Compensatory role for Pyk2 during angiogenesis in adult mice lacking endothelial cell FAK

Abstract

Focal adhesion kinase (FAK) plays a critical role during vascular development because knockout of FAK in endothelial cells (ECs) is embryonic lethal. Surprisingly, tamoxifen-inducible conditional knockout of FAK in adult blood vessels (inducible EC–specific FAK knockout [i-EC-FAK-KO]) produces no vascular phenotype, and these animals are capable of developing a robust growth factor–induced angiogenic response. Although angiogenesis in wild-type mice is suppressed by pharmacological inhibition of FAK, i-EC-FAK-KO mice are refractory to this treatment, which suggests that adult i-EC-FAK-KO mice develop a compensatory mechanism to bypass the requirement for FAK. Indeed, expression of the FAK-related proline-rich tyrosine kinase 2 (Pyk2) is elevated and phosphorylated in i-EC-FAK-KO blood vessels. In cultured ECs, FAK knockdown leads to increased Pyk2 expression and, surprisingly, FAK kinase inhibition leads to increased Pyk2 phosphorylation. Pyk2 can functionally compensate for the loss of FAK because knockdown or pharmacological inhibition of Pyk2 disrupts angiogenesis in i-EC-FAK-KO mice. These studies reveal the adaptive capacity of ECs to switch to Pyk2-dependent signaling after deletion or kinase inhibition of FAK.

Compensatory Function of Pyk2 Protein in the Promotion of Focal Adhesion Kinase (FAK)-null Mammary Cancer Stem Cell Tumorigenicity and Metastatic Activity

“…Fig. 4A shows that PF-573,228 inhibited FAK activation but had no effect on Pyk2, and PF-562,271 abolished both FAK and Pyk2 phosphorylation in both MaCSCs from Ctrl-MT and MFCKO-MT mice, as observed previously in other cells (45,48,49). Treatments of MaCSCs from Ctrl-MT mice with PF-573,228 and PF-562,271 both inhibited their tumorsphere formation (Fig.…”

“…Interestingly, a number of previous studies suggested that Pyk2 could be up-regulated upon FAK deletion and compensate for FAK functions in these cells, providing strong support for their overlapping functions (36,45), although other studies did not detect such compensatory expression of Pyk2 in different cells (28,46,47). Our results here revealed a selective up-regulation of Pyk2 in MaCSCs and metastatic nodules after FAK deletion in MFCKO-MT mice.…”

“…Pyk2 and FAK are structurally related cytoplasmic tyrosine kinases, but there have been conflicting data on whether they can promote overlapping cellular functions or oppose each other's activities due to their distinct subcellular localizations in some cells (36,41,45). Interestingly, a number of previous studies suggested that Pyk2 could be up-regulated upon FAK deletion and compensate for FAK functions in these cells, providing strong support for their overlapping functions (36,45), although other studies did not detect such compensatory expression of Pyk2 in different cells (28,46,47).…”

“…Furthermore, although FAK is widely expressed in various tissues, Pyk2 is expressed mainly in the central nervous system and in cells derived from hematopoietic lineages. Interestingly, several reports showed that deletion of FAK can lead to increased expression of endogenous Pyk2 to compensate for FAK functions in embryonic fibroblasts and adult endothelial cells (36,45), although such compensatory increase of Pyk2 expression was not found upon FAK deletion in several other cells (28,46,47).…”

Nuclear FAK: a New Mode of Gene Regulation from Cellular Adhesions

“…FAK deletion causes upregulated p53 levels, and under this condition, a compensatory Pyk2 expression is often observed (Lim et al, 2008c;Weis et al, 2008). Pyk2 also localizes to the nucleus and promotes p53 turnover to enhance cell proliferation upon FAK deletion in FAK-/-p21-/-MEFs.…”