Mammalian STE20-like Protein Kinase Research Articles

STK3 kinase activation inhibits tumor proliferation through FOXO1-TP53INP1/P21 pathway in esophageal squamous cell carcinoma.

Esophageal squamous cell carcinoma (ESCC) is an aggressive disease with a poor prognosis, caused by the inactivation of critical cell growth regulators that lead to uncontrolled proliferation and increased malignancy. Although Serine/Threonine Kinase 3 (STK3), also known as Mammalian STE20-like protein kinase 2 (MST2), is a highly conserved kinase of the Hippo pathway, plays a critical role in immunomodulation, organ development, cellular differentiation, and cancer suppression, its phenotype and function in ESCC require further investigation. In this study, we report for the first time on the role of STK3 kinase and its activation condition in ESCC, as well as the mechanism and mediators of kinase activation. In this study, we investigated the expression and clinical significance of STK3 in ESCC. We first used bioinformatics databases and immunohistochemistry to analyze STK3 expression in the ESCC patient cohort and conducted survival analysis. In vivo, we conducted a tumorigenicity assay using nude mouse models to demonstrate the phenotypes of STK3 kinase. In vitro, we conducted Western blot analysis, qPCR analysis, CO-IP, and immunofluorescence (IF) staining analysis to detect molecule expression, interaction, and distribution. We measured proliferation, migration, and apoptosis abilities in ESCC cells in the experimental groups using CCK-8 and transwell assays, flow cytometry, and EdU staining. We used RNA-seq to identify genes that were differentially expressed in ESCC cells with silenced STK3 or FOXO1. We demonstrated the regulatory relationship of the TP53INP1/P21 gene medicated by the STK3-FOXO1 axis using Western blotting and ChIP in vitro. We demonstrate high STK3 expression in ESCC tissue and cell lines compared to esophageal epithelium. Cellular ROS induces STK3 autophosphorylation in ESCC cells, resulting in upregulated p-STK3/4. STK3 activation inhibits ESCC cell proliferation and migration by triggering apoptosis and suppressing the cell cycle. STK3 kinase activation phosphorylates FOXO1Ser212, promoting nuclear translocation, enhancing transcriptional activity, and upregulating TP53INP1 and P21. We also investigated TP53INP1 and P21's phenotypic effects in ESCC, finding that their knockdown significantly increases tumor proliferation, highlighting their crucial role in ESCC tumorigenesis. STK3 kinase has a high expression level in ESCC and can be activated by cellular ROS, inhibiting cell proliferation and migration. Additionally, STK3 activation-mediated FOXO1 regulates ESCC cell apoptosis and cell cycle arrest by targeting TP53INP1/P21. Our research underscores the anti-tumor function of STK3 in ESCC and elucidates the mechanism underlying its anti-tumor effect on ESCC.

New Insights into the Roles of the Hippo Signaling Pathway in Stem Cell Biology

: A highly conserved kinase cascade, including mammalian STE20-like protein kinases (MSTs), large tumor suppressors (LATSs), and downstream transcription coactivators containing YES-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are involved in the Hippo signaling pathway. As two critical transcriptional coactivators, TAZ and YAP are adversely regulated by the Hippo signaling pathway. They lead to the induction of organ regeneration and the expression of cell growth and division-promoting genes through binding to transcription factors, especially TEA domain transcription factors (TEADs). Previous studies highlight the role of the Hippo pathway in organ size control, homeostasis, cell proliferation, and tumor development. Research has shown this pathway's vital role in cancer stem cell biology, including self-renewal and drug resistance. Improper activation of YAP and TAZ through the Hippo pathway dysregulation or its increased expression can accelerate tumorigenesis. Thus, pharmacological inhibition of YAP and TAZ is suggested as a promising approach in the treatment of tumors with high YAP/TAZ activity.

