Dual role of Fyn in the regulation of FAK(+)6,7 by cannabinoids in hippocampus

In hippocampus endocannabinoids modulate synaptic function and plasticity a nd increase tyrosine phosphorylation of several proteins, including focal a dhesion kinase (FAK). Autophosphorylation of FAK on Tyr-397 is generally a critical step for its activation, allowing the recruitment of Src family ki nases, and phosphorylation of FAK and associated proteins. We have examined the mechanisms of the regulation of FAK by cannabinoids in rat and mouse h ippocampal slices. Anandamide and 2-arachidonoylglycerol, two endocannabino ids, and Delta9-tetrahydrocannabinol, stimulated tyrosine phosphorylation o f FAK(+)6,7, a neuronal splice isoform of FAK, on several residues includin g Tyr-397. Cannabinoids increased phosphorylation of p130-Cas, a protein as sociated with FAK, but had no effect on PYK2, a tyrosine kinase related to FAK and enriched in hippocampus. Pharmacological experiments and the use of knockout mice demonstrated that the effects of cannabinoids were mediated through CB1 receptors. These effects were sensitive to manipulation of cAMP -dependent protein kinase, suggesting that they were mediated by inhibition of a cAMP pathway. PP2, an Sre family kinase inhibitor, prevented the effe cts of cannabinoids on p130-Cas and on FAK(+)6,7 tyrosines 577 and 925, but not 397, indicating that FAK autophosphorylation was upstream of Src famil y kinases in response to CB1-R stimulation. Endocannabinoids increased the association of Fyn, but not Sre, with FAK(+)6,7. In hippocampal slices from Fyn -/- mice, the levels of p130-Cas were increased, and the effects of en docannabinoids on tyrosine phosphorylation, including of Tyr-397, were comp letely abolished. These results demonstrate the specific functional associa tion of Fyn with FAK(+)6,7 in a pathway regulated by endocannabinoids, in w hich Fyn may play roles dependent and independent of its catalytic activity .