Src-mediated phosphorylation of beta Pix-b regulates dendritic spine morphogenesis

Abstract

PAK-interacting guanine nucleotide exchange factor (beta Pix; also known as Arhgef7) has been implicated in many actin-based cellular processes, including spine morphogenesis in neurons. However, the molecular mechanisms by which beta Pix controls spine morphology remain elusive. Previously, we have reported the expression of several alternative spliced beta Pix isoforms in the brain. Here, we report a novel finding that the b isoform of beta Pix (beta Pix-b) mediates the regulation of spine and synapse formation. We found that beta Pix-b, which is mainly expressed in neurons, enhances spine and synapse formation through preferential localization at spines. In neurons, glutamate treatment efficiently stimulates Rac1 GEF activity of beta Pix-b. The glutamate stimulation also promotes Src-mediated phosphorylation of beta Pix-b in both an AMPA receptor- and NMDA receptor-dependent manner. Tyrosine 598 (Y598) of beta Pix-b is identified as the major Src-mediated phosphorylation site. Finally, Y598 phosphorylation of beta Pix-b enhances its Rac1 GEF activity that is critical for spine and synapse formation. In conclusion, we provide a novel mechanism by which beta Pix-b regulates activity-dependent spinogenesis and synaptogenesis via Src-mediated phosphorylation.