Essential role of mitogen-activated protein kinase pathway and c-Jun induction in epidermal growth factor-induced gene expression of human 12-lipoxygenase

The role of mitogen-activated protein kinase signaling and the transcriptio n factor c-Jun in epidermal growth factor (EGF)-induced expression of 12-li poxygenase in human epidermoid carcinoma A431 cells was studied. EGF increa sed the activation of extracellular signal-regulated kinase (ERK) and c-Jun amino terminal kinase (JNK) in a time-dependent manner. Treatment of the c ells with an mitogen-activated protein kinase kinase inhibitor, PD098059 (3 0 mu M), inhibited the EGF- and pSV2ras-induced expression of 12-lipoxygena se mRNA. Transfection of the cells with Ras, ERK2, Rac, JNK dominant negati ve mutants pMMrasDN, K52R ERK2, RacN17, and mJNK all inhibited the EGF- ind uced promoter activation of the 12-lipoxygenase gene. EGF induced the expre ssion of c-Jun and the activity of transcription factor activator protein 1 in cells, and these effects were blocked by the treatment with K52R ERK2 a nd mJNK. Overexpression of c-Jun increased the expression of 12-lipoxygenas e mRNA and enzyme activity. Furthermore, the Sp1-binding sites in the promo ter region of the 12-lipoxygenase gene were requisite for c-Jun response, w hich was similar to that previously observed in EGF response. The results i ndicate that the EGF- induced expression of 12-lipoxygenase in A431 cells w as mediated through the Ras-ERK and Ras-Rac-JNK signal pathways. Subsequent induction of c-Jun led by ERK and JNK activation was essential for this EG F response.