Low MST1/2 and negative LATS1/2 expressions are associated with poor prognosis of colorectal cancers

Mammalian STe20-like protein kinase 1/2 (MST1/2) and large tumor suppressor homolog 1/2 (LATS1/2) are the core components of the tumor-suppressive Hippo pathway. Dysregulation of this pathway is associated with the progression and metastasis of various cancers. However, MST1/2 and LATS1/2 expressions have not been systematically evaluated in colorectal cancers. We evaluated the clinicopathologic correlation and prognostic significance of MST1/2 and LATS1/2 immunohistochemical expressions in 327 colorectal cancer patients. Low MST1/2 expression, identified in 235 (71.9 %) cases, was significantly associated with poor differentiation (P = 0.018) and large size (P < 0.001) of the tumor. Negative LATS1/2 expression, identified in 226 (69.1 %) cases, was significantly correlated with low MST1/2 expression (P = 0.044). Low MST1/2 and negative LATS1/2 expressions were significantly associated with poor overall survivals (P = 0.015 and P = 0.038, respectively). Furthermore, the combined MST1/2lowLATS1/2negative expression group showed significantly worse overall survival than other groups (P = 0.003), and considered as an independent poor prognostic factor for colorectal cancer patients (hazard ratio = 1.720; 95 % confidence interval, 1.143–2.588; P = 0.009). Low MST1/2 and negative LATS1/2 expressions may serve as prognostic indicators in patients with colorectal cancer.

YAP promotes AP-1 expression in tubular epithelial cells in the kidney.

Chronic kidney disease (CKD) is a major health problem. Kidney fibrosis is a hallmark and final common pathway of CKD. The Hippo/yes-associated protein (YAP) pathway regulates organ size, inflammation, and tumorigenesis. Our previous study demonstrated tubular YAP activation by tubule-specific double knockout of mammalian STE20-like protein kinase 1/2 (Mst1/2) induced CKD in mice, but the underlying mechanisms remain to be fully elucidated. Activator protein (AP)-1 activation was found to promote tubular atrophy and tubulointerstitial fibrosis. Therefore, we studied whether YAP regulates AP-1 expression in the kidney. We found that expression of various AP-1 components was induced in kidneys subjected to unilateral ureteric obstruction and in Mst1/2 double knockout kidneys, and these inductions were blocked by deletion of Yap in tubular cells, with Fosl1 being most affected compared with other AP-1 genes. Inhibition of Yap also most highly suppressed Fosl1 expression among AP-1 genes in HK-2 and IMCD3 renal tubular cells. YAP bound to the Fosl1 promoter and promoted Fosl1 promoter-luciferase activity. Our results suggest that YAP controls AP-1 expression and that Fosl1 is the primary target of YAP in renal tubular cells.NEW & NOTEWORTHY Yes-associated protein (YAP) activation leads to tubular injury, renal inflammation, and fibrosis, but the underlying mechanisms are not fully understood. We now provide genetic evidence that YAP promotes activator protein-1 expression and that Fosl1 is the primary target of YAP in renal tubular cells.

Genetic variants in Mammalian STE20-like protein kinase 2 were associated with risk of NSCL/P

