Inducible FAK Deletion but not FAK Inhibition in Endothelial Cells Activates p53 to Suppress Tumor Growth in PYK2-null Mice

Focal adhesion kinase (FAK) functions as a signaling and scaffolding protein within endothelial cells (ECs) impacting blood vessel function and tumor growth. Interpretations of EC FAK-null phenotypes are complicated by related PYK2 (protein tyrosine kinase 2) expression, and to test this, we created PYK2-/- FAKfl/fl mice with tamoxifen-inducible EC-specific Cre recombinase expression. At 11 weeks of age, EC FAK inactivation resulted in increased heart and lung mass and vascular leakage only on a PYK2-/- background. Surprisingly, [~]90% of PYK2-/- EC FAK-/- mice survived to 75 weeks of age. Syngeneic melanoma, breast, or lung carcinoma tumors did not grow in PYK2-/- EC FAK-/- mice, but tumors grew normally in PYK2-/- EC FAKfl/fl mice lacking Cre. This tumor inhibitory phenotype was associated with abortive EC vessel sprouting, enhanced EC p53 tumor suppressor and p21CIP1 (cyclin-dependent inhibitor 1) expression, and alterations in serum cytokine levels. To discern the role of FAK kinase versus scaffolding activity in ECs, we generated kinase defective (FAK K454R, KD) PYK2-/- EC FAKfl/KD and PYK2-/- EC FAKfl/WT (WT, wildtype) mice. Hemizygous EC FAK-/KD expression supported primary tumor growth but not metastasis, implicating EC FAK activity in tumor dissemination. In vitro, hemizygous expression of either WT or KD FAK suppressed EC p21CIP1 levels and cell death observed in primary PYK2-/- EC FAK-/- ECs. Combined FAK and PYK2 knockdown in tumor cells also increased p21CIP1 and PARP1 (poly ADP-ribose polymerase 1) levels in a p53-associated manner impacting anchorage-independent growth. Together, these results underscore the linkage between PYK2 and FAK loss with p53 activation impacting tumor growth. Impact StatementPYK2-null combined with endothelial cell-specific FAK transgenic mouse models show that loss of FAK activity limits tumor spread and that genetic or chemical degradation preventing combined FAK-PYK2 expression may be an approach to induce a p53-associated anti-tumor response.