Induction of 12‐lipoxygenase expression by transforming growth factor‐α in human epidermoid carcinoma A431 cells

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Abstract
Transforming growth factor-α (TGF-α) increased the expression of 12-lipoxygenase activity in a time-dependent manner in human epidermoid carcinoma A431 cells. The increase of 12-lipoxygenase activity was accompanied by an increase in 12-lipoxygenase mRNA. The effect of TGF-α on the promoter activation of 12-lipoxygenase gene was analyzed by using the luciferase fusion vectors. A dose-dependent effect of TGF-α on the reporter activity was observed, which paralleled with its effect on enzyme activity. Transient transfection with a series of 5′-deleted constructs showed that the 5′-flanking region spanning from −224 to −100 bp from translation starting site played an important role for TGF-α response. Site-directed mutagenesis and gel mobility shift assay indicated that two Sp1 binding sequences residing at −158 to −150 bp and −123 to −114 bp were responsible for the TGF-α in activation of human 12-lipoxygenase gene transcription. Expression of Sp1, but not Sp3, stimulated the promoter activity of 12-lipoxygenase in SL2 cells, indicating that the binding of Sp1 with Sp1 binding sequences played a significant role in the regulation of 12-lipoxygenase gene.