AbstractWe developed a retrovirus‐mediated human heme oxygenase‐1 (HO‐1) gene expression system and assessed the impact of heme on the inducibility of the HO‐1 gene in rat lung microvessel (RLMV) endothelial cells and in newborn Sprague‐Dawley (SD) rats. Overexpression of the HO‐1 gene driven by HO‐1 promoter (HOP) resulted in an increase in HO‐1 protein and HO activity by 4.8‐ and 1.3‐fold, respectively, compared to the viral LTR promoter. The increased HO‐1 gene expression was associated with the enhancement of CO production. In cells transduced by HOP‐driven HO‐1 gene, there was a decrease in basal cyclooxygenase (COX) activity as measured by PGE2. The degree of HO‐1 expression and, consequently, the levels of cellular heme were directly related to COX activity. Supplementation with heme markedly increased PGE2 and cGMP synthesis. In all (6/6) of newborn SD rats injected with retrovirus LSN‐HOP‐HO‐1, both HO‐1 and neor transcripts were expressed in tissues. We hypothesize that degree of HO‐1 gene expression resulted in a differential rate of cellular heme‐dependent enzyme gene expression, which may play a vital role in maintaining cellular homeostasis. J. Cell. Biochem. 85: 410–421, 2002. © 2002 Wiley‐Liss, Inc.