Dynamic regulation of Homer binding to group I mGluRs by Preso1 and converging kinase cascades

In rat sympathetic neurons from the superior cervical ganglia (SCG) expressing metabotropic glutamate receptors (mGluRs) 1 or 5, overexpression of scaffolding Homer proteins, which bind to a Homer ligand in their C-termini, cause receptor clustering and uncoupling from ion channel modulation. In the absence of recombinant Homer protein overexpression, uncoupling of mGluRs from voltage dependent channels can be induced by expression of Preso1, an adaptor of proline directed kinases that phosphorylates the Homer ligand and recruits binding of endogenous Homer proteins. Here we show that in SCG neurons expressing mGluR1 or 5 and the receptor tyrosine kinase TrkB, treatment with BDNF produces a similar uncoupling of the receptors from calcium channels. We investigated the pathways that mediate this uncoupling and compared it with uncoupling observed with Preso1 expression. Both BDNFand Preso1-induced uncoupling requires residues T1151 and S1154 in the mGluR1 Homer ligand (TPPSPF). Uncoupling via Preso1 but not BDNF was prevented by expression of a dominant negative Cdk5 suggesting endogenous Cdk5 mediates Preso1-dependent phosphorylation of mGluR. dnCDK5 did not block the BDNF effect but this was sensitive to inhibitors of the MEK-ERK kinase cascade. Interestingly, the BDNF pathway appeared to require native Preso1 binding to mGluR, as over-expression of the Preso1 FERM domain, which mediates the Preso1-mGluR interaction, prevented BDNF-induced uncoupling. These data suggest that BDNF-TrkB and CDK5 pathways converge at the level of mGluR to similarly induce Homer ligand phosphorylation, recruit Homer binding, and uncouple mGluRs from channel regulation. This article has not been copyedited and formatted. The final version may differ from this version. JPET Fast Forward. Published on February 8, 2017 as DOI: 10.1124/jpet.116.238394 at A PE T Jornals on Feruary 0, 2017 jpet.asjournals.org D ow nladed from