AimMammalian STE20-like protein kinase 2 (MST2) plays an important role in apoptosis and the development of many disorders. Here, we aim to explore if genetic variants in MST2 are associated with the risk of non-syndromic cleft lip with or without palate (NSCL/P). Materials and methodsThe association study was performed in a two-stage study of 1,069 cases and 1,724 controls to evaluate the association between genetic variants in the MST2 and NSCL/P risk. The potential function of the candidate single nucleotide polymorphism (SNP) was predicted using HaploReg, RegulomeDB, and public craniofacial histone chromatin immunoprecipitation sequencing (ChIP-seq) data. Haploview was used to perform the haplotype of risk alleles. The expression quantitative trait loci (eQTL) effect was assessed using the Genotype-Tissue Expression (GTEx) project. Gene expression in mouse embryo tissue was performed using data downloaded from GSE67985. The potential role of candidate gene in the development of NSCL/P was assessed by correlation and enrichment analysis. ResultsAmong SNPs in MST2, rs2922070 C allele (Pmeta = 2.93E-04) and rs6988087 T allele (Pmeta = 1.57E-03) were linked with significantly increased risk of NSCL/P. Rs2922070, rs6988087 and their high linkage disequilibrium (LD) SNPs constituted a risk haplotype of NSCL/P. Individuals carrying 3–4 risk alleles had an elevated risk of NSCL/P compared to those who carried less risk alleles (P = 2.00E-04). The eQTL analysis revealed a significant association between these two variants and MST2 in muscle tissue of the body. The MST2 expressed during mouse craniofacial development and over-expressed in the human orbicularis oris muscle (OOM) of NSCL/P patients compared to controls. MST2 was involved in the development of NSCL/P by regulating the mRNA surveillance pathway, the MAPK signaling pathway, the neurotrophin signaling pathway, the FoxO signaling pathway and the VEGF signaling pathway. ConclusionMST2 was associated with the development of NSCL/P.

MST4: A Potential Oncogene and Therapeutic Target in Breast Cancer.

The mammalian STE 20-like protein kinase 4 (MST4) gene is highly expressed in several cancer types, but little is known about the role of MST4 in breast cancer, and the function of MST4 during epithelial-mesenchymal transition (EMT) has not been fully elucidated. Here we report that overexpression of MST4 in breast cancer results in enhanced cell growth, migration, and invasion, whereas inhibition of MST4 expression significantly attenuates these properties. Further study shows that MST4 promotes EMT by activating Akt and its downstream signaling molecules such as E-cadherin/N-cadherin, Snail, and Slug. MST4 also activates AKT and its downstream pro-survival pathway. Furthermore, by analyzing breast cancer patient tissue microarray and silicon datasets, we found that MST4 expression is much higher in breast tumor tissue compared to normal tissue, and significantly correlates with cancer stage, lymph node metastasis and a poor overall survival rate (p < 0.05). Taken together, our findings demonstrate the oncogenic potential of MST4 in breast cancer, highlighting its role in cancer cell proliferation, migration/invasion, survival, and EMT, suggesting a possibility that MST4 may serve as a novel therapeutic target for breast cancer.

Neratinib as a Potential Therapeutic for Mutant RAS and Osimertinib-Resistant Tumours

Neratinib was developed as an irreversible catalytic inhibitor of ERBB2, which also acts to inhibit ERBB1 and ERBB4. Neratinib is U.S. Food and Drug Administration (FDA)-approved as a neo-adjuvant therapy for use in HER2+ breast cancer. More recently, chemical biology analyses and the authors’ own bench work have demonstrated that neratinib has additional targets, which open up the possibility of using the drug in cell types that either lack ERBB receptor family expression or who rely on survival signalling downstream of growth factor receptors. Neratinib rapidly disrupted mutant RAS nanoclustering, which was followed by mutant rat sarcoma virus proteins translocating via LC3-associated phagocytosis into the cytosol where they were degraded by macroautophagy. Neratinib catalytically inhibited the MAP4K mammalian STE20-like protein kinase 4 and also caused its degradation via macroautophagy. This resulted in ezrin dephosphorylation and the plasma membrane becoming flaccid. Neratinib disrupted the nanoclustering of RAC1, which was associated with dephosphorylation of PAK1 and Merlin, and with increased phosphorylation of the Merlin binding partners large tumour suppressor kinase 1/2, YAP, and TAZ. YAP and TAZ exited the nucleus. Neratinib retained its anti-tumour efficacy against NSCLC cells made resistant to either afatinib or to osimertinib. Collectively, these findings argue that the possibilities for the further development of neratinib as cancer therapeutic in malignancies that do not express or over-express members of the ERBB receptor family are potentially wide-ranging.

