Orphan quality control shapes network dynamics and gene expression.

All eukaryotes require intricate protein networks to translate developmental signals into accurate cell fate decisions. Mutations that disturb interactions between network components often result in disease, but how the composition and dynamics of complex networks are established remains poorly understood. Here, we identify the E3 ligase UBR5 as a signaling hub that helps degrade unpaired subunits of multiple transcriptional regulators that act within a network centered on the c-Myc oncoprotein. Biochemical and structural analyses show that UBR5 binds motifs that only become available upon complex dissociation. By rapidly turning over unpaired transcription factor subunits, UBR5 establishes dynamic interactions between transcriptional regulators that allow cells to effectively execute gene expression while remaining receptive to environmental signals. We conclude that orphan quality control plays an essential role in establishing dynamic protein networks, which may explain the conserved need for protein degradation during transcription and offers opportunities to modulate gene expression in disease.

Mcrs1 regulates G2/M transition and spindle assembly during mouse oocyte meiosis.

Microspherule protein 1 (Mcrs1) is a component of the nonspecific lethal (NSL) complex and the chromatin remodeling INO80 complex, which participates in transcriptional regulation during mitosis. Here, we investigate the roles of Mcrs1 during female meiosis in mice. We demonstrate that Mcrs1 is a novel regulator of the meiotic G2/M transition and spindle assembly in mouse oocytes. Mcrs1 is present in the nucleus and associates with spindle poles and chromosomes of oocytes during meiosis I. Depletion of Mcrs1 alters HDAC2-mediated H4K16ac, H3K4me2, and H3K9me2 levels in nonsurrounded nucleolus (NSN)-type oocytes, and reduces CDK1 activity and cyclin B1 accumulation, leading to G2/M transition delay. Furthermore, Mcrs1 depletion results in abnormal spindle assembly due to reduced Aurora kinase (Aurka and Aurkc) and Kif2A activities, suggesting that Mcrs1 also plays a transcription-independent role in regulation of metaphase I oocytes. Taken together, our results demonstrate that the transcription factor Mcrs1 has important roles in cell cycle regulation and spindle assembly in mouse oocyte meiosis.

Histone acetylation of bile acid transporter genes plays a critical role in cirrhosis.

BACKGROUND & AIMS: Owing to the lack of genetic animal models that adequately recreate key clinical characteristics of cirrhosis, the molecular pathogenesis of cirrhosis has been poorly characterized, and treatments remain limited. Hence, we aimed to better elucidate the pathological mechanisms of cirrhosis using a novel murine model. METHODS: We report on the first murine genetic model mimicking human cirrhosis induced by hepatocyte-specific elimination of microspherule protein 1 (MCRS1), a member of non-specific lethal (NSL) and INO80 chromatin-modifier complexes. Using this genetic tool with other mouse models, cell culture and human samples, combined with quantitative proteomics, single nuclei/cell RNA sequencing and chromatin immunoprecipitation assays, we investigated mechanisms of cirrhosis. RESULTS: MCRS1 loss in mouse hepatocytes modulates the expression of bile acid (BA) transporters - with a pronounced downregulation of Na+-taurocholate cotransporting polypeptide (NTCP) - concentrating BAs in sinusoids and thereby activating hepatic stellate cells (HSCs) via the farnesoid X receptor (FXR), which is predominantly expressed in human and mouse HSCs. Consistently, re-expression of NTCP in mice reduces cirrhosis, and genetic ablation of FXR in HSCs suppresses fibrotic marks in mice and in vitro cell culture. Mechanistically, deletion of a putative SANT domain from MCRS1 evicts histone deacetylase 1 from its histone H3 anchoring sites, increasing histone acetylation of BA transporter genes, modulating their expression and perturbing BA flow. Accordingly, human cirrhosis displays decreased nuclear MCRS1 and NTCP expression. CONCLUSIONS: Our data reveal a previously unrecognized function of MCRS1 as a critical histone acetylation regulator, maintaining gene expression and liver homeostasis. MCRS1 loss induces acetylation of BA transporter genes, perturbation of BA flow, and consequently, FXR activation in HSCs. This axis represents a central and universal signaling event in cirrhosis, which has significant implications for cirrhosis treatment. LAY SUMMARY: By genetic ablation of MCRS1 in mouse hepatocytes, we generate the first genetic mouse model of cirrhosis that recapitulates human features. Herein, we demonstrate that the activation of the bile acid/FXR axis in liver fibroblasts is key in cirrhosis development.

miR-186 modulates hepatocellular carcinoma cell proliferation and mobility via targeting MCRS1-mediated Wnt/ß-catenin signaling.

