Arachidonic acid released by PIK3CA mutant tumor cells triggers malignant transformation of colonic epithelium by inducing chromatin remodeling

Key gene mutations are essential for colorectal cancer (CRC) development; however, how the mutated tumor cells impact the surrounding normal cells to promote tumor progression has not been well defined. Here, we report that PIK3CA mutant tumor cells transmit oncogenic signals and result in malignant transformation of intestinal epithelial cells (IECs) via paracrine exosomal arachidonic acid (AA)-induced H3K4 trimethylation. Mechanistically, PIK3CA mutations sustain SGK3-FBW7-mediated stability of the cPLA2 protein, leading to the synthetic increase in AA, which is transported through exosome and accumulated in IECs. Transferred AA directly binds Menin and strengthens the interactions of Menin and MLL1/2 methyltransferase. Finally, the combination of VTP50469, an inhibitor of the Menin-MLL interaction, and alpelisib synergistically represses PDX tumors harboring PIK3CA mutations. Together, these findings unveil the metabolic link between PIK3CA mutant tumor cells and the IECs, highlighting AA as the potential target for the treatment of patients with CRC harboring PIK3CA mutations.

FXR/Menin-mediated epigenetic regulation of E2F3 expression controls β-cell proliferation and is increased in islets from diabetic GK rats after RYGB

Farnesoid X receptor (FXR) improves the function of islets, especially in the setting of Roux-en-Y gastric bypass (RYGB). Here we investigated how FXR activation regulates β-cell proliferation and explored the potential link between FXR signaling and the menin pathway in controlling E2F3 expression, a key transcription factor for controlling adult β-cell proliferation. Stimulation with the FXR agonist GW4064 or chenodeoxycholic acid (CDCA) increased E2F3 expression and β-cell proliferation. Consistently, E2F3 knockdown abolished GW4064-induced proliferation. Treatment with GW4064 increased E2F3 expression in β-cells via enhancing Steroid receptor coactivator-1 (SRC1) recruitment, increasing the pro-transcriptional acetylation of histone H3 at the E2f3 promoter. GW4064 treatment also decreased the association between FXR and menin, leading to the induction of FXR-mediated SRC1 recruitment. Mimicking the impact of FXR agonists, RYGB also increased E2F3 expression and β-cell proliferation in GK rats and SD rats. These findings unravel the crucial role of the FXR/menin signaling in epigenetically controlling E2F3 expression and β-cell proliferation, a mechanism possibly underlying RYGB-induced β-cell proliferation.

Fyn-mediated phosphorylation of Menin disrupts telomere maintenance in stem cells

Telomeres protect chromosome ends and determine the replication potential of dividing cells. The canonical telomere sequence TTAGGG is synthesized by telomerase holoenzyme, which maintains telomere length in proliferative stem cells. Although the core components of telomerase are well-defined, mechanisms of telomerase regulation are still under investigation. We report a novel role for the Src family kinase Fyn, which disrupts telomere maintenance in stem cells by phosphorylating the scaffold protein Menin. We found that Fyn knockdown prevented telomere erosion in human and mouse stem cells, validating the results with four telomere measurement techniques. We show that Fyn phosphorylates Menin at tyrosine 603 (Y603), which increases Menin's SUMO1 modification, C-terminal stability, and importantly, its association with the telomerase RNA component (TR). Using mass spectrometry, immunoprecipitation, and immunofluorescence experiments we found that SUMO1-Menin decreases TR's association with telomerase subunit Dyskerin, suggesting that Fyn's phosphorylation of Menin induces telomerase subunit mislocalization and may compromise telomerase function at telomeres. Importantly, we find that Fyn inhibition reduces accelerated telomere shortening in human iPSCs harboring mutations for dyskeratosis congenita.

Itaconate inhibits corticosterone-induced necroptosis and neuroinflammation via up-regulating menin in HT22 cells

Corticosterone (CORT) damages hippocampal neurons as well as induces neuroinflammation. The tricarboxylic acid cycle metabolite itaconate has an anti-inflammatory role. Necroptosis is a form of programmed cell death, also known as inflammatory cell death. Menin is a multifunctional scaffold protein, which deficiency aggravates neuroinflammation. In this study, we explored whether itaconate inhibits CORT-induced neuroinflammation as well as necroptosis and further investigated the mediatory role of Menin in this protective effect of itaconate by using an exposure of CORT to HT22 cells (a hippocampal neuronal cell line). The viability of HT22 cells was examined by the cell counting kit 8 (CCK-8). The morphology of HT22 cells was observed by transmission electron microscope (TEM). The expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) were evaluated by western blotting. The contents of inflammatory factors were detected by an enzyme-linked immunosorbent assay (ELISA) kit. Our results showed that CORT increases the contents of pro-inflammatory factors (IL-1β, TNF-α) as well as decreases the contents of anti-inflammatory factors (IL-4, IL-10) in HT22 cells. We also found that CORT increases the expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) and decreases the cell viability in HT22 cells, indicating that CORT induces necroptosis in HT22 cells. Itaconate improves CORT-induced neuroinflammation and necroptosis. Furthermore, itaconate upregulates the expression of Menin in CORT-exposed HT22 cells. Importantly, silencing Menin abolishes the antagonistic effect of itaconate on CORT-induced necroptosis and neuroinflammation. In brief, these results indicated that itaconate protects HT22 cells against CORT-induced neuroinflammation and necroptosis via upregulating Menin.

Syndromic MEN1 parathyroid adenomas consist of both subclonal nodules and clonally independent tumors

Primary hyperparathyroidism with parathyroid tumors is a typical manifestation of Multiple Endocrine Neoplasia Type 1 (MEN1) and is historically termed "primary hyperplasia". Whether these tumors represent a multi-glandular clonal disease or hyperplasia has not been robustly proven so far. Loss of Menin protein expression is associated with inactivation of both alleles and a good surrogate for a MEN1 gene mutation. The cyclin-dependent kinase inhibitor 1B (CDKN1B) gene is mutated in MEN4 and encodes for protein p27 whose expression is poorly studied in the syndromic MEN1 setting.Here, we analyzed histomorphology and protein expression of Menin and p27 in parathyroid adenomas of 25 patients of two independent, well-characterized MEN1 cohorts. The pattern of loss of heterozygosity (LOH) was assessed by fluorescence in situ hybridization (FISH) in one MEN1-associated parathyroid adenoma. Further, next-generation sequencing (NGS) was performed on eleven nodules of four MEN1 patients.Morphologically, the majority of MEN1 adenomas consisted of multiple distinct nodules, in which Menin expression was mostly lost and p27 protein expression reduced. FISH analysis revealed that most nodules exhibited MEN1 loss, with or without the loss of centromere 11. NGS demonstrated both subclonal evolution and the existence of clonally unrelated tumors.Syndromic MEN1 parathyroid adenomas therefore consist of multiple clones with subclones, which supports the current concept of the novel WHO classification of parathyroid tumors (2022). p27 expression was lost in a large fraction of MEN1 parathyroids and must therefore be used with caution in suggesting MEN4.

Evaluation of the prognostic and therapeutic potential of inhibin beta B for oral squamous cell carcinoma

Background/purpose

Oral squamous cell carcinoma (OSCC) is a common cancer worldwide, and its metastasis is difficult to predict and prevent. Inhibin beta B (INHBB) protein has been linked to cancer prognosis and epithelial-mesenchymal transition (EMT). However, previous study about INHBB expression focused on patients in a single region while the risk factors vary among regions. This study aimed to provide a broader perspective on INHBB expression in OSCC.

Materials and methods

Tissue micro-arrays comprising 118 specimens were subjected to immunohistochemistry, and all slides were quantified using StrataQuest software.

Results

The ratio of INHBB-positive cells to total cells was significantly higher in OSCC samples than in normal samples, and the intensity of INHBB expression was significantly greater in the late-stage OSCC. After classifying specimens into high and low INHBB expression groups, a significant association with clinical staging was found. Though a previous study suggested that menin regulates INHBB, menin expression was not detected in specimens.

Conclusion

The ratio of INHBB-positive cells in OSCC may be druggable for targeting tumor cells or assisting in diagnosis, and the intensity of INHBB expression may provide prognostic information for predicting potential metastasis. Moreover, the regulatory mechanism of INHBB in OSCC remains unclear and requires further investigation.