Effect of Inactivation of Mst1 and Mst2 in the Mouse Adrenal Cortex.

Recent conditional knockout of core components of the Hippo signaling pathway in the adrenal gland of mice has demonstrated that this pathway must be tightly regulated to ensure proper development and maintenance of the adrenal cortex. We report herein that the most upstream kinases of the pathway, the mammalian STE20-like protein kinases 1 and 2 (MST1and MST2, respectively), are expressed in the mouse adrenal cortex with MST2 expression being restricted to the zona glomerulosa (zG). To further explore the role of Hippo signaling in adrenocortical cells, we conditionally deleted Mst1/2 in steroidogenic cells using an Nr5a1-cre strain (Mst1 flox/flox ; Mst2 flox/flox ; Nr5a1-cre). Our results show that the loss of MST1/2 leads to the premature and progressive accumulation of subcapsular GATA4+, WT1+ adrenal gonadal primordium (AGP)-like progenitor cells starting at 2 months of age without affecting aldosterone and corticosterone secretion. To help us understand this phenotype, microarray analyses were performed on adrenal glands from 2-month-old mutant and control mice. Gene expression analyses revealed that loss of Mst1/2 leads to the overexpression of known downstream target genes (Ajuba, Aqp1, Fn1, Ibsp, Igf1, Igfbp2, Mmp2, Thbs1) of the main effector of Hippo signaling, YAP; and underexpression of genes (Agtr1b, Ecgr4, Hsd3b6, Nr0b1, Tesc, Vsnl1) that are normally specifically expressed in the zG or overexpressed in the zG compared to the zona fasciculata (zF). Together, these results suggest that MST1/2 regulates Hippo signaling activity in the adrenal cortex and that these two kinases are also involved in the fine tuning of zG cell function or differentiation.

Combinatorial targeting of Hippo-STRIPAK and PARP elicits synthetic lethality in gastrointestinal cancers.

The striatin-interacting phosphatase and kinase (STRIPAK) complexes integrate extracellular stimuli that result in intracellular activities. Previously, we discovered that STRIPAK is a key machinery responsible for loss of the Hippo tumor suppressor signal in cancer. Here, we identified the Hippo-STRIPAK complex as an essential player in the control of DNA double-stranded break (DSB) repair and genomic stability. Specifically, we found that the mammalian STE20-like protein kinases 1 and 2 (MST1/2), independent of classical Hippo signaling, directly phosphorylated zinc finger MYND type–containing 8 (ZMYND8) and hence resulted in the suppression of DNA repair in the nucleus. In response to genotoxic stress, the cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway was determined to relay nuclear DNA damage signals to the dynamic assembly of Hippo-STRIPAK via TANK-binding kinase 1–induced (TBK1-induced) structural stabilization of the suppressor of IKBKE 1– sarcolemma membrane–associated protein (SIKE1-SLMAP) arm. As such, we found that STRIPAK-mediated MST1/2 inactivation increased the DSB repair capacity of cancer cells and endowed these cells with resistance to radio- and chemotherapy and poly(ADP-ribose)polymerase (PARP) inhibition. Importantly, targeting the STRIPAK assembly with each of 3 distinct peptide inhibitors efficiently recovered the kinase activity of MST1/2 to suppress DNA repair and resensitize cancer cells to PARP inhibitors in both animal- and patient-derived tumor models. Overall, our findings not only uncover what we believe to be a previously unrecognized role for STRIPAK in modulating DSB repair but also provide translational implications of cotargeting STRIPAK and PARP for a new type of synthetic lethality anticancer therapy.

