αB-crystallin a effector of unfolded protein response confers anti-VEGF resistance to breast cancer via maintenance of intracrine VEGF in endothelial cells

摘要

Effective inhibition of angiogenesis targeting the tumor endothelial cells requires identification of key cellular and molecular mechanisms associated with survival of vasculatures within the tumor microenvironment. Intracellular autocrine (intracrine) VEGF production by endothelial cells plays a critical role on the vasculature homeostasis. In vitro breast cancer cell-stimulated activation of the unfolded protein response (UPR) of the endothelial cells contributes to maintenance of the intracrine VEGF levels in the endothelial cells through the up-regulation of a previous un-described downstream effector- αB-crystallin (CRYAB). Short interfering RNA-mediated knockdown of two major UPR proteins-IRE1 and ATF6, led to attenuated CRYAB expression of the endothelial cells. Finally, inhibition of CRYAB blocked the breast cancer cell-stimulated increase in the endogenous VEGF levels of the endothelial cells. A VEGF limited proteolysis assay further revealed that CRYAB protected VEGF for proteolytic degradation. Here we report that the molecular chaperone-CRYAB) was significantly increased and co-localized with tumor vessels in a breast cancer xenograft. Specifically, neutralization of VEGF induced higher levels of CRYAB expression in the endothelial cells co-cultured with MDA-MB-231 or the breast cancer xenograft with a significant survival benefit. However, knockdown of CRYAB had a greater inhibitory effect on endothelial survival. These findings underscore the importance of defining a role for intracrine VEGF signaling in sustaining aberrant tumor angiogenesis and strongly implicate UPR/CRYAB as dichotomous parts of a crucial regulation pathway for maintaining intracrine VEGF signaling.