Therapeutic targeting in pediatric acute myeloid leukemia with aberrant HOX/MEIS1 expression

Despite advances in the clinical management of childhood acute myeloid leukemia (AML) during the last decades, outcome remains fatal in approximately one third of patients. Primary chemoresistance, relapse and acute and long-term toxicities to conventional myelosuppressive therapies still constitute significant challenges and emphasize the unmet need for effective targeted therapies. Years of scientific efforts have translated into extensive insights on the heterogeneous spectrum of genetics and oncogenic signaling pathways of AML and identified a subset of patients characterized by upregulation of HOXA and HOXB homeobox genes and myeloid ecotropic virus insertion site 1 (MEIS1). Aberrant HOXA/MEIS1 expression is associated with genotypes such as rearrangements in Histone-lysine N-methyltransferase 2A (KMT2A-r), nucleoporin 98 (NUP98-r) and mutated nucleophosmin (NPM1c) that are found in approximately one third of children with AML. AML with upregulated HOXA/MEIS1 shares a number of molecular vulnerabilities amenable to recently developed molecules targeting the assembly of protein complexes or transcriptional regulators. The interaction between the nuclear scaffold protein menin and KMT2A has gained particular interest and constitutes a molecular dependency for maintenance of the HOXA/MEIS1 transcription program. Menin inhibitors disrupt the menin-KMT2A complex in preclinical models of KMT2A-r, NUP98-r and NPM1c acute leukemias and its occupancy at target genes leading to leukemic cell differentiation and apoptosis. Early-phase clinical trials are either ongoing or in development and preliminary data suggests tolerable toxicities and encouraging efficacy of menin inhibitors in adults with relapsed or refractory KMT2A-r and NPM1c AML. The Pediatric Acute Leukemia/European Pediatric Acute Leukemia (PedAL/EUPAL) project is focused to advance and coordinate informative clinical trials with new agents and constitute an ideal framework for testing of menin inhibitors in pediatric study populations. Menin inhibitors in combination with standard chemotherapy or other targeting agents may enhance anti-leukemic effects and constitute rational treatment strategies for select genotypes of childhood AML, and provide enhanced safety to avoid differentiation syndrome. In this review, we discuss the pathophysiological mechanisms in KMT2A-r, NUP98-r and NPM1c AML, emerging molecules targeting the HOXA/MEIS1 transcription program with menin inhibitors as the most prominent examples and future therapeutic implications of these agents in childhood AML.

Menin orchestrates hepatic glucose and fatty acid uptake via deploying the cellular translocation of SIRT1 and PPARγ

BACKGROUND

Menin is a scaffold protein encoded by the Men1 gene, which interacts with various transcriptional proteins to activate or repress cellular processes and is a key mediator in multiple organs. Both liver-specific and hepatocyte-specific Menin deficiency promotes high-fat diet-induced liver steatosis in mice, as well as insulin resistance and type 2 diabetic phenotype. The potential link between Menin and hepatic metabolism homeostasis may provide new insights into the mechanism of fatty liver disease.

RESULTS

Disturbance of hepatic Menin expression impacts metabolic pathways associated with non-alcoholic fatty liver disease (NAFLD), including the FoxO signaling pathway, which is similar to that observed in both oleic acid-induced fatty hepatocytes model and biopsied fatty liver tissues, but with elevated hepatic Menin expression and inhibited FABP1. Higher levels of Menin facilitate glucose uptake while restraining fatty acid uptake. Menin targets the expression of FABP3/4/5 and also CD36 or GK, PCK by binding to their promoter regions, while recruiting and deploying the cellular localization of PPARγ and SIRT1 in the nucleus and cytoplasm. Accordingly, Menin binds to PPARγ and/or FoxO1 in hepatocytes, and orchestrates hepatic glucose and fatty acid uptake by recruiting SIRT1.

CONCLUSION

Menin plays an orchestration role as a transcriptional activator and/or repressor to target downstream gene expression levels involved in hepatic energy uptake by interacting with the cellular energy sensor SIRT1, PPARγ, and/or FoxO1 and deploying their translocations between the cytoplasm and nucleus, thereby maintaining metabolic homeostasis. These findings provide more evidence suggesting Menin could be targeted for the treatment of hepatic steatosis, NAFLD or metabolic dysfunction-associated fatty liver disease (MAFLD), and even other hepatic diseases.

Sporadic pituitary adenoma with somatic double-hit loss of MEN1

PURPOSE

Pituitary adenomas commonly arise in patients with MEN1 syndrome, an autosomal dominant condition predisposing to neuroendocrine tumor formation, and typically diagnosed in patients with a relevant family cancer history. In these patients with existing germline loss of MEN1 on one allele, somatic loss of the second MEN1 allele leads to complete loss of the MEN1 protein, menin, and subsequent tumor formation.

METHODS

Whole exome sequencing was performed on the tumor and matching blood under an institutional board approved protocol. DNA extraction and analysis was conducted according to previously described methods.

RESULTS

We describe a 23 year-old patient with no significant past medical history or relevant family history who underwent surgical resection of a symptomatic and medically resistant prolactinoma. Whole exome sequencing of tumor and blood samples revealed somatic loss of MEN1 at both alleles, suggesting a double hit mechanism, with no underlying germline MEN1 mutation.

CONCLUSION

To our knowledge, this is the first case of pituitary adenoma to arise from somatic loss of MEN1 and in the absence of an underlying germline MEN1 mutation.

Senescent CD8+ T cells acquire NK cell-like innate functions to promote antitumor immunity

It has been suggested that aging of the immune system (immunosenescence) results in a decline in the acquired immune response, which is associated with an increase in age-related tumorigenesis. T-cell senescence plays a critical role in immunosenescence and is involved in the age-related decline of the immune function, which increases susceptibility to certain cancers. However, it has been shown that CD8⁺ T cells with the senescent T-cell phenotype acquire an natural killer (NK) cell-like function and are involved in tumor elimination. Therefore, the role of senescent CD8⁺ T cells in tumor immunity remains to be elucidated. In this study, we investigated the role of senescent CD8⁺ T cells in tumor immunity. In a murine model of transferred with B16 melanoma, lung metastasis was significantly suppressed in aged mice (age ≥30 weeks) in comparison to young mice (age 6-10 weeks). We evaluated the cytotoxic activity of CD8⁺ T cells in vitro and found that CD8⁺ T cells from aged mice activated in vitro exhibited increased cytotoxic activity in comparison to those from young mice. We used Menin-deficient effector T cells as a model for senescent CD8⁺ T cells and found that cytotoxic activity and the expression of NK receptors were upregulated in Menin-deficient senescent CD8⁺ T cells. Furthermore, Menin-deficient CD8⁺ T cells can eliminate tumor cells in an antigen-independent manner. These results suggest that senescent effector CD8⁺ T cells may contribute to tumor immunity in the elderly by acquiring NK-like innate immune functions, such as antigen-independent cytotoxic activity.

Multiple Endocrine Neoplasia Type 1 Syndrome Pancreatic Neuroendocrine Tumor Genotype/Phenotype: Is There Any Advance on Predicting or Preventing?

Multiple endocrine neoplasia type 1 syndrome (MEN1) is a disease caused by mutations in the MEN1 tumor suppressor gene leading to hyperparathyroidism, pituitary adenomas, and entero-pancreatic neuroendocrine tumors. Pancreatic neuroendocrine tumors (PNETs) are a major cause of mortality in patients with MEN1. Identification of consistent genotype-phenotype correlations has remained elusive, but MEN1 mutations in exons 2, 9, and 10 may be associated with metastatic PNETs; patients with these mutations may benefit from more intensive surveillance and aggressive treatment. In addition, epigenetic differences between MEN1-associated PNETs and sporadic PNETs are beginning to emerge, but further investigation is required to establish clear phenotypic associations.

Translational advances in the treatment of childhood acute lymphoblastic leukemia: narrative review of current and emerging molecular and immunotherapies

Background and Objective

Acute lymphoblastic leukemia (ALL) is the most common hematologic malignancy of lymphoid origin in children. The prognosis for newly diagnosed ALL in the pediatric population is generally favorable, with a 5-year overall survival rate of more than 90%. Though conventional therapy has led to meaningful improvements in cure rates for new-onset pediatric ALL, one-third of patients still experience a relapse or refractory disease, contributing to a significant cause of pediatric cancer-related mortality.

Methods

An extensive literature review was undertaken via various databases of medical literature, focusing on both results of larger clinical trials, but also with evaluation of recent abstract publications at large hematologic conferences.