Previous studies have revealed that miR-186 is involved in the pathogenesis of many malignancies. However, the role of miR-186 in hepatocellular carcinoma (HCC) carcinogenesis and its detailed mechanism are poorly understood. This study was to investigate the function of miR-186 in modulating HCC cell proliferation, cell cycle, migration, and invasion. We found that miR-186 was decreased in HCC tissues and cell lines. Loss-of-function experiments showed that reduction of miR-186 dramatically enhanced tumor cell proliferation and metastasis. Besides, miR-186 also participated in the modulation of the cell cycle. In addition, luciferase reporter assays and Western blot analysis showed that MCRS1 was a novel target of miR-186 in HCC cells. Notably, upregulation of miR-186 suppressed the nuclear ß-catenin accumulation and blocked the activation of Wnt/ß-catenin signaling in HCC cells. Forced MCRS1 expression abrogated the inhibitory effect of miR-186 on cell growth, metastasis and Wnt/ß-catenin signaling in HCC cells. Our findings may provide new insight into the pathogenesis of HCC and miR-186/ MCRS1 might function as new therapeutic targets for HCC.

The molecular characteristics and functional roles of microspherule protein 1 (MCRS1) in gene expression, cell proliferation, and organismic development.

Accurate spatial and temporal regulation of cell cycle progression is essential for cell proliferation and organismic development. This review demonstrates the role of microspherule protein 58kD, commonly known as MCRS1, as a key cell cycle regulator of higher eukaryotic organisms. We discuss the isoforms and functional domains of MCRS1 as well as their subcellular localization at specific stages of the cell cycle. These molecular characteristics reveal MCRS1's dynamic regulatory role in gene expression, genome stability, cell proliferation, and organismic development. Furthermore, we discuss the molecular details of its seemingly opposite, tumor-suppressive or tumor-promoting, role in different types of cancer.

MCRS1 Expression Regulates Tumor Activity and Affects Survival Probability of Patients with Gastric Cancer.

Gastric cancer is the fifth most common cancer worldwide and the third most common cause of cancer-related deaths. Surgery remains the first-choice treatment. Chemotherapy is considered in the middle and advanced stages, but has limited success. Microspherule protein 1 (MCRS1, also known as MSP58) is a protein originally identified in the nucleus and cytoplasm that is involved in the cell cycle. High expression of MCRS1 increases tumor growth, invasiveness, and metastasis. The mechanistic relationships between MCSR1 and proliferation, apoptosis, angiogenesis, and epithelial-mesenchymal transition (EMT) remain to be elucidated. We clarified these relationships using immunostaining of tumor tissues and normal tissues from patients with gastric cancer. High MCRS1 expression in gastric cancer positively correlated with Ki-67, Caspase3, CD31, Fibronectin, pAKT, and pAMPK. The hazard ratio of high MCRS1 expression was 2.44 times that of low MCRS1 expression, negatively impacting patient survival.

Effects of MCRS1 on proliferation, migration, invasion, and epithelial mesenchymal transition of gastric cancer cells by interacting with Pkmyt1 protein kinase.

Microspherule protein 1(MCRS1) is known to be an oncogene in several tumors. However, recent studies have shown that MCRS1 inhibits lymphatic metastasis in gastric cancer (GC) patients by inhibiting telomerase activity. Protein kinase, membrane associated tyrosine/threonine 1(Pkmyt1), a member of the WEE1 family, has been found to interact with MCRS1 by yeast two-hybrid assay; however, how these two proteins interact in GC is still unclear. Hence, this study aimed to investigate the effect of MCRS1 interaction with Pkmyt1 on GC cell proliferation, migration, and invasion. Initially, we observed increased expression of MCRS1 in GC SGC-7901 cells and decreased expression in GC BGC-823 cells. Hence, we down-regulated MCRS1 expression in SGC-7901 cells and up-regulated it in BGC-823 cells. Our results showed that overexpression of MCRS1 inhibits the growth, invasion and migration of GC cells, while downregulation of MCRS1 promotes the growth, invasion and migration of GC cells. When MK1775, an inhibitor of WEE1 kinase, was added after downregulation of MCRS1, phenotypic recovery effects were observed. Overexpression of MCRS1 also inhibited the expression of Pkmyt1 and vice versa. This indicated that there might be a possible interaction between MCRS1 and Pkmyt1. Furthermore, immunoprecipitation assay revealed the interaction between MCRS1 and Pkmyt1 in virto, and immunofluorescence experiments showed that the two proteins were co-localized in the cytoplasm. In conclusion, our study confirmed the specific tumor suppressive activity of MCRS1 in GC proliferation, invasion and migration and suggested that it might inhibit the progression of GC through its interaction with Pkmyt1.

mTORC1 Inactivation Promotes Colitis-Induced Colorectal Cancer but Protects from APC Loss-Dependent Tumorigenesis.