Identification of NUAK1/2 Regulators in the Hippo Signaling Pathway

The Hippo signaling pathway plays a central role in regulating cell proliferation, differentiation, and tissue size. In response to various upstream regulators, the mammalian STE20‐like protein kinase 1/2 (MST1/2) and large tumor suppressor kinase 1/2 (LATS1/2) phosphorylate Yes‐associated protein (YAP) and transcriptional co‐activator with PDZ‐binding motif (TAZ) to promote their cytoplasmic retention and degradation. Unphosphorylated YAP/TAZ translocate into the nucleus and interact with several transcription factors to regulate gene expression that drives cell growth and migration. Dysregulation of the Hippo pathway causes tissue overgrowth and tumorigenesis and elevated YAP/TAZ levels or activities are positively correlated with progression of almost all solid cancers. The NUAK family kinase 1/2 (NUAK1/2) are members of the AMP‐activated protein kinase‐related kinase family. Our lab showed that NUAK2 negatively regulates the Hippo pathway by preventing LATS‐mediated YAP/TAZ phosphorylation and cytoplasmic sequestration. Moreover, this work showed that loss of NUAK2 attenuates in vivo mammary tumor growth. However, how NUAK1/2 are regulated is poorly understood.Here, we will undertake screens in cancer cell lines to identify upstream and downstream NUAK1/2 regulators and partners. Since, abrogation of NUAK expression blocks cell growth in a context‐dependent manner, my current efforts are being directed towards generating cell lines expressing inducible NUAK1/2 shRNAs. Independent clones have been selected and validated for their knockdown efficiencies and effects on YAP/TAZ downstream target gene expression. Once validated, the selected lines will be subjected to genome‐wide CRISPR screens. We hypothesize that the screens will identify components that enhance or attenuate the effect of NUAKs and will reveal any differential regulators and partners for NUAK1/2. Discovering novel cancer‐relevant NUAK regulators will enhance our understanding of the tumor promoting roles of NUAKs and provide insights into how to target these kinases for better therapeutic outcomes.

Activation of YAP1 by STK25 contributes to the progression of hepatocellular carcinoma

A pathogenic role of serine/threonine protein kinase 25 (STK25) has been observed in several chronic liver diseases. However, whether STK25 participates in hepatocellular carcinoma (HCC) remains unexplored. The current work aimed to explore the role and mechanism of STK25 in HCC. A high STK25 level was found in HCC tissue, which was associated with reduced overall survival. HCC cells with STK25 silencing displayed a marked decrease in proliferative and invasive ability, but were highly sensitive to apoptosis induced by the chemotherapy drug sorafenib. Reciprocally, HCC cells with forced expression of STK25 displayed the opposite effects. Further data unveiled that STK25 silencing restrained the activation of Yes-associated protein 1 (YAP1) associated with regulation of mammalian STE20-like protein kinase 1/2 (MST1/2). Forced expression of constitutively active YAP1 abolished STK25 silencing-induced antitumor effects, while repression of YAP1 reversed STK25 upregulation-induced protumor effects. Additionally, HCC cells with STK25 silencing exhibited reduced tumorigenic potential in vivo. Collectively, the results show that STK25 exerts a protumor function in HCC by enhancing YAP1 activation via regulation of MST1/2. These findings propose STK25 as a viable target for the development of anti-HCC therapy.

A Global Phosphorylation Atlas of Proteins Within Pathological Site of Rotator Cuff Tendinopathy.

Rotator cuff tendinopathy (RCT) is the most common cause of shoulder pain, therefore posing an important clinical problem. Understanding the mechanism and biochemical changes of RCT would be of crucial importance and pave the path to targeting novel and effective therapeutic strategies in translational perspectives and clinical practices. Phosphorylation, as one of the most important and well-studied post-translational modifications, is tightly associated with protein activity and protein functional regulation. Here in this study, we generated a global protein phosphorylation atlas within the pathological site of human RCT patients. By using Tandem Mass Tag (TMT) labeling combined with mass spectrometry, an average of 7,741 phosphorylation sites (p-sites) and 3,026 proteins were identified. Compared with their normal counterparts, 1,668 p-sites in 706 proteins were identified as upregulated, while 73 p-sites in 57 proteins were downregulated. GO enrichment analyses have shown that majority of proteins with upregulated p-sites functioned in neutrophil-mediated immunity whereas downregulated p-sites are mainly involved in muscle development. Furthermore, pathway analysis identified NF-κB–related TNF signaling pathway and protein kinase C alpha type (PKCα)–related Wnt signaling pathway were associated with RCT pathology. At last, a weighted kinase-site phosphorylation network was built to identify potentially core kinase, from which serine/threonine-protein kinase 39 (STLK3) and mammalian STE20-like protein kinase 1 (MST1) were proposed to be positively correlated with the activation of Wnt pathway.

