The human cyclooxygenase-2 (Cox-2) cDNA was cloned and characterized from human umbilical vein endothelial cells (HUVEC). The cDNA encodes a 604-amino acid polypeptide that is 61% identical to the previously isolated human Cox-1 polypeptide. In vitro translation of the hCox-2 transcript in rabbit reticulocyte lysates produced a 70-kDa protein that is immunoprecipitated by antiserum to ovine Cox. Expression of the hCox-2 open reading frame in Cos-7 monkey kidney cells resulted in cyclooxygenase activity. hCox-2 cDNA hybridizes to a 4.5-kilobase mRNA species in HUVEC, whereas hCox-1 cDNA hybridizes to 3- and 5.3-kilobase species. Both Cox-1 and Cox-2 mRNAs are expressed in HUVEC, vascular smooth muscle cells, monocytes, and fibroblasts. Cox-2 mRNA was preferentially induced by phorbol 12-myristate 13-acetate and lipopolysaccharide in human endothelial cells and monocytes. These data demonstrate that the Cox enzyme is encoded by at least two genes that are expressed and differentially regulated in a variety of cell types. High-level induction of the hCox-2 transcript in mesenchymal-derived inflammatory cells suggests a role in inflammatory conditions. Cyclooxygenase (Cox) is a key enzyme in the synthesis of inflammatory prostaglandins. Growth factors, cytokines, and tumor promoters induce Cox activity. The human Cox-2 gene was cloned from HUVEC. The hCox-2 cDNA encodes a 604-amino acid polypeptide that is 61% identical to hCox-1. In vitro translation of hCox-2 produced a 70-kDa protein that is immunoprecipitated by antiserum to ovine Cox. Expression of hCox-2 in Cos-7 cells resulted in cyclooxygenase activity. hCox-2 mRNA is expressed in HUVEC, vascular smooth muscle cells, monocytes, and fibroblasts. Cox-2 mRNA is preferentially induced by PMA and LPS. These findings suggest that Cox is encoded by at least two genes that are expressed and differentially regulated in various cell types. The hCox-2 cDNA encodes an enzymatically active Cox protein. Regulation of hCox-1 and -2 mRNA levels was studied. PMA induces hCox-2 mRNA more significantly than hCox-1. Cox-2 is expressed in various cell types, including monocytes, and is induced by LPS. These results indicate that Cox-2 isThe human cyclooxygenase-2 (Cox-2) cDNA was cloned and characterized from human umbilical vein endothelial cells (HUVEC). The cDNA encodes a 604-amino acid polypeptide that is 61% identical to the previously isolated human Cox-1 polypeptide. In vitro translation of the hCox-2 transcript in rabbit reticulocyte lysates produced a 70-kDa protein that is immunoprecipitated by antiserum to ovine Cox. Expression of the hCox-2 open reading frame in Cos-7 monkey kidney cells resulted in cyclooxygenase activity. hCox-2 cDNA hybridizes to a 4.5-kilobase mRNA species in HUVEC, whereas hCox-1 cDNA hybridizes to 3- and 5.3-kilobase species. Both Cox-1 and Cox-2 mRNAs are expressed in HUVEC, vascular smooth muscle cells, monocytes, and fibroblasts. Cox-2 mRNA was preferentially induced by phorbol 12-myristate 13-acetate and lipopolysaccharide in human endothelial cells and monocytes. These data demonstrate that the Cox enzyme is encoded by at least two genes that are expressed and differentially regulated in a variety of cell types. High-level induction of the hCox-2 transcript in mesenchymal-derived inflammatory cells suggests a role in inflammatory conditions. Cyclooxygenase (Cox) is a key enzyme in the synthesis of inflammatory prostaglandins. Growth factors, cytokines, and tumor promoters induce Cox activity. The human Cox-2 gene was cloned from HUVEC. The hCox-2 cDNA encodes a 604-amino acid polypeptide that is 61% identical to hCox-1. In vitro translation of hCox-2 produced a 70-kDa protein that is immunoprecipitated by antiserum to ovine Cox. Expression of hCox-2 in Cos-7 cells resulted in cyclooxygenase activity. hCox-2 mRNA is expressed in HUVEC, vascular smooth muscle cells, monocytes, and fibroblasts. Cox-2 mRNA is preferentially induced by PMA and LPS. These findings suggest that Cox is encoded by at least two genes that are expressed and differentially regulated in various cell types. The hCox-2 cDNA encodes an enzymatically active Cox protein. Regulation of hCox-1 and -2 mRNA levels was studied. PMA induces hCox-2 mRNA more significantly than hCox-1. Cox-2 is expressed in various cell types, including monocytes, and is induced by LPS. These results indicate that Cox-2 is