Germinal Center Kinase Research Articles

Nik‐related kinase is targeted for proteasomal degradation by the chaperone‐dependent ubiquitin ligase CHIP

Nik-related kinase (Nrk) is a member of the germinal center kinase IV family and suppresses Akt signaling. Invivo, Nrk prevents placental hyperplasia and breast cancer formation. Here, we show that Nrk is regulated by the chaperone-dependent ubiquitin ligase carboxyl terminus of heat-shock protein (Hsp)70-interacting protein (CHIP). Immunoprecipitation and liquid chromatography-tandem mass spectrometry analysis reveal that Nrk preferentially interacts with CHIP and Hsp70/90 family proteins. Nrk protein levels are decreased by CHIP overexpression and increased by siRNA-mediated CHIP knockdown. Our results indicate that Nrk is ubiquitinated by CHIP in a chaperone-dependent manner, resulting in its proteasomal degradation. CHIP targets a fraction of Nrk molecules that have lost the ability to regulate Akt signaling. We conclude that CHIP plays an important role in regulating Nrk protein levels.

Knockdown of serine/threonine-protein kinase 24 promotes tumorigenesis and myeloid-derived suppressor cell expansion in an orthotopic immunocompetent gastric cancer animal model.

A higher incidence of gastric cancer has been found in East Asia compared to the incidence in other regions. Gastric cancer patients have a poor prognosis due to distant metastasis and advanced cancer stages. Tumor escape pathways include the expansion of the immunosuppressive myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. We have successfully established an orthotopic immunocompetent gastric cancer model in C57BL/6 mice. The cell line is named M12 and was deposited at the Bioresource Collection and Research Center of Taiwan on Sep. 13, 2016 (Patent No. I604054). The orthotopic animal model of gastric cancer has similar biological characteristics as human gastric cancer. Serine/threonine-protein kinase 24 (STK24) is a member of the germinal center kinase (GCK)-III family. GCKs participate in cancer and immunological disorders. The effects of STK24 in gastric cancer are less well understood. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 technology was used to induce a STK24 genetic knockout at the genomic DNA level in tumor cells. The knockdown of the STK24 gene increased the tumor growth in an orthotopic model of gastric cancer. The STK24 gene silencing in tumors induced the expansion of CD11b+Ly6C+ cells and F4/80+ macrophages in vivo. To our knowledge, we have developed the first orthotopic transplantable model of gastric cancer in syngeneic inbred mice. Our results further indicate that STK24 is important for immune regulation during the tumorigenesis of gastric cancer.

Hippo Kinases MST1/2 Regulate Immune Cell Functions in Cancer, Infection, and Autoimmune Diseases.

Mammalian STE20-like protein kinases (MST), including MST1, MST2, MST3, and MST4, belong to the germinal center kinase (GCK) family. Kinase MST1/2 is an important component of the Hippo pathway in regulating cell proliferation, tissue homeostasis, and organ development. Recent studies have shown that Hippo kinase MST1/2 plays a crucial role in immune-associated diseases, which has attracted extensive attention of researchers. This review summarizes recent research on Hippo kinases MST1/2 in regulating the function of immune cells in innate and adaptive immune systems, and also includes its regulatory role and significance in cancer, infection, and autoimmune diseases.

Dissection of the Role of CCM Genes in Tubulogenesis Using the Drosophila Tracheal System as a Model.

Embryos deficient for an essential gene may show complex phenotypes that reflect pleiotropic functions and non-cell-autonomous requirements for the encoded protein. The generation of mosaic animals, where most cells are wild type, but a few cells are mutant, is a powerful tool permitting the detailed analysis of the cell autonomous function of a gene, in a particular cell type, at cellular and subcellular resolutions. Here we apply this method to the analysis of the Cerebral Cavernous Malformations 3 (CCM3) pathway in Drosophila.The conserved CCM3 protein functions together with its binding partner, Germinal Center Kinase III (Wheezy/GckIII in Drosophila, MST3, STK24, and STK25 in human) in the regulation of tube morphogenesis (Bergametti et al. Am J Hum Genet. 76:42-51, 2005; Fidalgo et al. J Cell Sci. 123:1274-1284, 2010; Guclu et al. Neurosurgery. 57:1008-1013, 2005; Lant et al. Nat Commun. 6:6449, 2015; Song et al. Dev Cell. 25:507-519, 2013; Ceccarelli et al. J Biol Chem. 286:25056-25064, 2011; Rehain-Bell et al. Curr Biol. 27:860-867, 2017; Xu et al. Structure. 21:1059-1066, 2013; Zhang et al. Front Biosci. 17:2295-2305, 2012; Zhang et al. Dev Cell. 27:215-226, 2013; Zheng et al. J Clin Invest. 120:2795-2804, 2010). The Drosophila proteins play a role in the regulation of tube shape in the tracheal (respiratory) system, analogous to the role of the human proteins in the vascular system. To understand the cellular basis for tube dilation defects caused by loss of pathway function, we describe techniques for the generation and analysis of positively marked homozygous mutant GckIII tracheal cells, coupled with an "open book" preparation that can be subjected to immunofluorescent analysis. Dozens of mutant tracheal cells are generated per mosaic animal, and neighboring heterozygous cells in the same animal serve as ideal internal controls.

