FAK and Pyk2: Paralogous Kinases with Opposing Roles in Vasculogenic Mimicry in Triple-Negative Breast Cancer.

Vasculogenic mimicry (VM) is a non-endothelial mode of tumor vascularization in which aggressive cancer cells form vessel-like networks that support microcirculation, metastasis, and resistance to anti-angiogenic therapies. VM is particularly prominent in triple-negative breast cancer (TNBC), but its molecular regulators remain incompletely understood. Focal adhesion kinase (FAK) and its paralog, proline-rich tyrosine kinase 2 (Pyk2), are closely related non-receptor tyrosine kinases implicated in epithelial-to-mesenchymal transition (EMT), invasion, and metastasis in TNBC. However, their roles in VM have not been defined. Here we perform transcriptomic analysis of FAK and Pyk2 clinical expression patterns using TNMplot V2, DepMap, and patient cohort datasets to systematically dissect the distinct contributions of FAK and Pyk2 to VM in TNBC. Our in vitro tube formation assay shows that in TNBC cells, knockdown of FAK, but not Pyk2, results in failure to form robust 3D vessel-like networks in Matrigel. Similarly, overexpression of Pyk2, but not FAK, in TNBC cells results in poor vessel-like network formation. Consistent with these findings, analysis of two independent patient cohorts (TCGA-BRCA and METABRIC) revealed selective upregulation of FAK in TNBC, while Pyk2 was inversely associated with vasculogenic-mimicry-associated gene expression, supporting the opposing roles of the two kinases in patient tumors. Taken together, these findings establish that FAK and Pyk2 govern VM through non-redundant, kinase-specific, and functionally opposed mechanisms: FAK acting as a positive regulator of VM, and Pyk2 as a context dependent suppressor of VM at elevated levels. These results nominate FAK as a candidate target for suppressing VM-driven tumor perfusion in TNBC and suggest that dual FAK/Pyk2 inhibition warrants caution hypotheses that remain to be tested pharmacologically.