Ouyang Miao, Su Weijie, Xiao Lan, Rao Jaladanki N, Jiang Liping, Li Yanwu, Turner Douglas J, Gorospe Myriam, Wang Jian-Ying
*Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD, U.S.A.
‡Laboratory of Genetics, National Institute on Aging-IRP, National Institutes of Health, Baltimore, MD, U.S.A.
Biochem J. 2015 Jan 15;465(2):315-23. doi: 10.1042/BJ20141028.
Menin regulates distinct cellular functions by regulating gene transcription through its interaction with partner transcription factors, but the exact mechanisms that control menin levels remain largely unknown. In the present study we report that Men1 mRNA, encoding menin, is a novel target of miR-29b and that miR-29b/Men1 mRNA association regulates menin expression post-transcriptionally in rat intestinal epithelial cells (IECs). Overexpression of a miR-29b precursor lowered the levels of Men1 mRNA modestly, but reduced new synthesis of menin robustly; conversely, antagonism of miR-29b enhanced menin protein synthesis and steady-state levels. The repressive effect of miR-29b on menin expression was mediated through a single binding site in the coding region of Men1 mRNA, because point mutation of this site prevented miR-29b-induced repression of menin translation. Increasing cellular polyamines due to overexpression of ornithine decarboxylase (ODC) enhanced menin translation by reducing miR-29b, whereas polyamine depletion by inhibiting ODC increased it, thus suppressing menin expression. Moreover, an increase in menin abundance in an miR-29b-silenced population of IECs led to increased sensitivity to apoptosis, which was prevented by silencing menin. These findings indicate that miR-29b represses translation of Men1 mRNA, in turn affecting intestinal epithelial homoeostasis by altering IEC apoptosis.
Menin通过与伙伴转录因子相互作用来调节基因转录，从而调控不同的细胞功能，但控制Menin水平的具体机制仍 largely未知。在本研究中，我们报告编码Menin的Men1 mRNA是miR - 29b的一个新靶点，并且miR - 29b/Men1 mRNA结合在转录后调控大鼠肠上皮细胞（IECs）中Menin的表达。miR - 29b前体的过表达适度降低了Men1 mRNA的水平，但显著减少了Menin的新合成；相反，miR - 29b的拮抗作用增强了Menin蛋白的合成和稳态水平。miR - 29b对Menin表达的抑制作用是通过Men1 mRNA编码区的一个单一结合位点介导的，因为该位点的点突变阻止了miR - 29b诱导的Menin翻译抑制。由于鸟氨酸脱羧酶（ODC）过表达导致细胞多胺增加，通过减少miR - 29b增强了Menin的翻译，而通过抑制ODC使多胺耗竭则增加了miR - 29b，从而抑制了Menin的表达。此外，在miR - 29b沉默的IECs群体中Menin丰度的增加导致对凋亡的敏感性增加，而通过沉默Menin可防止这种情况。这些发现表明miR - 29b抑制Men1 mRNA的翻译，进而通过改变IEC凋亡影响肠上皮稳态。