Key Content and Findings

Remission is achievable in most of these patients by re-induction with currently available therapies, but the long-term overall survival rate is deemed suboptimal and remains a therapeutic challenge. As part of never-ceasing efforts to improve pediatric ALL outcomes, newer modalities, including targeted molecular therapies as well as immunotherapy, and chimeric antigen receptor (CAR) T-cell therapy, are currently being employed to increase treatment effectiveness as well as lessen the side effects from conventional chemotherapy. These approaches explore the use of early genome-based disease characterization and medications developed against actionable molecular targets.

Conclusions

Additional clinical research is nonetheless required to learn more about the potentially harmful effects of targeted therapies and investigate the possibility of these agents replacing or decreasing the use of conventional chemotherapy in treating pediatric ALL.

Loss of tumor suppressor menin expression in high grade cholangiocarcinomas

BACKGROUND

MEN1, which codes for the protein menin, is a tumor suppressor in neuroendocrine tissue. In cholangiocarcinoma (CCA) cell lines the overexpression of menin decreased proliferation, angiogenesis, migration, and invasion in vitro and in xenografts, but its expression in CCA tumor tissue samples is not established.

OBJECTIVE

Determine whether the expression of menin correlates with disease progression in patient samples of CCA in a tissue microarray (TMA) by immunohistochemical (IHC) staining.

RESULTS

IHC analysis of 97 biopsies revealed that low-grade tumors (Grade I) exhibited intense, diffuse, finely granular nuclear menin immunoreactivity with a pronounced linear perinuclear pattern (mean IHC score = 2.00), whereas high-grade tumors (Grade III) mostly lacked such staining (mean IHC score = 0.35). Collectively, there was a significant inverse association between tumor grade and menin staining (P = 0.0005). We also found a significant association between fibrosis status and menin staining, in that, 81.2% (56/69) of patients without fibrosis had no menin staining, whereas 92.9% (26/28) patients with fibrosis exhibited menin staining (P < 0.0001). No association was found between fibrosis status and grade. Overall, menin expression is inversely associated with tumor grade and positively associated with fibrosis status.

HSP27/Menin Expression as New Prognostic Serum Biomarkers of Prostate Cancer Aggressiveness Independent of PSA

The screening of PCa is based on two tests, the total PSA test and the rectal examination. However, PSA is not specific for PCa stage confirmation, leading in false positive result and involving PCa over-diagnosis and over-treatment. HSP27 and Menin have been found to be overexpressed in a wide range of human cancers. Recent studies showed how HSP27 interacts with and stabilizes Menin to lead PCa progression and treatment resistance. The purpose of our study was to evaluate the correlation of HSP27 and Menin molecular expression, and their prognosis value in PCa with respect to clinicopathological features. Elisa was employed to measure serum HSP27 and Menin concentrations in 73 PCa patients and 80 healthy individuals. Immunohistochemistry (IHC) was used to determine HSP27 and Menin tissue expression in 57 tumors and 4 Benign Prostatic Hyperplasia (BPH) tissues. Serum HSP27 expression correlated with its tissue expression in all PCa patients, whereas serum Menin expression correlated only with tissue expression in aggressive PCa patients. Moreover, the results showed a positive correlation between HSP27 and Menin either in serum (r = 0.269; p = 0.021) or in tissue (r = 0.561; p < 0.0001). In aggressive PCa, serum expression of HSP27 and Menin was positively correlated (r = 0.664; R = 0.441; p = 0.001). The correlation between HSP27 and Menin expression in tissue was found only in patients with aggressive PCa (r = 0.606; R = 0.367; p = 0.004). Statistical analysis showed that the expression of both biomarkers was positively correlated with the hormone resistance or sensitivity, tumor aggressiveness, metastasis, Gleason Score, death and did not significantly correlate with age and PSA. Survival was illustrated by Kaplan−Meier curves; increased HSP27 and Menin expression correlated with shorter survival of PCa patients (p = 0.001 and p < 0.0001, respectively). Accuracy in predicting aggressiveness was quantified by the Area Under the Curve (AUC) of Receiver Operating Characteristic (ROC). We demonstrated that the combination of HSP27/Menin was statistically greater than PSA; it achieved an AUC of 0.824 (95% CI, 0.730−0.918; p < 0.0001). However, HSP27/Menin/PSA combination decreased the diagnostic value with an AUC of 0.569 (95% CI, 0.428−0.710; p = 0.645). Our work suggests the potential role of HSP27/Menin as diagnostic and prognostic biomarkers.

Combinatorial targeting of a chromatin complex comprising Dot1L, menin and the tyrosine kinase BAZ1B reveals a new therapeutic vulnerability of endocrine therapy-resistant breast cancer

BACKGROUND

Targeting vulnerabilities of cancer cells by inhibiting key regulators of cell proliferation or survival represents a promising way to overcome resistance to current therapies. In breast cancer (BC), resistance to endocrine therapy results from constitutively active or aberrant estrogen receptor alpha (ERα) signaling to the genome. Targeting components of the ERα pathway in these tumors represents, therefore, a rational way toward effective new treatments. Interaction proteomics identified several proteins associated with ERα in BC cells, including epigenetic complexes controlling gene transcription comprising the scaffold protein menin and the histone methyltransferase Dot1L.

METHODS

We combined chromatin immunoprecipitation, transcriptome sequencing, siRNA-mediated gene knockdown (kd), pharmacological inhibition coupled to cellular and functional assays and interaction proteomics in antiestrogen (AE)-sensitive and AE-resistant human BC cell models to: map menin and Dot1L chromatin localization, search for their common and specific target genes, measure the effects of single or combinatorial knockdown or pharmacological inhibition of these proteins on cell proliferation and survival, and characterize their nuclear interactomes.

RESULTS

Dot1L and menin associate in MCF-7 cells chromatin, where they co-localize in a significant fraction of sites, resulting in co-regulation of genes involved, among others, in estrogen, p53, HIF1α and death receptor signaling, regulation of cell cycle and epithelial-to-mesenchymal transition. Specific inhibitors of the two factors synergize with each other for inhibition of cell proliferation of AE (tamoxifen or fulvestrant)-sensitive and AE-resistant BC cells. Menin and Dot1L interactomes share a sizeable fraction of their nuclear partners, the majority being known BC fitness genes. Interestingly, these include B-WICH and WINAC complexes that share BAZ1B, a bromodomain protein comprising a tyrosine-protein kinase domain playing a central role in chromatin remodeling and transcriptional regulation. BAZ1B kd caused significant inhibition of ERα expression, proliferation and transcriptome changes resulting in inhibition of estrogen, myc, mTOR, PI3K and AKT signaling and metabolic pathways in AE-sensitive and AE-resistant BC cells.

CONCLUSIONS

Identification of a functional interplay between ERα, Dot1L, menin and BAZ1B and the significant effects of their co-inhibition on cell proliferation and survival in cell models of endocrine therapy-resistant BC reveal a new therapeutic vulnerability of these aggressive diseases.

Astilbin ameliorates depressive-like behavior caused by postnatal immune activation through Menin-regulated astrocyte inflammation

Postnatal immune activation (PIA) can affect normal brain development and increase the risk of behavioral abnormalities in later life, including depressive-like behavior. Therefore, there is an urgent need to find safe and effective clinical medications for PIA. Recently, the protective effect of astilbin (ASB) in nervous system diseases has attracted much attention. However, the effect of ASB on neurodevelopmental diseases remains unclear. In this study, we used a lipopolysaccharide (LPS)-induced PIA mouse model and found that ASB specifically improved PIA-induced depressive-like behavior but not anxiety-like behavior in adult mice. Astrocytes play an essential role in regulating neuroinflammation, and are the most abundant cell type in the brain. In the PIA model, we found that ASB selectively inhibited astrocyte activation but not microglial activation in the cortex and hippocampus. Moreover, our results showed that ASB specifically upregulated the expression of menin protein in astrocytes and blocked the entry of P65 protein into the nucleus, thus inhibiting the secretion of IL-1β and TNF-α by astrocytes. Taken together, ASB reduced the occurrence of astrocyte-mediated neuroinflammation by targeting menin, thereby attenuating the PIA-induced depressive-like behavior. Our results reveal that ASB may be an attractive antidepressant drug and exert an antidepressant effect in PIA. In terms of drug selection, ASB may be a specific drug for patients with depressive symptoms.

