PYK2 Negatively Regulates the Hippo Pathway in TNBC by Stabilizing TAZ Protein

The tumor suppressor Hippo pathway negatively regulates the transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) to inhibit cell growth and control organ size, whereas activation of YAP and TAZ is implicated in tumorigenesis and cancer metastasis. Here, we report that the nonreceptor tyrosine kinase PYK2 positively regulates TAZ and YAP transcriptional activity in triple-negative breast cancer (TNBC). We found that inhibition of PYK2 expression or its kinase activity substantially affects the steady-state level of TAZ and markedly facilitates its proteasomal degradation. This effect was specific to PYK2 inhibition and was not obtained by inhibition of FAK. Destabilization of TAZ was associated with profound effect of PYK2 inhibition on cell growth at low-density concomitant with reduced expression of TAZ-target genes and induction of cell apoptosis. We further show that PYK2 enhances the tyrosine phosphorylation of both TAZ and LATS1/2 and concomitantly TAZ stability, and that PYK2 protein level correlates with the level of TAZ protein in primary breast tumors. Together these observations suggest that PYK2 is an important regulator of the Hippo pathway, and its tyrosine kinase activity has a striking effect on TAZ stabilization and activation in TNBC.