Protein kinase C phosphorylation of a {gamma}-Protocadherin C-terminal lipid-binding domain regulates focal adhesion kinase inhibition and dendrite arborization [Cell Biology]

July 2nd, 2015 by Keeler, A. B., Schreiner, D., Weiner, J. A.

The γ-Protocadherins (γ-Pcdhs) are a family of 22 adhesion molecules with multiple critical developmental functions, including the proper formation of dendritic arbors by forebrain neurons. The γ-Pcdhs bind to, and inhibit, focal adhesion kinase (FAK) via a constant C-terminal cytoplasmic domain shared by all 22 proteins. In cortical neurons lacking the γ-Pcdhs, aberrantly high activity of FAK and of PKC disrupts dendrite arborization. Little is known, however, about how γ-Pcdh function is regulated by other factors. Here we show that PKC phosphorylates a serine residue situated within a phospholipid-binding motif at the shared γ-Pcdh C-terminus. Western blots using a novel phospho-specific antibody against this site suggest that a portion of γ-Pcdh proteins is phosphorylated in the cortex in vivo. We find that PKC phosphorylation disrupts both phospholipid binding and γ-Pcdh inhibition of (but not binding to) FAK. Introduction of a non-phosphorylatable (S/A) γ-Pcdh construct into wild-type cortical neurons significantly increases dendrite arborization. This same S/A construct can also rescue dendrite arborization defects in γ-Pcdh null neurons cell autonomously. Consistent with these data, introduction of a phosphomimetic (S/D) γ-Pcdh construct, or treatment with a PKC activator, reduces dendrite arborization in wild-type cortical neurons. Together, these data identify a novel mechanism through which γ-Pcdh control of a signaling pathway important for dendrite arborization is regulated.
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