RNF6 promotes the migration and invasion of breast cancer by promoting the ubiquitination and degradation of MST1.

Ring finger protein 6 (RNF6), a member of E3 ubiquitin ligases, plays a potential role as a tumour promoter in numerous carcinomas. However, the role and expression of RNF6 in breast cancer (BC) remains to be elucidated. The present study showed that RNF6 upregulation was detected in BC tissues and was associated with short survival in patients with BC. Multivariate analysis also revealed that RNF6 overexpression is an independent predictor for poor outcome of patients with BC. Furthermore, migration and metastasis assay indicated that RNF6 silencing significantly inhibited the invasion and migration of BC cells in vivo and in vitro, and RNF6 suppression decreased YES-associated protein (YAP) expression. RNF6 promoted the metastatic ability of BC cells via YAP. Mechanistically, RNF6 interacts with mammalian STE20-like protein kinase 1 (MST1), a key factor that regulates YAP, and promoted its ubiquitination and degradation. Additionally, RNF6 regulated YAP signalling by promoting ubiquitination and degradation of MST1 in BC. Taken together, these data may highlight a role of RNF6 in BC, which could serve as a valuable prognostic indicator and potential therapeutic target for patients with BC.

G protein-coupled estrogen receptor stimulates human trophoblast cell invasion via YAP-mediated ANGPTL4 expression

Insufficient invasion of trophoblast cells into the uterine decidua is associated with preeclampsia (PE). G protein-coupled estrogen receptor (GPER) is a membrane estrogen receptor involved in non-genomic estrogen signaling. GPER is expressed in human trophoblast cells and downregulated GPER levels are noted in PE. However, to date, the role of GPER in trophoblast cells remains largely unknown. Here, we applied RNA sequencing (RNA-seq) to HTR-8/SVneo human trophoblast cells in response to G1, an agonist of GPER, and identified angiopoietin-like 4 (ANGPTL4) as a target gene of GPER. Treatment of trophoblast cells with G1 or 17β-estradiol (E2) activated Yes-associated protein (YAP), the major downstream effector of the Hippo pathway, via GPER but in a mammalian STE20-like protein kinase 1 (MST1)-independent manner. Using pharmacological inhibitors as well as loss- and gain-of-function approaches, our results revealed that YAP activation was required for GPER-stimulated ANGPTL4 expression. Transwell invasion assays demonstrated that activation of GPER-induced ANGPTL4 promoted cell invasion. In addition, the expression levels of GPER, YAP, and ANGPTL4 were downregulated in the placenta of patients with PE. Our findings reveal a mechanism by which GPER exerts its stimulatory effect on human trophoblast cell invasion by upregulating YAP-mediated ANGPTL4 expression.

Tea polyphenols alleviate hydrogen peroxide-induced oxidative stress damage through the Mst/Nrf2 axis and the Keap1/Nrf2/HO-1 pathway in murine RAW264.7 cells.

