Signal transduction pathway regulating prostaglandin EP3 receptor-induced neurite retraction: requirement for two different tyrosine kinases

We reported previously that activation of the prostaglandin E receptor EP3 subtype triggered neurite retraction through the small GTPase Rho-, and its target, RhoA-binding kinase alpha. (ROKx)-, dependent pathway in EP3 receptor-expressing PC12 cells. Here we examined the involvement of tyrosine kinases in this pathway in nerve growth factor-differentiate PC12 cells. Tyrphostin; A25, a tyrosine kinase inhibitor, blocked neurite retraction and cell rounding induced by activation of the EP3 receptor, however, it failed to block neurite retraction and cell rounding induced by microinjection of constitutively active RhoA, RhoA(v14), indicating that a tyrphostin-sensitive tyrosine kinase was involved in the pathway from the EP3 receptor to Rho activation. On the other hand, genistein, another tyrosine kinase inhibitor, blocked neurite retraction and cell rounding induced by both activation of the EP3 receptor and microinjection of RhoA(v14). However, genistein did not block neuronal morphological changes induced by microinjection of a constitutively active mutant of ROK alpha. These results indicate that two different tyrosine kinases, tyrphostin A25-sensitive and genistein-sensitive kinases, are involved in the EP3 receptor-mediated neurite retraction acting upstream and downstream of Rho, respectively.