The Scaffold Protein POSH Regulates Axon Outgrowth

Abstract

How scaffold proteins integrate signaling pathways with cytoskeletal components to drive axon outgrowth is not well understood. We report here that the multidomain scaffold protein Plenty of SH3s (POSH) regulates axon outgrowth. Reduction of POSH function by RNA interference (RNAi) enhances axon outgrowth in differentiating mouse primary cortical neurons and in neurons derived from mouse P19 cells, suggesting POSH negatively regulates axon outgrowth. Complementation analysis reveals a requirement for the third Src homology (SH) 3 domain of POSH, and we find that the actomyosin regulatory protein Shroom3 interacts with this domain of POSH. Inhibition of Shroom3 expression by RNAi leads to increased process lengths, as observed for POSH RNAi, suggesting that POSH and Shroom function together to inhibit process outgrowth. Complementation analysis and interference of protein function by dominant-negative approaches suggest that Shroom3 recruits Rho kinase to inhibit process outgrowth. Furthermore, inhibition of myosin II function reverses the POSH or Shroom3 RNAi phenotype, indicating a role for myosin II regulation as a target of the POSH-Shroom complex. Collectively, these results suggest that the molecular scaffold protein POSH assembles an inhibitory complex that links to the actin-myosin network to regulate neuronal process outgrowth.

Activation of LILRB2 signal pathway in temporal lobe epilepsy patients and in a pilocarpine induced epilepsy model

“…Recent studies confirmed that the scaffold proteins of SH3s (POSH), actin-myosin regulatory protein SHROOM3, and Rho Kinase (ROCK) have been involved in the downstream signaling pathways of PirB to participate in the inhibition of neuronal outgrowth (Dickson et al, 2010;Taylor et al, 2008). The important downstream molecules in the PirB pathway were also observed in the present study.…”

“…Experiments in vitro indicate that MAG restricts axon growth by binding to PirB, and this process is accompanied by the activation of SHP1/ 2 (Fujita et al, 2011). Moreover, in the cortical neurons, downregulation of PirB expression using RNA interference led to increased outgrowth of processes (Taylor et al, 2008). To our knowledge, axonal sprouting has been documented in the hippocampal formation, amygdala and temporal cortices in epileptic human and animal brains (Tolner et al, 2003;Yan et al, 2012).…”

“…In vitro, down regulation of POSH expression by RNAi leads to increased process lengths, as observed for SHROOM3 RNAi, suggesting that POSH and SHROOM3 function together to inhibit neurite outgrowth (Taylor et al, 2008). Furthermore, the role of POSH in the regulation of synaptic growth has been proven in a drosophila model of frontotemporal dementia (West et al, 2015).…”

Pax6-dependent Shroom3 expression regulates apical constriction during lens placode invagination

“…Shroom3 is a multi-domain protein that can interact with and/or recruit components of the cytoskeletal machinery, including actin and Rho kinase (Rock1/2) (Hildebrand and Soriano, 1999;Nishimura and Takeichi, 2008;Taylor et al, 2008). Shroom3 also possesses a proline-rich sequence (FPn) that matches the consensus binding sequence of the Mena/Vasp family of proteins and raises the possibility that there might be an interaction between the FPn-binding (EVH1) domain of Mena/Vasp and Shroom3 (Fig.…”

Cell dynamics in fetal intestinal epithelium: implications for intestinal growth and morphogenesis

“…It has been shown that AB elongation of pseudostratified epithelial cells in the developing neural tube depends on Shroom3, a PDZ binding domaincontaining protein that localizes to the apical adherens junction (Haigo et al, 2003;Hildebrand, 2005;Hildebrand and Soriano, 1999). Interestingly, Shroom3 also controls apical constriction, another attribute shared by most pseudostratified epithelia (Haigo et al, 2003;Hildebrand, 2005;Lee et al, 2009;Lee et al, 2007;Nishimura and Takeichi, 2008;Taylor et al, 2008).…”