Menin regulates lipid deposition in mouse hepatocytes via interacting with transcription factor FoxO1

Non-alcoholic fatty liver disease (NAFLD) is rapidly being recognized as the leading cause of chronic liver disease worldwide. Men1, encoding protein of menin, is a key causative gene of multiple endocrine neoplasia type 1 syndrome including pancreatic tumor. It is known that insulin that secretes by endocrine tissue pancreatic islets plays a critical role in hepatic metabolism. Mouse model of hemizygous deletion of Men1 was shown to have severe hepatic metabolism disorders. However, the molecular function of menin on lipid deposition in hepatocytes needs to be further studied. Transcriptome sequencing does show that expression suppression of Men1 in mouse hepatocytes widely affect signaling pathways involved in hepatic metabolism, such as fatty acid metabolism, insulin response, glucose metabolism and inflammation. Further molecular studies indicates that menin overexpression inhibits expressions of the fat synthesis genes Srebp-1c, Fas, and Acc1, the fat differentiation genes Pparγ1 and Pparγ2, and the fat transport gene Cd36, thereby inhibiting the fat accumulation in hepatocytes. The biological process of menin regulating hepatic lipid metabolism was accomplished by interacting with the transcription factor FoxO1, which is also found to be critical for lipid metabolism. Moreover, menin responds to insulin in hepatocytes and mediates its regulatory effect on hepatic metabolism. Our findings suggest that menin is a crucial mediation factor in regulating the hepatic fat deposition, suggesting it could be a potential important therapeutic target for NAFLD.

Induction of ß Cell Replication by Small Molecule-Mediated Menin Inhibition and Combined PKC Activation and TGF‑ß Inhibition as Revealed by A Refined Primary Culture Screening

OBJECTIVE

Pancreatic β cells are recognized as central players in the pathogenesis of types 1 and 2 diabetes. Efficient and robust primary culture methods are required to interrogate β cell biology and screen potential anti-diabetic therapeutics. The aim of this study was to refine monolayer culture of beta cells and to investigate potential inducers of beta cell proliferation.

MATERIALS AND METHODS

In this experimental study, we compared different culture methods to optimize conditions required for a monolayer culture of rat pancreatic islet cells in order to facilitate image analysis-based assays. We also used the refined culture method to screen a group of rationally selected candidate small molecules and their combinations to determine their potential proliferative effects on the β cells.

RESULTS

Ham's F10 medium supplemented with 2% foetal bovine serum (FBS) in the absence of any surface coating provided a superior monolayer β cell culture, while other conditions induced fibroblast-like cell growth or multilayer cell aggregation over two weeks. Evaluation of candidate small molecules showed that a menin inhibitor MI-2 and a combination of transforming growth factor-β (TGF-β) inhibitor SB481542 and protein kinase C (PKC) activator indolactam V (IndV) significantly induced replication of pancreatic β cells.

CONCLUSION

Overall, our optimized culture condition provided a convenient approach to study the cultured pancreatic islet cells and enabled us to detect the proliferative effect of menin inhibition and combined TGF-β inhibition and PKC activation, which could be considered as potential strategies for inducing β cell proliferation and regeneration.

Reduced menin expression leads to decreased ERα expression and is correlated with the occurrence of human luminal B-like and ER-negative breast cancer subtypes

Purpose

Menin, encoded by the MEN1 gene, was recently reported to be involved in breast cancers, though the underlying mechanisms remain elusive. In the current study, we sought to further determine its role in mammary cells.

Methods

Menin expression in mammary lesions from mammary-specific Men1 mutant mice was detected using immunofluorescence staining. RT-qPCR and western blot were performed to determine the role of menin in ERα expression in human breast cancer cell lines. ChIP-qPCR and reporter gene assays were carried out to dissect the action of menin on the proximal ESR1 promoter. Menin expression in female patients with breast cancer was analyzed and its correlation with breast cancer subtypes was investigated.

Results

Immunofluorescence staining revealed that early mammary neoplasia in Men1 mutant mice displayed weak ERα expression. Furthermore, MEN1 silencing led to both reduced ESR1 mRNA and ERα protein expression in MCF7 and T47D cells. To further dissect the regulation of ESR1 transcription by menin, we examined whether and in which way menin could regulate the proximal ESR1 promoter, which has not been fully explored. Using ChIP analysis and reporter gene assays covering − 2500 bp to + 2000 bp of the TSS position, we showed that the activity of the proximal ESR1 promoter was markedly reduced upon menin downregulation independently of H3K4me3 status. Importantly, by analyzing the expression of menin in 354 human breast cancers, we found that a lower expression was associated with ER-negative breast cancer (P = 0.041). Moreover, among the 294 ER-positive breast cancer samples, reduced menin expression was not only associated with larger tumors (P = 0.01) and higher SBR grades (P = 0.005) but also with the luminal B-like breast cancer subtype (P = 0.006). Consistent with our clinical data, we demonstrated that GATA3 and FOXA1, co-factors in ESR1 regulation, interact physically with menin in MCF7 cells, and MEN1 knockdown led to altered protein expression of GATA3, the latter being a known marker of the luminal A subtype, in MCF7 cells.

Conclusion

Taken together, our data provide clues to the important role of menin in ERα regulation and the formation of breast cancer subtypes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06339-9.

Targeting Chromatin Complexes in Myeloid Malignancies and Beyond: From Basic Mechanisms to Clinical Innovation

The aberrant function of chromatin regulatory networks (epigenetics) is a hallmark of cancer promoting oncogenic gene expression. A growing body of evidence suggests that the disruption of specific chromatin-associated protein complexes has therapeutic potential in malignant conditions, particularly those that are driven by aberrant chromatin modifiers. Of note, a number of enzymatic inhibitors that block the catalytic function of histone modifying enzymes have been established and entered clinical trials. Unfortunately, many of these molecules do not have potent single-agent activity. One potential explanation for this phenomenon is the fact that those drugs do not profoundly disrupt the integrity of the aberrant network of multiprotein complexes on chromatin. Recent advances in drug development have led to the establishment of novel inhibitors of protein–protein interactions as well as targeted protein degraders that may provide inroads to longstanding effort to physically disrupt oncogenic multiprotein complexes on chromatin. In this review, we summarize some of the current concepts on the role epigenetic modifiers in malignant chromatin states with a specific focus on myeloid malignancies and recent advances in early-phase clinical trials.

A novel MEN1 pathogenic variant in an Italian patient with multiple endocrine neoplasia type 1

The multiple endocrine neoplasia type 1 (MEN1) is a rare syndrome characterized by the predisposition to developing multiple endocrine and non-endocrine tumors, typically characterized by the association between parathyroid gland hyperplasia or tumors, gastroenteropancreatic tumors and pituitary adenomas. The MEN1 gene is located on the long arm of chromosome 11 (11q13) and it encodes for the protein "menin". We here reported the case of a MEN1-patient, affected by primary hyperparathyroidism, insulinoma, pituitary non-hyperfunctioning adenoma and bilateral adrenal masses, carrying a novel heterozygous pathogenic variant (c.1252_1254delGACinsAT), located in exon 9 of MEN1 gene.

Multiple endocrine neoplasia type 1 revealed by a hip pathologic fracture

Multiple endocrine neoplasia type 1 is a rare autosomal inherited syndrome that affects a variety of endocrine tissues such as the parathyroid, endocrine pancreas, and anterior pituitary. Osseous complications are often misdiagnosed. We presented a case of a 46-year-old woman with pathological fractures of the lower limb. She had a history of type 1 diabetes and galactorrhea. Laboratory examinations showed hypercalcemia and an increased level of parathyroid hormone related to hyperparathyroidism. Serum chromogranin A level was increased at 9369 ng/mL (N < 102). A somatostatin receptor scintigraphy (octreoscan) revealed pathological uptake in the gastric wall, later cave adenopathy, and liver. The diagnosis of multiple endocrine neoplasia type 1 was made based on radiological and histological findings. The patient underwent a subtotal parathyroidectomy associated with somatostatin analog treatment leading to significant improvement. A literature review was conducted by searching PubMed using these following terms: multiple endocrine neoplasia type 1, hyperparathyroidism, fracture, menin, osteoporosis. We emphasized bone involvement related to multiple endocrine neoplasia type 1 syndrome. This diagnosis should be considered when pathological fractures occur in young patients with a history of endocrine disorder. We highlighted the importance of imaging features in making the diagnosis of multiple endocrine neoplasia type 1. Early management of this disease is necessary. Treatment including parathyroidectomy and somatostatin analogs leads to bone preservation and functional improvement.

