Hepatic menin recruits SIRT1 to control liver steatosis through histone deacetylation

BACKGROUND & AIMS

The development and progression of non-alcoholic fatty liver disease are associated with aging, obesity, and type 2 diabetes. Understanding the precise regulatory networks of this process will contribute to novel therapeutic strategies.

METHODS

Hepatocyte-specific Men1 knockout mice were generated using Cre/loxP technology. Lipid and glucose metabolic phenotypes and mechanisms were investigated in aging and high-fat diet fed mice.

RESULTS

The expression of menin, encoded by multiple endocrine neoplasia 1 (Men1) gene, is reduced in the liver of aging mice. Hepatocyte-specific deletion of Men1 induces liver steatosis in aging mice. Menin deficiency promotes high-fat diet-induced liver steatosis in mice. Menin recruits SIRT1 to control hepatic CD36 expression and triglyceride accumulation through histone deacetylation.

CONCLUSIONS

Our work reveals that the adaptor protein menin is critical for the progression of hepatic steatosis during aging and metabolic imbalance.

Metabolic expressivity of human genetic variants: NMR metabotyping of MEN1 pathogenic mutants

Functional consequences of mutations in predisposition genes for familial cancer syndromes remain often elusive, especially when the corresponding gene products play pleiotropic functions and interact with numerous partners. Understanding the consequences of these genetic alterations requires access to their functional effects at the phenotypic level. Nuclear magnetic resonance (NMR) has emerged as a promising functional genomics probe, through its ability to monitor the consequences of genetic variations at the biochemical level. Here, we determine by NMR the metabolic perturbations associated with different disease-related mutations in the MEN1 gene, responsible for the multiple endocrine neoplasia syndrome, type 1 (MEN1), an example of hereditary cancer. The MEN1 gene encodes the Menin protein. Based on a cellular model that allows exogenous overexpression of either the wild type (WT) Menin protein or disease-related variant forms, we evaluate the feasibility of using metabolic profiles to discriminate cells with WT versus variant Menin overexpression. High-resolution magic angle spinning (HRMAS) NMR of whole cells allows to determine the metabolic features associated with overexpression of WT Menin as compared to the one of six different missense variants observed in MEN1 patients. We then identify several statistically significant individual metabolites associated with the metabolic signature of pathogenic versus WT variants. Whether such a metabolic phenotyping approach using cell lines could be exploited as a functional test in a human genetic cancer syndrome is further discussed.

SUMO modification of menin

Menin acts as contextual a tumor suppressor and a tumor promoter, partly via epigenetic regulation of gene transcription. While menin is phosphorylated, it remains unclear whether wild type menin has other post-translational modifications. Here, we report that menin is SUMOylated by SUMO1 in vivo and in vitro, and the SUMOylation is reduced by a SUMO protease. Lysine 591 of menin was covalently modified by SUMO1 and K591R mutation in menin blocked SUMOylation of the C-terminal part of menin in transfected cells. Full-length menin with K591 mutation was still SUMOylated in vivo, suggesting the existence of multiple SUMOylation sites. Menin K591R mutant or menin-SUMO fusion protein still retains the ability to regulate cell proliferation and the expression of the examined menin target genes.

Menin represses tumorigenesis via repressing cell proliferation

Multiple endocrine neoplasia type 1 (MEN1) results from mutations in the tumor suppressor gene, MEN1, which encodes nuclear protein menin. Menin is important for suppressing tumorigenesis in various endocrine and certain non-endocrine tissues. Although menin suppresses MEN1 through a variety of mechanisms including regulating apoptosis and DNA repair, the role of menin in regulating cell proliferation is one of the best-studied functions. Here, we focus on reviewing various mechanisms underlying menin-mediated inhibition of cell proliferation. Menin inhibits cell proliferation to repress MEN1 through multiple mechanisms. 1) Menin interacts with various histonemodifying enzymes, such as MLL, EZH2 and HDACs, to affect gene transcription, leading to repression of cell proliferation. 2) Menin also interacts with various transcription factors, such as JunD, NF-κB, PPARγ and VDR, to induce or suppress gene transcription. As these various transcription factors are known to regulate cell proliferation, their interaction with menin may be relevant to menin's role in inhibiting cell proliferation. 3) Menin inhibits cell proliferation via TGF-β signaling and Wnt/β-catenin signaling pathways. 4) Menin represses certain pro-proliferative factors involved in endocrine tumors such as IGFBP-2, IGF2 and PTHrP to repress cell proliferation. 5) Menin affects cell cycle progression to inhibit cell proliferation. This review is helpful in our understanding of the comprehensive mechanisms whereby menin represses MEN1 through inhibiting cell proliferation.

Molecular analysis of MEN1 expression in MCF7, T47D and MDA-MB 468 breast cancer cell lines treated with adriamycin using RT-PCR and immunocytochemistry

BACKGROUND AND THE PURPOSE OF THE STUDY

MEN1 is an important tumor suppressor gene that encodes a nuclear protein called menin. Recent data suggest that interactions between menin and other proteins have important roles in control of the cell cycle and apoptosis. In addition, estrogen receptor (ER), an important prognostic factor is differentially expressed in breast cancer cells. In this study the MEN1 gene and protein expression in MCF7, T47D and MDA-MB-468 breast cancer cell lines with different ER status following exposure to adriamycin (ADR) was investigated.

MATERIALS AND METHODS

Cytotoxicity of ADR on these cell lines was determined using MTT assay. The mRNA and protein levels were analyzed in tested cell lines using RT-PCR and immunocytochemistry (ICC) assays, respectively.

RESULTS

ADR cytotoxicity was highest on MDA-MB-468 and lowest on MCF7 cells. MEN1 mRNA showed significant decrease after ADR exposure only in the MDA-MB-468 cell line. Menin protein expression was higher in MDA-MB-468 and lower in MCF7 cells.

CONCLUSION

Differential molecular responses to adriamycin were observed in cancer cell lines. Molecular data also suggest that MEN1 as a new biomarker can be used in combination with current biomarkers for prediction of response to chemotherapy.