Dietary habits that can induce inflammatory bowel disease (IBD) are major colorectal cancer (CRC) risk factors, but mechanisms linking nutrients, IBD, and CRC are unknown. Using human data and mouse models, we show that mTORC1 inactivation-induced chromosomal instability impairs intestinal crypt proliferation and regeneration, CDK4/6 dependently. This triggers interleukin (IL)-6-associated reparative inflammation, inducing crypt hyper-proliferation, wound healing, and CRC. Blocking IL-6 signaling or reactivating mTORC1 reduces inflammation-induced CRC, so mTORC1 activation suppresses tumorigenesis in IBD. Conversely, mTORC1 inactivation is beneficial in APC loss-dependent CRC. Thus, IL-6 blockers or protein-rich-diet-linked mTORC1 activation may prevent IBD-associated CRC. However, abolishing mTORC1 can mitigate CRC in predisposed patients with APC mutations. Our work reveals mTORC1 oncogenic and tumor-suppressive roles in intestinal epithelium and avenues to optimized and personalized therapeutic regimens for CRC.

Transport to Rhebpress activity.

The small GTPases from the rat sarcoma (Ras) superfamily are a heterogeneous group of proteins of about 21 kDa that act as molecular switches, modulating cell signaling pathways and controlling diverse cellular processes. They are active when bound to guanosine triphosphate (GTP) and inactive when bound to guanosine diphosphate (GDP). Ras homolog enriched in brain (Rheb) is a member of the Ras GTPase superfamily and a key activator of the mammalian/mechanistic target of rapamycin complex 1 (mTORC1). We recently determined that microspherule protein 1 (MCRS1) maintains Rheb at lysosomal surfaces in an amino acid-dependent manner. MCRS1 depletion promotes the formation of the GDP-bound form of Rheb, which is then delocalized from the lysosomal platform and transported to endocytic recycling vesicles, leading to mTORC1 inactivation. During this delocalization process, Rheb-GDP remains farnesylated and associated with cellular endomembranes. These findings provide new insights into the regulation of small GTPases, whose activity depends on both their GTP/GDP switch state and their capacity to move between different cellular membrane-bound compartments. Dynamic spatial transport between compartments makes it possible to alter the proximity of small GTPases to their activatory sites depending on the prevailing physiological and cellular conditions.

Aurora-A regulates MCRS1 function during mitosis.

The mitotic spindle is made of microtubules (MTs) nucleated through different pathways involving the centrosomes, the chromosomes or the walls of pre-existing MTs. MCRS1 is a RanGTP target that specifically associates with the chromosome-driven MTs protecting them from MT depolymerases. MCRS1 is also needed for the control of kinetochore fiber (K-fiber) MT minus-ends dynamics in metaphase. Here, we investigated the regulation of MCRS1 activity in M-phase. We show that MCRS1 is phosphorylated by the Aurora-A kinase in mitosis on Ser35/36. Although this phosphorylation has no role on MCRS1 localization to chromosomal MTs and K-fiber minus-ends, we show that it regulates MCRS1 activity in mitosis. We conclude that Aurora-A activity is particularly important in the tuning of K-fiber minus-ends dynamics in mitosis.

Stabilization of MCRS1 by BAP1 prevents chromosome instability in renal cell carcinoma.

Characterization of the exome and genome of carcinoma (ccRCC) by next-generation sequencing identified numerous genetic alternations. BRCA1-associated protein-1 (BAP1) was identified as one of the most frequently mutated genes in ccRCC, suggesting that BAP1 is a potential key driver for ccRCC cancer initiation and progression. However, how BAP1 mutations contribute to ccRCC remains to be elucidated. BAP1 is a nuclear de-ubiquitinating enzyme and cleaves the ubiquitin chain from the substrates. Here, we identified MCRS1 as a bona fide substrate for BAP1. MCRS1 is a component of the centrosome proteins, and plays an essential role in spindle assembly. BAP1 binds to MCRS1 and stabilizes MCRS1 by de-ubiquitination. BAP1 contributes to chromosome stability partially via MCRS1. A positive correlation was identified between BAP1 and MCRS1 expression in ccRCC tissues. Both BAP1 loss and MCRS1 down-regulation in ccRCC were associated with adverse clinicopathological features. This study revealed a novel mechanism for BAP1 involved in MCRS1 stability regulation, and provided insight in understanding the relationship between BAP1 mutations and chromosome instability in ccRCC.