Combined inhibition of menin-MLL interaction and TGF-β signaling induces replication of human pancreatic beta cells

Both type 1 and type 2 diabetes are associated with hyperglycemia and loss of functional beta cell mass. Inducing proliferation of preexisting beta cells is an approach to increase the numbers of beta cells. In this study, we examined a panel of selected small molecules for their proliferation-inducing effects on human pancreatic beta cells. Our results demonstrated that a small molecule inhibitor of the menin-MLL interaction (MI-2) and small molecule inhibitors of TGF-β signaling (SB431542, LY2157299, or LY364947) synergistically increased ex vivo replication of human beta cells. We showed that this increased proliferation did not affect insulin production, as a pivotal indication of beta cell function. We further provided evidence which suggested that menin-MLL and TGF-β inhibition cooperated through downregulation of cell cycle inhibitors CDKN1A, CDKN1B, and CDKN2C. Our findings might provide a new option for extending the pharmacological repertoire for induction of beta cell proliferation as a potential therapeutic approach for diabetes.

Wild-type menin is rapidly degraded via the ubiquitin-proteasome pathway in a rat insulinoma cell line

Menin is encoded by multiple endocrine neoplasia type 1 (MEN1) gene, the germ line mutations of which are the main cause of pancreatic neuroendocrine tumors (PNETs). To date, a large number of frameshift, nonsense and missense mutations of MEN1 have been identified to be responsible for part of MEN1-defficient PNETs patients due to truncation or rapid degradation of menin protein. However, the stability of the wild-type (WT) menin in PNETs is totally unknown. In the present study, we observed ubiquitination of WT menin in 293T cells by transfection of ectopic WT menin and HA-ubiquitin. As expected, either endogenous or ectopic WT menin is stable in 293T cells, whereas in INS-1 cells, a rat insulinoma cell line derived from PNETs, either endogenous or ectopic WT menin is rapidly degraded through ubiquitin-proteasome pathway. Furthermore, the degradation of WT menin is more rapid in the presence of serum. Our findings suggest that in part of PNETs patients with WT MEN1, a ubiquitin-proteasome system targeting menin is untimely activated.

Menin Coordinates C/EBPβ-Mediated TGF-β Signaling for Epithelial-Mesenchymal Transition and Growth Inhibition in Pancreatic Cancer

Menin displays either tumor suppression or promotion functions in a context-dependent manner. Previously, we proposed that Menin acts as a tumor suppressor by inhibiting cell growth in pancreatic ductal adenocarcinoma (PDAC), whereas the relationship between the Menin expression and overall survival rate of PDAC patients has not been completely elucidated, indicating the complexity of Menin functions in PDAC progression. Here, we identify Menin as a promoter of epithelial-mesenchymal transition (EMT), which is largely associated with cell migration or metastasis, with modest activity in cell growth inhibition. Ectopic expression of Menin suppresses the expression of CCAAT/enhancer-binding protein beta (CEBPB) and epithelial-specific genes by histone deacetylation and further enhances the TGF-β signaling-related EMT process. We also demonstrate that CCAAT/enhancer binding protein (C/EBP) beta (C/EBPβ; encoded by CEBPB) acts downstream of Menin and TGF-β signaling for balancing growth inhibition and EMT, and C/EBPβ overexpression could restore the anti-cancer functions of Menin in pancreatic cancer by cooperatively activating CDKN2A/B genes and antagonizing EMT processes. Taken together, our results suggest that Menin functions as an oncogene for cancer metastasis upon C/EBPβ depletion or acts as a tumor suppressor by cooperation with C/EBPβ to activate CDKN2A transcription.

Disruption of the menin-MLL interaction triggers menin protein degradation via ubiquitin-proteasome pathway

Menin, a protein encoded by the MEN1 gene, suppresses cancers associated with multiple endocrine neoplasia type 1 (MEN1), but promotes the development of a subset of leukemia induced by mixed lineage leukemia (MLL)-derived fusion proteins (MLL-FPs). The crystal structure of menin indicates that it acts as a scaffold protein to bind the N-terminus of MLL via a central pocket. Small molecule menin-MLL inhibitors (MIs) bind the menin pocket to disrupt the menin/MLL interaction, resulting in suppression of MLL-FP-transformed acute myeoloid leukemia (AML). It is thought that MIs suppress the MLL-FP-induced leukemia by blocking the menin/MLL interaction and menin/MLL-induced HOX gene transcription. However, it is not clear whether MIs also affect other aspects of menin biology beyond disruption of the menin/MLL interaction. Here we show for the first time that MIs reduced menin protein levels and decreased the half-life of menin protein but have no effect on mRNA level in MLL-FP-expressing leukemia cells, and proteasome or E1 ligase inhibitor rescued the MI-induced menin degradation. Notably, the MI-induced reduction of H3K4m3 and HOXA9 expression was rescued with a proteasome inhibitor that blocks MI-induced menin protein degradation. Mechanistically, MIs promote the interaction of menin with Hsp70-associated ubiquitin ligase CHIP, resulting in increased menin ubiquitination, leading to increased menin degradation. Together, these findings uncover a novel mechanism whereby small molecule MIs increase menin degradation by triggering the Hsp70/CHIP-mediated ubiquitin-proteasome pathway that ultimately leads to the reduction in HOXA9 gene expression and leukemia suppression.

Pituitary somatolactotropes evade an oncogenic response to Ras

Distinct cell types have been shown to respond to activated Ras signaling in a cell-specific manner. In contrast to its pro-tumorigenic role in some human epithelial cancers, oncogenic Ras triggers differentiation of pheochromocytoma cells and medullary thyroid carcinoma cells. Furthermore, we have previously demonstrated that in pituitary somatolactotropes, activated Ras promotes differentiation and is not sufficient to drive tumorigenesis. These findings demonstrate that lactotrope cells have the ability to evade the tumorigenic fate that is often associated with persistent activation of Ras/ERK signaling, and suggest that there may be differential expression of inhibitory signaling molecules or negative cell cycle regulators that act as a brake to prevent the tumorigenic effects of sustained Ras signaling. Here we aim to gain further insight into the mechanisms that allow GH4T2 cells to evade an oncogenic response to Ras. We show that Ral, but likely not menin, plays a key role in directing Ras-mediated differentiation of somatolactotropes, which may allow these cells to escape the tumorigenic fate that is often associated with activated Ras signaling. We also show that dominant negative Ras expression results in reduced GH4T2 cell proliferation and transformation, but does not influence differentiation. Taken together, the data presented here begin to shed light on the mechanisms by which pituitary somatolactotropes evade an oncogenic response to persistently activated Ras signaling and suggest that the architecture of the Ras signaling cascade in some endocrine cell types may be distinct from that of cells that respond to Ras in an oncogenic manner.

Molecular Genetic Studies of Pancreatic Neuroendocrine Tumors: New Therapeutic Approaches

Pancreatic neuroendocrine tumors (PNETs) arise sporadically or as part of familial syndromes. Genetic studies of hereditary syndromes and whole exome sequencing analysis of sporadic NETs have revealed the roles of some genes involved in PNET tumorigenesis. The multiple endocrine neoplasia type 1 (MEN1) gene is most commonly mutated. Its encoded protein, menin, has roles in transcriptional regulation, genome stability, DNA repair, protein degradation, cell motility and adhesion, microRNA biogenesis, cell division, cell cycle control, and epigenetic regulation. Therapies targeting epigenetic regulation and MEN1 gene replacement have been reported to be effective in preclinical models.

Expression of p27Kip1 and p18Ink4c in human multiple endocrine neoplasia type 1-related pancreatic neuroendocrine tumors

PURPOSE

Pancreatic neuroendocrine tumors are a major manifestation of multiple endocrine neoplasia type 1 (MEN1). This tumor syndrome is caused by germline mutations in MEN1, encoding menin. Insight into pathogenesis of these tumors might lead to new biomarkers and therapeutic targets for these patients. Several lines of evidence point towards a role for p27^Kip1 and p18^Ink4c in MEN1-related tumor development in animal models for MEN1, but their contribution to human MEN1-related pancreatic neuroendocrine tumor development is not known.

METHODS

In this study, we characterized protein expression of p27^Kip1 and p18^Ink4c in human MEN1-related PanNETs by immunohistochemistry. From the nationwide DutchMEN1 Study Group database including > 90% of the Dutch MEN1 population, MEN1-patients, who underwent pancreatic surgery, were selected. A tissue micro-array was constructed with available paraffin tissue blocks, and PanNETs from 61 MEN1 patients were eligible for analysis.

