Regulation of adenomatous polyposis coli protein during growth factor mediated cell extension

NGF-induced neurite extension involves regulating the activity of the microtubule-binding protein Adenomatous polyposis coli (APC) to stabilize microtubules within the cell extension. This process requires inhibition of glycogen-synthase kinase 3-beta (GSK-3beta), which otherwise phosphorylates APC and decreases APC binding to microtubules. However, the phosphorylation state of APC during neurite extension has not been analyzed directly. We show that NGF-induced neurite extension of PC12 cells causes phosphorylation of APC by MAPK/ERK pathway, and that this pathway acts in parallel to GSK-3beta inhibition to promote APC localization to the tip of cell extensions. APC is phosphorylated in vitro by ERK2 in sites known to mediate microtubule and actin binding. While GSK-3beta inhibition has been shown to promote APC binding and stabilization of microtubules, ERK phosphorylation inhibits APC interactions with actin, but not with microtubules. These results identify a previously unknown regulatory pathway of APC during NGF-induced neurite extension, and indicate that GSK-3beta and ERK act in parallel to regulate APC-cytoskeleton interactions during the formation of cell extensions.