Tea polyphenols (TPs) are the major bioactive extract from green tea that have been extensively reported to prevent and treat oxidative stress damage. In previous studies, TPs have been demonstrated to protect cells against oxidative injury induced by hydrogen peroxide (H2O2). However, the underlying mechanism remains unclear. The aim of the current study was to investigate whether the protective and regulatory effects of TPs on oxidative stress damage were dependent on the mammalian STE20-like protein kinase (Mst)/nuclear factor (erythroid-derived 2)-like 2 (Nrf2) axis and the Kelch-like ECH-associated protein 1 (Keap1)/Nrf2/heme oxygenase 1 (HO-1) pathway in RAW264.7 cells, a murine macrophage cell line. Maintaining a certain range of intracellular reactive oxygen species (ROS) levels is critical to basic cellular activities, while excessive ROS generation can override the antioxidant capacity of the cell and result in oxidative stress damage. The inhibition of ROS generation offers an effective target for preventing oxidative damage. The results of the present study revealed that pretreatment with TPs inhibited the production of intracellular ROS and protected RAW264.7 cells from H2O2-induced oxidative damage. TPs was also demonstrated to attenuate the production of nitric oxide and malondialdehyde and increase the levels of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase). In addition, following TPs treatment, alterations in Mst1/2 at the mRNA and protein level inhibited the production of ROS and promoted the self-regulation of antioxidation. TPs-induced Keap1 gene downregulation also increased the expression of Nrf2 and HO-1. Collectively, the results of the present study demonstrated that TPs provided protection against H2O2-induced oxidative injury in RAW264.7 cells.

Macrophage MST1/2 Disruption Impairs Post-Infarction Cardiac Repair via LTB4.

[Figure: see text].

LINC00941 promotes glycolysis in pancreatic cancer by modulating the Hippo pathway

Pancreatic ductal adenocarcinoma (PDAC) is one of most lethal cancers and is projected to be the second leading cause of cancer deaths in the United States by 2030. The lack of effective treatment and increased incidence in PDAC encourage a deeper knowledge of PDAC progression. By analyzing a long noncoding RNA (lncRNA) dataset, we found that increased LINC00941 expression led to poor outcomes in PDAC patients. Furthermore, in vitro and in vivo experiments revealed that LINC00941 promoted PDAC cancer cell growth by enhancing aerobic glycolysis. Mechanistically, LINC00941 was found to interact with mammalian STE20-like protein kinase 1 (MST1), which facilitated the protein phosphatase 2A (PP2A)-mediated dephosphorylation of MST1, resulting in Hippo pathway activation and consequently, enhanced glycolysis in PDAC. These results suggest that LINC00941 plays a key role in regulating PDAC tumorigenesis, potentially highlighting novel avenues for PDAC therapy.

Mdm2-Mediated Downmodulation of GRK2 Restricts Centrosome Separation for Proper Chromosome Congression.

The timing of centrosome separation and the distance moved apart influence the formation of the bipolar spindle, affecting chromosome stability. Epidermal growth factor receptor (EGFR) signaling induces early centrosome separation through downstream G protein-coupled receptor kinase GRK2, which phosphorylates the Hippo pathway component MST2 (Mammalian STE20-like protein kinase 2), in turn allowing NIMA kinase Nek2A activation for centrosomal linker disassembly. However, the mechanisms that counterbalance centrosome disjunction and separation remain poorly understood. We unveil that timely degradation of GRK2 by the E3 ligase Mdm2 limits centrosome separation in the G2. Both knockout expression and catalytic inhibition of Mdm2 result in GRK2 accumulation and enhanced centrosome separation before mitosis onset. Phosphorylation of GRK2 on residue S670 enables a complex pattern of non-K48-linked polyubiquitin chains assembled by Mdm2, which correlate with kinase protein degradation. Remarkably, GRK2-S670A protein fails to phosphorylate MST2 despite overcoming Mdm2-dependent degradation, which results in defective centrosome separation, shorter spindles, and abnormal chromosome congression. Conversely, extra levels of wild-type kinase in the G2 cause increased inter-centrosome distances with longer spindles, also converging in congression issues. Our findings show that the signals enabling activity of the GRK2/MST2/Nek2A axis for separation also switches on Mdm2 degradation of GRK2 to ensure accurate centrosome dynamics and proper mitotic spindle functionality.

