Caveolae compartmentalization of heme oxygenase‐1 in endothelial cells

Abstract

The heme oxygenase (HO) and nitric oxide synthase (NOS) enzymes generate the gaseous signaling molecules carbon monoxide (CO) and nitric oxide, respectively. Constitutive NOSs localize to caveolae, and their activities are modulated by caveo‐ lin‐1. Nothing is known of the localization of the inducible heme oxygenase‐1 (HO‐1) in plasma mem‐ brane caveolae. Thus, we examined the distribution and subcellular localization of HO‐1, biliverdin reduc‐ tase (BVR), and NADPH:cytochrome P450 reductase (NPR) in pulmonary artery endothelial cells. Each of these proteins localized in part to plasma membrane caveolae in endothelial cells. Inducers of HO‐1 or overexpression of HO‐1 increased the content of this protein in a detergent‐resistant fraction containing caveolin‐1. Inducible HO activity appeared in plasma membrane, cytosol, and isolated caveolae. In addition, caveolae contained endogenous BVR activity, supporting the same compartmentalization of both enzymes. Caveolin‐1 physically interacted with HO‐1, as shown by coimmunoprecipitation studies. HO activity dramati‐ cally increased in cells expressing caveolin‐1 antisense transcripts, suggesting a negative regulatory role for caveolin‐1. Conversely, caveolin‐1 expression attenu‐ ated LPS‐inducible HO activity. Since their initial char‐ acterization in 1969, HO enzymes have been described as endoplasmic reticulum‐associated proteins. We dem‐ onstrate for the first time the localization of heme degradation enzymes to plasma membrane caveolae, and present novel evidence that caveolin‐1 interacts with and modulates HO activity.—Kim, H. P., Wang, X., Galbiati, F., Ryter, S. W., Choi, A. M. K. Caveolae compartmentalization of heme oxygenase‐1 in endothe‐ lial cells. FASEB J. 18, 1080–1089 (2004)