Interplay between Menin and K-Ras in Regulating Lung Adenocarcinoma

Shan-Hua Li,Xianxin Hua,Zi-Jie Feng,Bin Xu,Yuan Wu,Smita Matkar,Guang-Hui Jin,Hong-Bin Duan,Xiao Lin,Shu-Bin Gao

doi:10.1074/jbc.m112.382416

Abstract

MEN1, which encodes the nuclear protein menin, acts as a tumor suppressor in lung cancer and is often inactivated in human primary lung adenocarcinoma. Here, we show that the inactivation of MEN1 is associated with increased DNA methylation at the MEN1 promoter by K-Ras. On one hand, the activated K-Ras up-regulates the expression of DNA methyltransferases and enhances the binding of DNA methyltransferase 1 to the MEN1 promoter, leading to increased DNA methylation at the MEN1 gene in lung cancer cells; on the other hand, menin reduces the level of active Ras-GTP at least partly by preventing GRB2 and SOS1 from binding to Ras, without affecting the expression of GRB2 and SOS1. In human lung adenocarcinoma samples, we further demonstrate that reduced menin expression is associated with the enhanced expression of Ras (p < 0.05). Finally, excision of the Men1 gene markedly accelerates the K-Ras(G12D)-induced tumor formation in the Men1(f/f);K-Ras(G12D/+);Cre ER mouse model. Together, these findings uncover a previously unknown link between activated K-Ras and menin, an important interplay governing tumor activation and suppression in the development of lung cancer.

Highlights

The role of MEN1 gene in development of lung cancer is poorly understood
To determine whether the reduced menin expression is correlated with MEN1 mutations in the lung cancer samples, we extracted the genomic DNA from six paraffin-embedded lung adenocarcinoma samples in which menin expression was reduced
Previous studies have identified that multiple genes, including TP53, CDKN2A, epidermal growth factor receptor (EGFR), and K-Ras were involved in the development of lung cancer [1,2,3]

Summary

Background

The role of MEN1 gene in development of lung cancer is poorly understood. Results: K-Ras inhibits menin expression via increasing DNA methylation, whereas menin inhibits Ras-mediated signaling via suppressing activation of Ras. Phosphorylation of Rb protein by either CDK2 or CDK4/6 sites results in activation of the activity of pro-proliferative transcription factor E2Fs, and the phosphorylation of Rb is significantly increased in bronchial epithelia and tumor cells derived from p18Ϫ/Ϫ;Men1ϩ/Ϫ mice [15] These findings suggest that menin is important for repressing the development of lung cancer, but the molecular mechanisms remain unclear. Excision of the Men gene can accelerate the tumor formation induced by temporally controlled induction K-RasG12D in Men1f/f;KRasG12D/ϩ;Cre ER mouse model Together, these findings unravel a previously unknown link between the oncogene K-Ras and tumor suppressor menin, whose intertwining may play a crucial role in regulating the development of lung cancer

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION