Neuronal ELAV proteins enhance mRNA stability by a PKCalpha-dependent pathway

More than 1 in 20 human genes bear in the mRNA 3' UTR a specific motif called the adenine- and uridine-rich element (ARE), which posttranscriptionally determines its expression in response to cell environmental signals. ELAV (embryonic lethal abnormal vision) proteins are the only known ARE-binding factors that are able to stabilize the bound mRNAs, thereby positively controlling gene expression. Here, we show that in human neuroblastoma SH-SY5Y cells, neuron-specific ELAV (nELAV) proteins (HuB, HuC, and HuD) are up-regulated and redistributed by 15 min of treatment with the activators of PKC phorbol esters and bryostatin-1. PKC stimulation also induces nELAV proteins to colocalize with the translocated PKCalpha isozyme preferentially on the cytoskeleton, with a concomitant increase of nELAV threonine phosphorylation. The same treatment promotes stabilization of growth-associated protein 43 (GAP-43) mRNA, a well known nELAV target, and induces an early increase in GAP-43 protein concentration, again only in the cytoskeletal cell fraction. Genetic or pharmacological inactivation of PKCalpha abolishes nELAV protein cytoskeletal up-regulation, GAP-43 mRNA stabilization, and GAP-43 protein increase, demonstrating the primary role of this specific PKC isozyme in the cascade of nELAV recruitment. Finally, in vivo PKC activation is associated with an up-regulation of nELAV proteins in the hippocampal rat brain. These findings suggest a model for gene expression regulation by nELAV proteins through a PKCalpha-dependent pathway that is relevant for the cellular programs in which ARE-mediated control plays a pivotal role.