Pyk2 and FAK differentially regulate progression of the cell cycle

We have previously identified FAK and its associated signaling pathways as a mediator of cell cycle progression by integrins. In this report, me have analyzed the potential role and mechanism of Pyk2, a tyrosine kinase closel y related to FAK, in cell cycle regulation by using tetracycline-regulated expression system as well as chimeric molecules. We have found that inducti on of Pyk2 inhibited G(1) to S phase transition whereas comparable inductio n of FAK expression accelerated it, Furthermore, expression of a chimeric p rotein containing Pyk2 N-terminal and kinase domain and FAK C-terminal doma in (PFhy1) increased cell cycle progression as FAK, Conversely, the complem entary chimeric molecule containing FAK N-terminal and kinase domain and Py k2 C-terminal domain (FPhy2) inhibited cell cycle progression to an even gr eater extent than Pyk2. Biochemical analyses indicated that Pyk2 and FPhy2 stimulated JNK activation whereas FAK or PFhy1 had little effect on it, sug gesting that differential activation of JNK by Pyk2 may contribute to its i nhibition of cell cycle progression, In addition, Pyk2 and FPhy2 to a great er extent also inhibited Erk activation in cell adhesion whereas FAK and PF hy1 stimulated it, suggesting a role for Erk activation in mediating differ ential regulation of cell cycle by Pyk2 and FAK. A role for Erk and JNK pat hways in mediating the cell cycle regulation by FAK and Pyk2 was also confi rmed by using chemical inhibitors for these pathways, Finally, we showed th at while FAK and PFhy1 were present in focal contacts, Pyk2 and FPhy2 were localized in the cytoplasm, Interestingly, both Pyk2 and FPhy2 (to a greate r extent) were tyrosine phosphorylated and associated with Src and Fyn, Thi s suggested that they may inhibit Erk activation in an analogous manner as the mislocalized FAK mutant Delta C14 described previously by competing wit h endogenous FAK for binding signaling molecules such as Src and Fyn. This model is further supported by an inhibition of endogenous FAK association w ith active Src by Pyk2 and FPhy2 and a partial rescue by FAK of Pyk2-mediat ed cell cycle inhibition.