RESULTS

Expression of p27^Kip1 was high in 57 (93%) PanNETs and 67% of the tumors showed low expression of p18^Ink4c (67.3%). No association was found between expression of either p27^Kip1 or p18^Ink4c and clinic-pathological characteristics.

CONCLUSIONS

These findings indicate that loss of p18^Ink4c, but not p27^Kip1, is a common event in the development of MEN1-related PanNETs. Restoration of p18^Ink4c function through CDK4/6 inhibitors could be a therapeutic option for MEN1-related PanNETs.

Inhibition of microRNA-24 increases liver fibrosis by enhanced menin expression in Mdr2-/- mice

BACKGROUND

Liver transplantation remains the primary treatment for primary sclerosing cholangitis (PSC). Mdr2-/- mice provide a reliable in vivo model of PSC and develop characteristic biliary inflammation and fibrosis. We tested the hypothesis that the tumor suppressor protein menin is implicated in the progression of liver fibrosis and that menin expression can be regulated in the liver via microRNA-24 (miR-24).

MATERIALS AND METHODS

Menin expression was measured in human PSC and Mdr2-/- mice. Twelve-week-old FVB/NJ wild-type (WT) and Mdr2-/- mice were treated with miR-24 Vivo-Morpholino to knockdown miR-24 expression levels. Liver fibrosis was evaluated by Sirius Red staining and quantitative polymerase chain reaction (qPCR) for genes associated with liver fibrosis, such as fibronectin 1, collagen type 1 alpha 1, transforming growth factor-β1 (TGF-β1), and α-smooth muscle actin. Studies were also performed in vitro using immortalized murine cholangiocyte lines treated with miR-24 hairpin inhibitor and mimic.

RESULTS

Menin gene expression was increased in Mdr2-/- mice and late-stage human PSC samples. Treatment of FVB/NJ WT and Mdr2-/- mice with miR-24 Vivo-Morpholino increased menin expression, which correlated with increased expression of fibrosis genes. In vitro, inhibition of miR-24 also significantly increased the expression of fibrosis genes.

CONCLUSIONS

Inhibition of miR-24 increases menin and TGF-β1 expression, subsequently increasing hepatic fibrosis in FVB/NJ WT and Mdr2-/- mice. Modulation of the menin/miR-24 axis may provide novel targeted therapies to slow the progression of hepatic fibrosis into cirrhosis in PSC patients by altering TGF-β1 expression.

Direct interaction of menin leads to ubiquitin-proteasomal degradation of β-catenin

Menin, encoded by the multiple endocrine neoplasia type 1 (MEN1) gene, is a tumor suppressor and transcription regulator. Menin interacts with various proteins as a scaffold protein and is proposed to play important roles in multiple physiological and pathological processes by controlling gene expression, proliferation, and apoptosis. The mechanisms underlying menin's suppression of tumorigenesis are largely elusive. In this study, we showed that menin was essential for the regulation of canonical Wnt/β-catenin signaling in cultured cells. The C-terminal domain of menin was able to directly interact with and promote ubiquitin-mediated degradation of β-catenin. We further revealed that overexpression of menin down-regulated the transcriptional activity of β-catenin and target gene expression. Moreover, menin efficiently inhibited β-catenin protein levels, transcriptional activity, and proliferation of human renal carcinoma cells with an activated β-catenin pathway. Taken together, our results provide novel molecular insights into the tumor suppressor activity of menin, which is partly mediated by proteasomal degradation of β-catenin and inhibition of Wnt/β-catenin signaling.

MEN1 mutations and potentially MEN1-targeting miRNAs are responsible for menin deficiency in sporadic and MEN1 syndrome-associated primary hyperparathyroidism

Inherited, germline mutations of menin-coding MEN1 gene cause multiple endocrine neoplasia type 1 (MEN1), while somatic MEN1 mutations are the sole main driver mutations in sporadic primary hyperparathyroidism (PHPT), suggesting that menin deficiency has a central role in the pathogenesis of PHPT. MiRNAs are small, noncoding RNAs posttranscriptionally regulating gene expression. Our aim was to investigate both the role of MEN1 mutations and potentially MEN1-targeting miRNAs as the underlying cause of menin deficiency in MEN1-associated and sporadic PHPT tissues. Fifty six PHPT tissues, including 16 MEN1-associated tissues, were evaluated. Diagnosis of MEN1 syndrome was based on identification of germline MEN1 mutations. In silico target prediction was used to identify miRNAs potentially targeting MEN1. Menin expression was determined by immunohistochemistry while expression of miRNAs was analyzed by quantitative real-time PCR. Sporadic PHPT tissues were subjected to somatic MEN1 mutation analysis as well. Lack of nuclear menin was identified in all MEN1-associated and in 28% of sporadic PHPT tissues. Somatic MEN1 mutations were found in 25% of sporadic PHPTs. The sensitivity and specificity of menin immunohistochemistry to detect a MEN1 mutation were 86 and 87%, respectively. Expression levels of hsa-miR-24 and hsa-miR-28 were higher in sporadic compared to MEN1-associated PHPT tissues; however, no difference in miRNA levels occurred between menin-positive and menin-negative PHPT tissues. Menin deficiency is the consequence of a MEN1 mutation in most menin-negative PHPT tissues. Elevated expression of hsa-miR-24 and hsa-miR-28 mark the first epigenetic changes observed between sporadic and MEN1-associated PHPT.

Genetics of multiple endocrine neoplasia type 1 syndrome: what's new and what's old

Despite its identification in 1997, the functions of the MEN1 gene-the main gene underlying multiple endocrine neoplasia type 1 syndrome-are not yet fully understood. In addition, unlike the RET-MEN2 causative gene-no hot-spot mutational areas or genotype-phenotype correlations have been identified. More than 1,300 MEN1 gene mutations have been reported and are mostly "private" (family specific). Even when mutations are shared at an intra- or inter-familial level, the spectrum of clinical presentation is highly variable, even in identical twins. Despite these inherent limitations for genetic counseling, identifying MEN1 mutations in individual carriers offers them the opportunity to have lifelong clinical surveillance schemes aimed at revealing MEN1-associated tumors and lesions, dictates the timing and scope of surgical procedures, and facilitates specific mutation analysis of relatives to define presymptomatic carriers.

Lung adenocarcinoma and adrenocortical carcinoma in a patient with multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder caused by heterozygous germline mutations in the tumor suppressor gene MEN1, which encodes a nuclear protein, menin. MEN1 is characterized by the combined occurrence of tumors involving the pituitary gland, pancreatic islets, and parathyroid glands. Additionally, patients with MEN1 often exhibit adrenal tumors. Although most MEN1-associated tumors are benign, malignant lesions arising in these endocrine organs have been reported. Additionally, malignant diseases of non-endocrine organs concomitant with MEN1 have also been reported. Here, we report a rare case of a MEN1 patient who exhibited adrenocortical carcinoma (ACC) and lung adenocarcinoma (LAC). A 53-year-old Japanese woman was diagnosed with genetically proven MEN1 that initially manifested as parathyroid, pancreatic, and adrenal tumors. During the course of the disease, she developed LAC harboring the epidermal growth factor receptor gene mutations and cortisol-secreting ACC. Both tumors were surgically resected. The tumor cells were immunohistochemically negative for menin. Studies have suggested a causative link between MEN1 gene mutations and ACC, and menin expression may decrease in MEN1-related ACCs. In contrast, there are few reports suggesting a specific role of MEN1 gene mutations in LAC. Menin is often inactivated in the LACs of patients without MEN1. Thus, our patient's ACC probably occurred as part of MEN1, whereas the latter had no evident etiological association with her LAC. This case demonstrates the need for physicians to consider the potential development of malignant diseases originating from both endocrine and non-endocrine organs in MEN1 patients.

Design and synthesis of benzylpiperidine inhibitors targeting the menin-MLL1 interface

Menin is an essential oncogenic cofactor for mixed lineage leukemia (MLL)-mediated leukemogenesis, functioning through its direct interaction with MLL1 protein. Therefore, targeting the menin-MLL1 protein-protein interface represents a promising strategy to block MLL-mediated leukemogenesis. On the basis of co-crystal structure analysis, starting from thienopyrimidine chemotype, we have investigated the detailed structure-activity relationship of the piperazinyl-dihydrothiazole moiety. Several compounds were found with potent inhibitory activity against menin and better activities in cell-based experiments than MI-2-2. Molecular docking analysis revealed a less explored subpocket, which could be used for the design of new menin-MLL1 inhibitors.

