Tyrosine 251 at the C‐terminus of neuronal glycoprotein M6a is critical for neurite outgrowth

Abstract

Neuronal glycoprotein M6a is involved in neuronal plasticity, promoting neurite and filopodia outgrowth and, likely, synaptogenesis. Polymorphisms in the human M6a gene GPM6A have recently been associated with mental illnesses such as schizophrenia, bipolar disorders, and claustrophobia. Nevertheless, the molecular bases underlying these observations remain unknown. We have previously documented that, to induce filopodia formation, M6a depends on the association of membrane lipid microdomains and the activation of Src and mitogen-activated protein kinase kinases. Here, in silico analysis of the phosphorylation of tyrosine 251 (Y251) at the C-terminus of M6a showed that it could be a target of Src kinases. We examined whether phosphorylation of M6a at Y251 affects neurite and filopodia outgrowth and the targets involved in its signal propagation. This work provides evidence that the Src kinase family and the phosphatidylinositide 3-kinase (PI3K), but not Ras, participate in M6a signal cascade leading to neurite/filopodia outgrowth in hippocampal neurons and murine neuroblastoma N2a cells. Phosphorylation of M6a at Y251 is essential only for neurite outgrowth by the PI3K/AKT-mediated pathway and, moreover, rescues the inhibition caused by selective Src inhibitor and external M6a monoclonal antibody treatment. Thus, we suggest that phosphorylation of M6a at Y251 is critical for a specific stage of neuronal development and triggers redundant signaling pathways leading to neurite extension.

Filopodia formation driven by membrane glycoprotein M6a depends on the interaction of its transmembrane domains

“…We also found that M6a colocalizes with the lipid raft resident family of Src kinases in different cell types and that M6a phosphorylated at Y251 induces neuritogenesis by recruitment and activation of Src and Akt kinases to the cell surface (Formoso et al . ).…”

“…; Formoso et al . ). In support of this hypothesis, in this work, we established the functional role of certain residues in M6a TMDs, which were seen to influence both self‐interaction and stability.…”

“…Dissociated neuronal cultures were prepared from rat hippocampi of embryonic day 19, as previously described (Formoso et al . ). Briefly, tissues were treated with 0.25% trypsin in Hanks' solution at 37°C for 15 min.…”

“…; Formoso et al . ). In mice and treeshrews, we identified Gpm6a as a chronic stress‐regulated gene (Alfonso et al .…”

“…M6a, together with M6b, proteolipid protein (PLP) and DM20, belongs to the PLP family, and has been related to neuronal plasticity in different experimental models (Lagenaur et al 1992;Alfonso et al 2005;Michibata et al 2009;Huang et al 2011;Sato et al 2011a;Zappia et al 2012). M6a positively contributes to neuritogenesis, filopodia outgrowth and synapse formation in M6a-over-expressing neurons, but its mechanism of action remains unknown (Alfonso et al 2005;Fuchsova et al 2009;Formoso et al 2015). In mice and treeshrews, we identified Gpm6a as a chronic stress-regulated gene (Alfonso et al 2006).…”