Induction of arachidonate 12-lipoxygenase mRNA by epidermal growth factor in A431 cells

12(S)-Hydroxyeicosatetraenoic acid is biosynthesized from arachidonic acid by the microsomal fraction of human epidermoid carcinoma A431 cells, and the microsomal 12-lipoxygenase activity is enhanced by about 2-fold by epidermal growth factor (EGF) with a 10-h lag period (Chang, W. C., Ning, C. C., Lin, M. T., and Huang, J. D. (1992) J. Biol. Chem. 267, 3657-3666). The microsomal 12-lipoxygenase in A431 cells was only 3% active with linoleic acid as compared with arachidonic acid. The enzyme was immunoprecipitated by a monoclonal antibody against human platelet 12-lipoxygenase but not by that against porcine leukocyte enzyme. A 3.1-kilobase mRNA was detected in A431 cells by Northern blot analyses using cDNA probe of human platelet 12- lipoxygenase. EGF could increase the 12-lipoxygenase mRNA level by about 2- fold with a lag period of 10 h, which was well parallel with the increase in the enzyme activity. The induction of the 12-lipoxygenase mRNA by EGF was completely blocked by 35 μM cycloheximide, if present in culture medium during EGF treatment, indicating that a de novo protein biosynthesis was essential for EGF-induced 12-lipoxygenase mRNA expression. Our data provide the first evidence for the inducibility of human 12-lipoxygenase gene expression by a growth factor.