDs ( Greene et al, 1998 ; Hildebrand and Soriano, 1999 ; Brouns et al, 2000 ; Wallingford et al, 2002 ; Haigo et al, 2003 ), suggesting that although these two morphogenetic processes are both indispensable for NTC they have discrete spatial and temporal contribution during neural tube morphogenesis. However, at present the precise spatiotemporal contribution of these processes towards NTC is not clear.…”