Estrogen receptor alpha promotes smoking-carcinogen-induced lung carcinogenesis via cytochrome P450 1B1

Smoking carcinogen N-nitrosamines such as 4-methylnitrosamino-l-3-pyridyl-butanone (NNK) require metabolic activation to exert their genotoxicity. The first activation step is mainly catalyzed by cytochrome P450 (CYP) family. Estrogen receptor alpha (ER alpha) plays a role in lung pathology. The association between them is unknown. In this study, we explored the relationship and function of CYP1B1 and ER alpha in NNK-induced lung tumorigenesis. CYP1B1 and ER alpha expression was analyzed in human lung cancer tissues and NNK-induced lung tumor of A/J mice. Cell lines NCI-H23 and NCI-H460 were employed to further study the responsible mechanisms using various cellular and molecular approaches. Our in vivo experiments demonstrated that CYP1B1 and ER alpha were over-expressed at the early stage of NNK-induced lung tumorigenesis. Microarray analysis found that ER alpha was involved in the extracellular-signal-regulated kinase (ERK)/MAPK pathway. NNK activated RAS/ERK/AP1 as it remarkably increased the levels of p-ERK, c-Fos, and c-Jun but inhibited multiple negative regulators of Ras/ERK/AP1, Pdcd4, Spry1, Spry2, and Btg2 through up-regulating miR21. Both CYP1B1 siRNA and ERK-specific inhibitor U0126 suppressed NNK-mediated ER alpha up-regulation, suggesting that ER alpha was downstream of CYP1B1 and ERK. ERK inactivation led to the accumulation of CYP1B1, indicating that CYP1B1 was upstream of ERK activation. Inhibition of ERK or ER alpha decreased NNK-induced cell proliferation. Blockage of CYP1B1 or ER alpha induced apoptosis of lung cancer cells. Collectively, NNK-mediated ER alpha induction is via CYP1B1 and ERK and contributes to the lung carcinogenesis. The inhibition of CYP1B1, ERK, or ER alpha may arrest the lung cancer cell growth, implicating a pivotal strategy for the treatment of lung cancer. Key messages Smoking carcinogen NNK requires metabolic activation to exert their genotoxicity. CYP1B1 is the enzyme to catalyze NNK. NNK activates CYP1B1 and ERK to induce ER alpha. Inhibition of CYP1B1, ERK, or ER alpha arrests the lung cancer cell growth.