Aberrant Menin expression is an early event in pancreatic neuroendocrine tumorigenesis

Pancreatic neuroendocrine tumors (PanNETs) are the second most common pancreatic malignancy and cause significant morbidity and mortality. Neuroendocrine microadenomas have been proposed as a potential precursor lesion for sporadic PanNETs. In this study, we applied telomere-specific fluorescent in situ hybridization (FISH) to a series of well-characterized sporadic neuroendocrine microadenomas and investigated the prevalence of alterations in known PanNET driver genes (MEN1 and ATRX/DAXX) in these same tumors using immunohistochemistry for the encoded proteins. We identified aberrant Menin expression in 14 of 19 (74%) microadenomas, suggesting that alterations in Menin, at least a subset of which was likely due to somatic mutation, are early events in pancreatic neuroendocrine tumorigenesis. In contrast, none of the microadenomas met criteria for the alternative lengthening of telomeres phenotype (ALT) based on telomere FISH, a phenotype that is strongly correlated to ATRX or DAXX mutations. Two of 13 microadenomas (15%) were noted to have very rare abnormal bright telomere foci on FISH, suggestive of early ALT, but these lesions did not show loss of ATRX or DAXX protein expression by immunohistochemistry. Overall, these data suggest that loss of Menin is an early event in pancreatic neuroendocrine tumorigenesis and that ATRX/DAXX loss and ALT are relatively late events.

Animal models of multiple endocrine neoplasia

Multiple endocrine neoplasia (MEN) syndromes are autosomal dominant diseases with high penetrance characterized by proliferative lesions (usually hyperplasia or adenoma) arising in at least two endocrine tissues. Four different MEN syndromes have been so far identified: MEN type 1 (MEN1), MEN2A (also referred to as MEN2), MEN2B (or MEN3) and MEN4, which have slightly varying tumor spectra and are caused by mutations in different genes. MEN1 associates with loss-of-function mutations in the MEN1 gene encoding the tumor suppressor menin. The MEN2A and MEN2B syndromes are due to activating mutations in the proto-oncogene RET (Rearranged in Transfection) and are characterized by different phenotypic features of the affected patients. MEN4 was the most recent addition to the family of the MEN syndromes. It was discovered less than 10 years ago thanks to studies of a rat strain that spontaneously develops multiple endocrine tumors (named MENX). These studies identified an inactivating mutation in the Cdkn1b gene, encoding the putative tumor suppressor p27, as the causative mutation of the rat syndrome. Subsequently, germline mutations in the human ortholog CDKN1B were also found in a subset of patients with a MEN-like phenotype and this led to the identification of MEN4. Small animal models have been instrumental in understanding important biochemical, physiological and pathological processes of cancer onset and spread in intact living organisms. Moreover, they have provided us with insight into gene function(s) and molecular mechanisms of disease progression. We here review the currently available animal models of MEN syndromes and their impact on the elucidation of the pathophysiology of these diseases, with a special focus on the rat MENX syndrome that we have been characterizing.

Interplay between menin and Dnmt1 reversibly regulates pancreatic cancer cell growth downstream of the Hedgehog signaling pathway

Menin, the product of the Men1 gene, which is frequently mutated in pancreatic neuroendocrine tumors, acts as a chromatin-remodeling factor to modulate the transcription of cell cycle regulators by interacting with histone modification factors. However, the function of menin and its underlying mechanisms in pancreatic ductal adenocarcinoma remain unknown. Here, we found that menin inhibited pancreatic cancer cell growth in vitro and in vivo and that its expression was gradually lost during pancreatic carcinogenesis. Menin overexpression significantly activated the expression of the cyclin-dependent kinase (CDK) inhibitors p18 and p27, accompanied with a decrease in DNA methylation levels of p18 and p27 promoters. Mechanistically, we found that interaction of menin with DNA methyltransferase 1 (Dnmt1) competitively pulled down Dnmt1 from p18 and p27 promoters, leading to the downregulation of DNA methylation levels. Moreover, menin expression was suppressed by Dnmt1 downstream of the Hedgehog signaling pathway, and menin overexpression strongly antagonized the promotion effect of hedgehog signaling on pancreatic cancer cell proliferation. Taken together, the interaction between menin and Dnmt1 reversibly regulates pancreatic cancer cell growth downstream of Hedgehog pathways with complex mutual modulation networks, suggesting that the Hedgehog/Dnmt1/menin axis is a potential molecular target for pancreatic cancer therapy.

Tumor suppressor Menin acts as a corepressor of LXRα to inhibit hepatic lipogenesis

Menin, encoded by the MEN1 gene, was initially identified as a tumor suppressor for endocrine neoplasia. Our previous report showed that Menin enhances PPARα transactivity preventing triglyceride accumulation in the liver. Here, we further explore the role of Menin in liver steatosis. Transient transfection assays demonstrate that Menin inhibits the transcriptional activity of nuclear receptor liver X receptor α (LXRα). Accordingly, Menin overexpression results in reduced expression of LXRα target genes, such as lipogenic enzymes including SREBP-1c, FASN and SCD-1. Co-immunoprecipitation assays revealed physical interaction between Menin and LXRα. Collectively, our data suggest that Menin acts as a novel corepressor of LXRα and functions as a negative regulator of hepatic lipogenesis.

Progress towards small molecule menin-mixed lineage leukemia (MLL) interaction inhibitors with in vivo utility

A series of substituted hydroxymethyl piperidine small molecule inhibitors of the protein-protein interaction between menin and mixed lineage leukemia 1 (MLL1) are described. Initial members of the series showed good inhibitory disruption of the menin-MLL1 interaction but demonstrated poor physicochemical and DMPK properties. Utilizing a structure-guided and iterative optimization approach key substituents were optimized leading to inhibitors with cell-based activity, improved in vitro DMPK parameters, and improved half-lives in rodent PK studies leading to MLPCN probe ML399. Ancillary off-target activity remains a parameter for further optimization.

Osteoblast menin regulates bone mass in vivo

Menin, the product of the multiple endocrine neoplasia type 1 (Men1) tumor suppressor gene, mediates the cell proliferation and differentiation actions of transforming growth factor-β (TGF-β) ligand family members. In vitro, menin modulates osteoblastogenesis and osteoblast differentiation promoted and sustained by bone morphogenetic protein-2 (BMP-2) and TGF-β, respectively. To examine the in vivo function of menin in bone, we conditionally inactivated Men1 in mature osteoblasts by crossing osteocalcin (OC)-Cre mice with floxed Men1 (Men1(f/f)) mice to generate mice lacking menin in differentiating osteoblasts (OC-Cre;Men1(f/f) mice). These mice displayed significant reduction in bone mineral density, trabecular bone volume, and cortical bone thickness compared with control littermates. Osteoblast and osteoclast number as well as mineral apposition rate were significantly reduced, whereas osteocyte number was increased. Primary calvarial osteoblasts proliferated more quickly but had deficient mineral apposition and alkaline phosphatase activity. Although the mRNA expression of osteoblast marker and cyclin-dependent kinase inhibitor genes were all reduced, that of cyclin-dependent kinase, osteocyte marker, and pro-apoptotic genes were increased in isolated Men1 knock-out osteoblasts compared with controls. In contrast to the knock-out mice, transgenic mice overexpressing a human menin cDNA in osteoblasts driven by the 2.3-kb Col1a1 promoter, showed a gain of bone mass relative to control littermates. Osteoblast number and mineral apposition rate were significantly increased in the Col1a1-Menin-Tg mice. Therefore, osteoblast menin plays a key role in bone development, remodeling, and maintenance.

Menin-mediated regulation of miRNA biogenesis uncovers the IRS2 pathway as a target for regulating pancreatic beta cells

Menin, a protein encoded by the MEN1 gene, is mutated in patients with multiple endocrine neoplasia type 1 (MEN1). Menin acts as a tumor suppressor in endocrine organs while it is also required for transformation of a subgroup of leukemia. The recently solved crystal structure of menin with different binding partners reveals that menin is a key scaffold protein that cross-talks with various partners, including transcription factors, to regulate gene transcription. Our recent findings unravel a previously undiscovered mechanism for menin-mediated control of gene expression via processing of certain microRNA's, thus adding to the plethora of ways in which menin regulates gene expression. By interacting with ARS2, an RNA binding protein, menin facilitates the processing of pri-let 7a and pri-miR155 to pre-let 7a and pre-miR155 respectively. Consistently, excision of the Men1 gene results in upregulation of IRS2, a let-7a target. As IRS2 is known to mediate both insulin signaling and insulin-induced cell proliferation, and let-7a targets include oncogenes like RAS and HMGA2, a deeper understanding of the menin-ARS2 complex in regulating miRNA biogenesis will yield further insights into the pathogenesis of the MEN1 syndrome and other menin-associated malignancies.

