Abstract 3600: HspA12B Promotes Angiogenesis through Suppressing AKAP12 and Up-Regulating VEGF Pathway

We have previously shown that HspA12B, a member of HspA70 family subfamily 12, is a novel angiogenesis regulator that is preferentially expressed in endothelial cells (ECs) and required for angiogenesis in vitro . The mechanism by which HspA12B regulates angiogenesis, however, is unknown. In this study we identified AKAP12/SSeCKS as a HSPA12B-interacting protein through a yeast two-hybrid screening and confirmed the interaction by co-immunoprecipitation and co-localization. We observed that HspA12B negatively regulated the expression of AKAP12/SSeCKS, a cancer metastasis repressor that inhibits VEGF expression and angiogen-esis. In HUVEC, HspA12B knockdown increased AKAP12 levels, decreased VEGF by more than 75%, and down-regulated Akt and pAkt; whereas HspA12B over expression decreased AKAP12 and more than doubled VEGF levels. We further identified a 32-AA domain in AKAP12 that was capable of interacting with HspA12B. Overexpression of this 32-AA domain in HUVEC disrupted the HspA12B-AKAP12 interaction and decreased VEGF expression by more than 70%, suggesting the importance of HspA12B-AKAP12 interaction in regulating VEGF. We also observed that HspA12B expression was increased more than 2 folds in ECs by hypoxia or shearing stress, and induced in ischemic rat heart. Inhibition of HspA12B abolished hypoxia-induced tubule formation. Adeno-HspA12B promoted angiogenesis in DIVAA assay. We concluded that this is the first evidence that HspA12B promotes angiogenesis through regulating VEGF by way of suppressing AKAP12. Our finding is the first example of an EC-specific molecular chaperone acting as the regulator of angiogenesis.