Mapping endothelial functional phenotype in cancer by unveiling the kinase and phosphatase drivers

Endothelial cells (EC) are state-dependent regulators of the tumor ecosystem: quiescent ECs promote homeostasis; proliferative ECs stimulate tumor growth. Tumors, in turn, promote pro-tumorigenic EC phenotype. We studied functional and phosphorylative transformations on EC state in cancer. Quiescent HUVECs cultured in breast cancer cell-conditioned media displayed marked elongation and impaired wound healing. Quantitative mass spectrometry identified phosphorylative regulators of this dysfunctional transformation. Growth factor receptor kinases showed decreased, rather than increased activity, suggesting that EC regulation in tumors can arise other than from classic growth-factor-mediated angiogenesis alone. Of the 152 kinases and phosphatases across 62 families, six were chosen for functional validation using pharmacologic inhibitors. Inhibiting Akt and Ptp1b restored EC regulatory state, warranting further investigation as therapeutic targets; Src inhibition, however, promoted the dysfunctional phenotype, suggesting caution for Src inhibitors as EC-regulating therapies. Mapping phosphorylative drivers reveals complex relationships between EC phenotype, transformation, and regulation, and may shed light on how existing cancer-targeting inhibitors affect tumor endothelium. Data are available via ProteomeXchange with identifier PXD020333.