The role of tumor suppressor menin in IL-6 regulation in mouse islet tumor cells

Menin is a gene product of multiple endocrine neoplasia type1 (Men1), an inherited familial cancer syndrome characterized by tumors of endocrine tissues. To gain insight about how menin performs an endocrine cell-specific tumor suppressor function, we investigated the possibility that menin was integrated in a cancer-associated inflammatory pathway in a cell type-specific manner. Here, we showed that the expression of IL-6, a proinflammatory cytokine, was specifically elevated in mouse islet tumor cells upon depletion of menin and Men(-/-) MEF cells, but not in hepatocellular carcinoma cells. Histone H3 lysine (K) 9 methylation, but not H3 K27 or K4 methylation, was involved in menin-dependent IL-6 regulation. Menin occupied the IL-6 promoter and recruited SUV39H1 to induce H3 K9 methylation. Our findings provide a molecular insight that menin-dependent induction of H3 K9 methylation in the cancer-associated interleukin gene might be linked to preventing endocrine-specific tumorigenesis.

p27 Loss Is Associated with Poor Prognosis in Gastroenteropancreatic Neuroendocrine Tumors

Purpose

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a heterogeneous disease group originating from the neuroendocrine cells. Identification of prognostic markers, related to neuroendocrine tissue-selective tumorigenesis, is necessary to find therapeutic targets.

Materials and Methods

A total of 327 patients with GEP-NETs were included in this study; there were 49 gastric, 29 duodenal, 49 pancreatic, 12 hepatobiliary, 33 appendiceal, 5 proximal colon, and 150 distal colon cases. We performed immunostaining with the tissue microarray method for menin, p27, and p18.

Results

We observed negative staining for menin, p27, and p18 in 34%, 21%, and 56% of GEP-NETs, respectively. The loss of p27, but not menin, was positively correlated with the grade of Ki-67. Menin–/p27–, menin–/p27+, menin+/p27–, and menin+/p27+ phenotype groups included 13%, 22%, 8%, and 57% of patients, respectively. A dichotomized comparison showed that menin– or p27– tumors were significantly associated with foregut and midgut localizations, high World Health Organization (WHO) grade, lymph node metastasis, and more advanced stage as compared to menin+/p27+ patients. Kaplan-Meier analysis for the overall survival showed that p27 loss was significantly associated with decreased survival. Multivariate analysis showed that p27 loss is an independent factor for poor overall survival.

Conclusion

Our results revealed that the loss of p27 is associated with poor prognosis and the menin-p27 pathway is important in the tumorigenesis of GEP-NETs.

Cucurbitacin-E inhibits multiple cancer cells proliferation through attenuation of Wnt/β-catenin signaling

Recent studies suggest that the use of cucurbitacins could inhibit cancer cell progression. In the current study, the authors analyzed the effect of cucurbitacin-E (CuE) in cancer cells using A549, Hep3B, and SW480 cells. The authors found that CuE inhibited cell proliferation and modulated the expression of cell cycle regulators in these cells. Moreover, the authors found that CuE inhibited Wnt/β-catenin signaling activation through upregulation of tumor suppressor Menin. Indeed, ablation of Menin using small interfering RNA (siRNA) oligos attenuated the antiproliferative roles of CuE. Taken together, the results of this study provide a novel mechanism that may contribute to the antineoplastic effects of CuE in cancer cells.

Menin is required for optimal processing of the microRNA let-7a

Multiple endocrine neoplasia type I (MEN1) is an inherited syndrome that includes susceptibility to pancreatic islet hyperplasia. This syndrome results from mutations in the MEN1 gene, which encodes menin protein. Menin interacts with several transcription factors, including JunD, and inhibits their activities. However, the precise mechanism by which menin suppresses gene expression is not well understood. Here, we show that menin interacts with arsenite-resistant protein 2 (ARS2), a component of the nuclear RNA CAP-binding complex that is crucial for biogenesis of certain miRNAs including let-7a. The levels of primary-let-7a (pri-let-7a) are not affected by menin; however, the levels of mature let-7a are substantially decreased upon Men1 excision. Let-7a targets, including Insr and Irs2, pro-proliferative genes that are crucial for insulin-mediated signaling, are up-regulated in Men1-excised cells. Inhibition of let-7a using anti-miRNA in wild type cells is sufficient to enhance the expression of insulin receptor substrate 2 (IRS2) to levels observed in Men1-excised cells. Depletion of menin does not affect the expression of Drosha and CBP80, but substantially impairs the processing of pri-miRNA to pre-miRNA. Ars2 knockdown decreased let-7a processing in menin-expressing cells but had little impact on let-7a levels in menin-excised cells. As IRS2 is known to mediate insulin signaling and insulin/mitogen-induced cell proliferation, these findings collectively unravel a novel mechanism whereby menin suppresses cell proliferation, at least partly by promoting the processing of certain miRNAs, including let-7a, leading to suppression of Irs2 expression and insulin signaling.

Menin regulates spinal glutamate-GABA balance through GAD65 contributing to neuropathic pain

BACKGROUND

Our previous work found that tumor suppressor menin potentiates spinal synaptic plasticity in the context of peripheral nerve injury-induced neuropathic hypersensitivity, but the underlying molecular mechanisms are not clear. We hereby assessed the role of menin in regulating the spinal balance between glutamate and GABA and its contribution to the pathological condition of nerve injury-induced hypersensitivity.

METHODS

In spared nerve injury induced C57BL/6 mice, mechanical withdrawal threshold was measured with von Frey filaments after intrathecal administration of small interfering RNA (siRNA) of MEN1 or/and subcutaneous histone deacetylase (HDAC) inhibitors to control the level of glutamic acid decarboxylase 65 (GAD65). Immunoblotting and high-performance liquid chromatography were used to detect the level of protein expression and spinal glutamate and GABA, respectively.

RESULTS

Genetic knockdown of spinal menin alleviated nerve injury evoked mechanical hypersensitivity, which was strongly associated with the alteration of the spinal level of GAD65 that resulted in an imbalance of glutamate/GABA ratio from the baseline ratio of 5.8 ± 0.9 (×10(-4)) to the peak value of 58.6 ± 11.8 (×10(-4)) at the day 14 after SNI (p < 0.001), which was reversed by MEN1 siRNA to 14.7 ± 2.1 (×10(-4)) at the day 14 after nerve injury (p < 0.01). In further, selective inhibitors of HDACs considerably reversed the ratio of spinal glutamate and GABA, and also alleviated the mechanical withdrawal threshold markedly.

CONCLUSION

Our findings provide mechanistic insight into the contribution of the upregulated spinal menin to peripheral nerve injury induced neuropathic hypersensitivity by regulating glutamate-GABA balance through deactivating GAD65.

GSK-3β protein phosphorylates and stabilizes HLXB9 protein in insulinoma cells to form a targetable mechanism of controlling insulinoma cell proliferation

Insulinomas (pancreatic islet β cell tumors) are the most common type of functioning pancreatic neuroendocrine tumors that occur sporadically or as a part of the MEN1 syndrome that is caused by germ line mutations in MEN1. Tissue-specific tumor predisposition from germ line mutations in ubiquitously expressed genes such as MEN1 could occur because of functional consequences on tissue-specific factors. We previously reported the proapoptotic β cell differentiation factor HLXB9 as a downstream target of menin (encoded by MEN1). Here we show that GSK-3β inactivates the proapoptotic activity of HLXB9 by phosphorylating HLXB9 at Ser-78/Ser-80 (pHLXB9). Although HLXB9 is found in the nucleus and cytoplasm, pHLXB9 is predominantly nuclear. Both pHLXB9 and active GSK-3β are elevated in β cells with menin knockdown, in MEN1-associated β cell tumors (insulinomas), and also in human sporadic insulinomas. Pharmacologic inhibition of GSK-3β blocked cell proliferation in three different rodent insulinoma cell lines by arresting the cells in G2/M phase and caused apoptosis. Taken together, these data suggest that the combination of GSK-3β and pHLXB9 forms a therapeutically targetable mechanism of insulinoma pathogenesis. Our results reveal that GSK-3β and pHLXB9 can serve as novel targets for insulinoma treatment and have implications for understanding the pathways associated with β cell proliferation.

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.