MST1 inhibits the progression of breast cancer by regulating theHippo signaling pathway and may serve as a prognostic biomarker.

Breast cancer (BCa) is the most common malignancy threatening the health of women worldwide, and the incidence rate has significantly increased in the last 10 years. Mammalian STE20-like protein kinase 1 (MST1) is involved in the development of various types of malignant tumor. The present study aimed to investigate the role of MST1 in BCa and its potential involvement in the poor prognosis of patients with BCa. Reverse transcription-quantitative PCR and immunohistochemistry were used to analyze the expression levels of MST1 in BCa, and the clinicopathological characteristics and prognosis of patients with BCa were further analyzed by statistical analysis. MST1 was overexpressed in BCa cell lines (MCF-7, MDA-MB-231 and SKBR3). Cell Counting Kit-8, 5-ethynyl-2′-deoxyuridine and flow cytometry assays were used to analyze cell proliferation and apoptosis, respectively, and a wound healing assay was used to analyze cell migration. The results of the present study revealed that the downregulated expression levels of MST1 in BCa were closely associated with the poor prognosis of patients, and MST1 may be an independent risk factor for BCa. The overexpression of MST1 significantly inhibited the proliferation and migration, and promoted the apoptosis of BCa cells. In addition, the overexpression of MST1 significantly activated the Hippo signaling pathway. Treatment with XMU-MP-1 downregulated the expression levels of MST1 and partially reversed the inhibitory effects of MST1 on proliferation, migration and apoptosis-related proteins, and inhibited the Hippo signaling pathway. In conclusion, the results of the present study suggested that MST1 expression levels may be downregulated in BCa and closely associated with tumor size and clinical stage, as well as the poor prognosis of affected patients. Furthermore, MST1 may inhibit the progression of BCa by targeting the Hippo signaling pathway.

MST3 Involvement in Na+ and K+ Homeostasis with Increasing Dietary Potassium Intake.

K+ loading inhibits NKCC2 (Na-K-Cl cotransporter) and NCC (Na-Cl cotransporter) in the early distal tubules, resulting in Na+ delivery to the late distal convoluted tubules (DCTs). In the DCTs, Na+ entry through ENaC (epithelial Na channel) drives K+ secretion through ROMK (renal outer medullary potassium channel). WNK4 (with-no-lysine 4) regulates the NCC/NKCC2 through SAPK (Ste20-related proline-alanine-rich kinase)/OSR1 (oxidative stress responsive). K+ loading increases intracellular Cl−, which binds to the WNK4, thereby inhibiting autophosphorylation and downstream signals. Acute K+ loading-deactivated NCC was not observed in Cl−-insensitive WNK4 mice, indicating that WNK4 was involved in K+ loading-inhibited NCC activity. However, chronic K+ loading deactivated NCC in Cl−-insensitive WNK4 mice, indicating that other mechanisms may be involved. We previously reported that mammalian Ste20-like protein kinase 3 (MST3/STK24) was expressed mainly in the medullary TAL (thick ascending tubule) and at lower levels in the DCTs. MST3−/− mice exhibited higher ENaC activity, causing hypernatremia and hypertension. To investigate MST3 function in maintaining Na+/K+ homeostasis in kidneys, mice were fed diets containing various concentrations of Na+ and K+. The 2% KCl diets induced less MST3 expression in MST3−/− mice than that in wild-type (WT) mice. The MST3−/− mice had higher WNK4, NKCC2-S130 phosphorylation, and ENaC expression, resulting in lower urinary Na+ and K+ excretion than those of WT mice. Lower urinary Na+ excretion was associated with elevated plasma [Na+] and hypertension. These results suggest that MST3 maintains Na+/K+ homeostasis in response to K+ loading by regulation of WNK4 expression and NKCC2 and ENaC activity.