Our objectives were to determine whether heme oxygenase-1 is a second messenger for prolactin-mediated angiogenesis. Endothelial cell proliferation and angiogenesis assay demonstrated that cell number and capillary formation were increased by prolactin (10 and 25 ng/ml). Both protein synthesis and mRNA analysis confirmed that HO-1 expression was induced by prolactin in cultured endothelial cells and occurred in a concentration-dependent manner. Endothelial cells transduced with retrovirus-mediated delivery of HO-1 gene in sense and antisense orientation were used to further determine whether HO-1 overexpression or underexpression modulated prolactin-mediated endothelial cell proliferation and angiogenesis. Incubation of human microvessel endothelial cells transduced with HO-1 in sense orientation resulted in enhancement of prolactin-mediated increase in endothelial cell proliferation and angiogenesis, whereas inhibition of HO-1 by transduction of HO-1 in antisense orientation prevented prolactin increase in endothelial cell proliferation. Similarly, addition of stannic mesoporphyrin, the inhibitor of HO activity, prevented PRL-mediated increase in endothelial cell proliferation. Our results demonstrated for the first time, that prolactin-mediated angiogenesis and cell proliferation was dependent on HO-1 gene expression.

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