Expression of 15-Lipoxygenase-1 in Human Colorectal Cancer

Recently, we reported the induction of reticulocyte type 15-lipoxygenase (15-Lox-1) in a human colorectal carcinoma cell line that had been stimulated by butyrate to undergo apoptosis and cell differentiation (H. Kamitani et al., J. Biol. Chem., 273: 21569–21577, 1998). To determine if 15-Lox-1 is expressed in human colorectal cancer tissue, 21 matched pairs of colorectal tumor and adjacent normal tissue were examined by immunoblot analysis using specific antibodies for human 15-Lox-1, prostaglandin H synthase (also called cyclooxygenase, Cox)-1 and Cox-2. Eighteen of the 21 were found to have 15-Lox-1 in both tumor tissue and matched adjacent normal tissue, with the 15-Lox-1 expression being significantly higher in most of the tumor tissue. The expression of Cox-2 was also elevated in most tumors, whereas Cox-1 was frequently expressed at lower levels in the tumor tissue than in the paired normal tissue. Reverse-phase high-performance liquid chromatography analysis of arachidonate metabolites, formed on incubation of arachidonic acid with a crude enzyme preparation from the colon samples, revealed the formation of 15-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid with a much lower level of 12-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (15-hydroxy5Z,8Z,11Z,13E -eicosatetraenoic acid:12-hydroxy-5Z,8Z,10E,14Z -eicosatetraenoic acid, 6.5:1) which also indicate the presence of 15-Lox-1. Furthermore, reverse transcription-PCR with primers specific for human 15-Lox-1 or 15-Lox-2 cDNA indicated that 15-Lox-1 mRNA was present in the colorectal tumors. The sequence of the PCR product was identical to the human 15-Lox-1. Immunohistochemical studies showed 15-Lox-1 localization in the glandular epithelium of human colorectal tumor tissue. These results suggest that 15-Lox-1 is highly expressed in human colorectal cancer epithelial cells and that its expression may have a role in colorectal carcinogenesis.