Beta1PIX, the PAK-interacting exchange factor, requires localization via a coiled-coil region to promote microvillus-like structures and membrane ruffles
ABSTRACT PIX is a Rho-family guanine nucleotide exchange factor that binds PAK. We previously described two isoforms of PIX that differ in their N termini. Here, we report the identification of a new splice variant of betaPIX, designated beta2PIX, that is the dominant species in brain and that lacks the region of approximately 120 residues with predicted coiled-coil structure at the C terminus of beta1PIX. Instead, beta2PIX contains a serine-rich C terminus. To determine whether these splice variants differ in their cellular function, we studied the effect of expressing these proteins in HeLa cells. We found that the coiled-coil region plays a key role in the localization of beta1PIX to the cell periphery and is also responsible for PIX dimerization. Overexpression of beta1, but not beta2PIX, drives formation of membrane ruffles and microvillus-like structures (via activation of Rac1 and Cdc42, respectively), indicating that its function requires localized activation of these GTPases. Thus, beta1PIX, like other RhoGEFs, exerts specific morphological functions that are dependent on its intracellular location and are mediated by its C-terminal dimerization domain.
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- "Besides the cc-domain, the pleckstrin homology (PH) domain of PIX proteins has also been reported to play a role in intracellular targeting. As the PH domain of aPIX and bPIX share only 72% amino acid homology (Koh et al., 2001), they might be directed to different target sites within the same cell. Importantly, aPIX and bPIX may also form heterodimers via their cc-domains (Rosenberger et al., 2003). "
ABSTRACT: In the cerebral cortex of reeler mutant mice lacking reelin expression, neurons are malpositioned and display misoriented apical dendrites. Neuronal migration defects in reeler have been studied in great detail, but how misorientation of apical dendrites is related to reelin deficiency is poorly understood. In wild-type mice, the Golgi apparatus transiently translocates into the developing apical dendrite of radially migrating neurons. This dendritic Golgi translocation has recently been shown to be promoted by reelin. However, the underlying signalling mechanisms are largely unknown. Here, we show that the Cdc42/Rac1 guanine nucleotide exchange factor αPIX/Arhgef6 promoted translocation of Golgi cisternae into developing dendrites of hippocampal neurons. Reelin treatment further increased the αPIX-dependent effect. In turn, overexpression of exchange activity-deficient αPIX or dominant-negative (dn) Cdc42 or dn-Rac1 impaired dendritic Golgi positioning, an effect that was not compensated by reelin treatment. Together, these data suggest that αPIX may promote dendritic Golgi translocation, as a downstream component of a reelin-modulated signalling pathway. Finally, we found that reelin promoted the translocation of the Golgi apparatus into the dendrite that was most proximal to the reelin source. The distribution of reelin may thus contribute to the selection of the process that becomes the apical dendrite.European Journal of Neuroscience 02/2013; 37(9). DOI:10.1111/ejn.12153 · 3.67 Impact Factor
Frontiers in Physiology 07/2012; 3:268. DOI:10.3389/fphys.2012.00268 · 3.50 Impact Factor
- "Further, Bagrodia et al. (1998) identified βPix (named p85Cool-1) and a smaller alterative splice variant (p50Cool-1) as two proteins that facilitated interactions between PAK and DBL homology (DH) and pleckstrin homology (PH) domains. Finally, Koh et al. (2001) reported an isoform of βPix designated β 2 Pix; that isoform contained a serine-rich region not found in the original βPix protein (which is now designated as β 1 Pix-a, Kim et al., 2000) nor the β 1 Pix-b and β 1 Pix-c isoforms (Oh et al., 1997; Kim et al., 2000). The structure and functional domains of β 1 Pix are provided in Figure 1. "
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- "β-PIX is a multidomain protein comprised of an SH3 domain, a DH-PH Rac/Cdc42 GEF domain, a GIT1-binding region, and a proline-rich region (Fig. 3) (Rosenberger and Kutsche, 2006). In the brain, two major β-PIX isoforms are expressed that differ only at their C-termini; β1-PIX possesses a coiled-coil dimerization domain and a PDZ-binding motif, whereas β2-PIX contains a serine-rich region (Koh et al., 2001). These two β-PIX isoforms are present at high levels during development, and they continue to be expressed in the adult in restricted brain regions such as the hippocampus and cerebellum (Kim et al., 2000). "
ABSTRACT: Synapses are specialized cell-cell contacts that mediate communication between neurons. Most excitatory synapses in the brain are housed on dendritic spines, small actin-rich protrusions extending from dendrites. During development and in response to environmental stimuli, spines undergo marked changes in shape and number thought to underlie processes like learning and memory. Improper spine development, in contrast, likely impedes information processing in the brain, since spine abnormalities are associated with numerous brain disorders. Elucidating the mechanisms that regulate the formation and plasticity of spines and their resident synapses is therefore crucial to our understanding of cognition and disease. Rho-family GTPases, key regulators of the actin cytoskeleton, play essential roles in orchestrating the development and remodeling of spines and synapses. Precise spatio-temporal regulation of Rho GTPase activity is critical for their function, since aberrant Rho GTPase signaling can cause spine and synapse defects as well as cognitive impairments. Rho GTPases are activated by guanine nucleotide exchange factors (GEFs) and inhibited by GTPase-activating proteins (GAPs). We propose that Rho-family GEFs and GAPs provide the spatiotemporal regulation and signaling specificity necessary for proper Rho GTPase function based on the following features they possess: (i) existence of multiple GEFs and GAPs per Rho GTPase, (ii) developmentally regulated expression, (iii) discrete localization, (iv) ability to bind to and organize specific signaling networks, and (v) tightly regulated activity, perhaps involving GEF/GAP interactions. Recent studies describe several Rho-family GEFs and GAPs that uniquely contribute to spinogenesis and synaptogenesis. Here, we highlight several of these proteins and discuss how they occupy distinct biochemical niches critical for synaptic development.Progress in Neurobiology 07/2011; 94(2):133-48. DOI:10.1016/j.pneurobio.2011.04.011 · 10.30 Impact Factor