The fidelity of alternative splicing (AS) patterns is essential for growth development and cell fate determination. However, the scope of the molecular switches that regulate AS remains largely unexplored. Here we show that MEN1 is a previously unknown splicing regulatory factor. MEN1 deletion resulted in reprogramming of AS patterns in mouse lung tissue and human lung cancer cells, suggesting that MEN1 has a general function in regulating alternative precursor mRNA splicing. MEN1 altered exon skipping and the abundance of mRNA splicing isoforms of certain genes with suboptimal splice sites. Chromatin immunoprecipitation and chromosome walking assays revealed that MEN1 favored the accumulation of RNA polymerase II (Pol II) in regions encoding variant exons. Our data suggest that MEN1 regulates AS by slowing the Pol II elongation rate and that defects in these processes trigger R-loop formation, DNA damage accumulation and genome instability. Furthermore, we identified 28 MEN1-regulated exon-skipping events in lung cancer cells that were closely correlated with survival in patients with lung adenocarcinoma, and MEN1 deficiency sensitized lung cancer cells to splicing inhibitors. Collectively, these findings led to the identification of a novel biological role for menin in maintaining AS homeostasis and link this role to the regulation of cancer cell behavior.

Indoleamine 2, 3-dioxygenase 1 (IDO1) has been recognized as an enzyme involved in tryptophan catabolism with immunosuppressive ability. This study determined to investigate the impact of IDO1 on glioblastoma multiforme (GBM) cells. Here, we showed that the expression of IDO1 was markedly increased in patients with glioma and associated with GBM progression. IDO1 overexpression suppressed ferroptotic cell death, reduced ROS and lipid peroxide generation in GBM cells. IDO1 expression increased the SLC7A11 mRNA stability through FTO-dependent m6A methylation. Mechanistically, IDO1 promoted the AhR expression and nuclear translocation, thus facilitating AhR recruitment at the promoter regions of FTO gene and negatively regulating its transcription. These findings demonstrate that IDO1 facilitates GBM progression by inhibiting SLC7A11-dependent ferroptosis through an IDO1-AhR-FTO axis-mediated m6A methylation mechanism.

Background: Renal fibrosis is a serious condition that results in the development of chronic kidney diseases. The MEN1 gene is an epigenetic regulator that encodes the menin protein and its role in kidney tissue remains unclear.Methods: Kidney histology was examined on paraffin sections stained with hematoxylin‐eosin staining. Masson’s trichrome staining and Sirius red staining were used to analyze renal fibrosis. Gene and protein expression were determined by quantitative real‐time PCR (qPCR) and Western blot, respectively. Immunohistochemistry staining in the kidney tissues from mice or patients was used to evaluate protein levels. Flow cytometry was used to analyze the cell cycle distributions and apoptosis. RNA‐sequencing was performed for differential expression genes in the kidney tissues of the Men1f/f and Men1∆/∆ mice. Chromatin immunoprecipitation sequencing (ChIP‐seq) was carried out for identification of menin‐ and H3K4me3‐enriched regions within the whole genome in the mouse kidney tissue. ChIP‐qPCR assays were performed for occupancy of menin and H3K4me3 at the gene promoter regions. Luciferase reporter assay was used to detect the promoter activity. The exacerbated unilateral ureteral obstruction (UUO) models in the Men1f/f and Men1∆/∆ mice were used to assess the pharmacological effects of rh‐HGF on renal fibrosis.Results: The expression of MEN1 is reduce in kidney tissues of fibrotic mouse and human diabetic patients and treatment with fibrotic factor results in the downregulation of MEN1 expression in renal tubular epithelial cells (RTECs). Disruption of MEN1 in RTECs leads to high expression of α‐SMA and Collagen 1, whereas MEN1 overexpression restrains epithelial‐to‐mesenchymal transition (EMT) induced by TGF‐β treatment. Conditional knockout of MEN1 resulted in chronic renal fibrosis and UUO‐induced tubulointerstitial fibrosis (TIF), which is associated with an increased induction of EMT, G2/M arrest and JNK signaling. Mechanistically, menin recruits and increases H3K4me3 at the promoter regions of hepatocyte growth factor (HGF) and a disintegrin and metalloproteinase with thrombospondin motifs 5 (Adamts5) genes and enhances their transcriptional activation. In the UUO mice model, exogenous HGF restored the expression of Adamts5 and ameliorated renal fibrosis induced by Men1 deficiency.Conclusions: These findings demonstrate that MEN1 is an essential antifibrotic factor in renal fibrogenesis and could be a potential target for antifibrotic therapy.

Hepatocellular carcinoma (HCC) is a highly lethal liver cancer with complex pathogenesis intertwined with metabolic and mitochondrial dysfunction. MEN1/menin is a protein with context-dependent functions in liver diseases. While MEN1 has been linked to HCC progression and mitochondrial homeostasis, its precise regulatory mechanism in these processes remains incompletely understood. Here, we report that MEN1 localizes to the outer mitochondrial membrane (OMM) in HCC cells, which is mediated by its N-terminal mitochondrial targeting sequence and the TOMM20 translocase complex. In a genetically engineered DEN- and CCl₄-induced HCC mouse model, hepatocyte-specific men1 deficiency significantly suppressed tumorigenesis, a phenotype associated with impaired mitochondrial homeostasis. Mechanistically, MEN1 deficiency disrupted mitochondrial function by manifesting as promoted mitochondrial fission, impaired oxidative phosphorylation, reduced ATP levels, and elevated reactive oxygen species during energy stress. Critically, MEN1 loss inhibited mitophagy via downregulating the PINK1-PRKN/Parkin pathway, which impaired clearance of dysfunctional mitochondria and promotes their cytotoxic accumulation. Moreover, MEN1 expression was upregulated in human HCC tissues, correlated with poor clinical outcomes and was positively associated with autophagy signatures. Notably, pharmacological activation of mitophagy reversed the tumor-suppressive effects of MEN1 deficiency in vitro and in vivo. These findings identified a noncanonical role of mitochondrial MEN1 in driving HCC progression via regulating mitophagy homeostasis, and highlight the MEN1-mitophagy axis as a potential therapeutic target for HCC. Abbreviations: Alb-Cre: albumin promoter-driven recombinase Cre; Baf A1: bafilomycin A₁; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; CCl₄: carbon tetrachloride; Co-IP: co-immunoprecipitation; CQ: chloroquine; DEN: diethylnitrosamine; DNM1L: dynamin 1 like; DQ-BSA: self-quenched BODIPY-conjugated bovine serum albumin; Gal: galactose; GOT1/AST: glutamic-oxaloacetic transaminase 1; GPT/ALT: glutamic - pyruvic transaminase; HCC: hepatocellular carcinoma; WT: wild type; HMKO: hepatocyte-specific men1 knockout; IF: immunofluorescence; IHC: immunohistochemistry; IMM: inner mitochondrial membrane; KEGG: Kyoto Encyclopedia of Genes and Genomes; MEFs: mouse embryonic fibroblasts; MEN1-FL: full-length MEN1; MFF: mitochondrial fission factor; MFN1: mitofusin 1; MTS: mitochondrial targeting sequence; OCR: oxygen consumption rate; OMM: outer mitochondrial membrane; OXPHOS: oxidative phosphorylation; PINK1: PTEN induced kinase1; PRKAA1: protein kinase AMP-activated catalytic subunit alpha 1; PRKN: parkin RBR E3 ubiquitin protein ligase; qPCR: RNA extraction and quantitative polymerase chain reaction; RNA-seq: RNA-sequencing; ROS: reactive oxygen species; shMEN1: small hairpin RNA-mediated MEN1 knockdown; TCGA: The Cancer Genome Atlas; TEM: transmission electron microscopy; TOMM20: translocase of outer mitochondrial membrane 20.