Gck Kinase Activity Is Critical for RAS Mutated Myeloma - a Potential Treatment Approach for Targeting Specific Mutations

Introduction: Next-generation sequencing revealed frequent mutations of the RAS/mitogen-activated protein kinase (MAPK) pathway, with mutations in NRAS, KRAS or BRAF in up to 50% of newly diagnosed MM patients1. The majority of the NRAS, KRAS and BRAF mutations occur in hotspots causing constitutive activation of the corresponding pathways2. Given the upstream activator role of Germinal Center Kinase (GCK) in the MAPK pathway, GCK might be an attractive therapeutic target in MM. Indeed, we recently discovered the critical role of GCK, also named mitogen-activated protein kinase kinase kinase kinase 2 (MAP4K2), in MM cell survival and growth. Methods and Results: Our data show that GCK is higher expressed in RAS mutated MM cells compared to the wild type (WT) RAS MM cells. Silencing of GCK in RASmut MM cells (MM.1S and RPMI-8226) by using an inducible Tet-on-shGCK significantly decreased MM cell proliferation and induced cell death (Figure 1). In contrast, knockdown of GCK in RASwt MM cell lines (LP1 and U266) induced only modest inhibition of proliferation. The higher sensitivity to GCK knockdown in RASmut cells suggests that targeting GCK is especially effective in multiple myeloma which harbors RAS mutations. To exclude a potential off-target effect associated with GCK knockdown that led to the inhibition of MM proliferation, we set up an shGCK-resistant GCK allele (GCKshRNA-RES) by introducing mismatch mutations on the shRNA targeted sequences without changing the encoded amino acids. In the shGCK rescue experiment using GCKshRNA-RES we showed that all shRNA induced phenotypes (lack of growth, apoptosis and downstream effectors decrease) were corrected by the GCK resistant allele expression, ruling out the off-target hypothesis. Moreover, we expanded the in vivo studies of GCK knockdown on MM tumor progression. To monitor the tumor progression, we transduced MM.1S cells with firefly luciferase and established an inducible GCK knockdown system. Luciferase-expressing GCK inducible knockdown MM cells or non-targeting control shRNA (shCNTL) transduced MM cells were s.c. injected into SCID/Beige mice and the tumor progression was monitored by bioluminescence imaging. Doxycycline (for induction of shRNA) or vehicle treatment were started after the tumor was established on day 16 to induce shGCK and subsequently silence GCK expression. In contrast to the vehicle-treated MM.1S-Tet-on-shGCK or doxycycline-treated MM.1S-Tet-on-shCNTL tumors, doxycycline-treated animals bearing MM.1S-Tet-on-shGCK xenografts showed a significant inhibition (P<0.001) of tumor growth (Figure 2). Thus, GCK is also required for tumor growth. Lysine 45 is critical for GCK kinase activity. Point mutation of K45A will completely abolish its kinase activity. We introduced K45A mutation into GCKshRNA-RES (GCKshRNA-RESK45A→ shGCK resistant and kinase dead GCK). Tet-on-shGCK with GCKshRNA-RES or GCKshRNA-RESK45A were co-transduced in MM.1S cells. As expected, the GCK knockdown effects were rescued by GCKshRNA-RES but not by the kinase-dead mutant GCKshRNA-RESK45A. In contrast to GCKshRNA-RES, GCKshRNA-RESK45A failed to stimulate MM cell proliferation, to suppress MM cells apoptosis and to restore the downstream effectors expression. Our findings demonstrated that GCK kinase activity is required for its function in myeloma cell physiology. Conclusion: Taken together, our findings provide a rationale for the clinical evaluation of targeting GCK in MM patients and the role of GCK in MM tumorigenesis as well as drug resistance. The subsequent development of small molecules inhibiting this pathway, such as GCK kinase inhibitors, will address the unmet need of developing targeted treatments for RASmut myeloma and potentially for other RASmut malignancies.

MOB (Mps one Binder) Proteins in the Hippo Pathway and Cancer.

The family of MOBs (monopolar spindle-one-binder proteins) is highly conserved in the eukaryotic kingdom. MOBs represent globular scaffold proteins without any known enzymatic activities. They can act as signal transducers in essential intracellular pathways. MOBs have diverse cancer-associated cellular functions through regulatory interactions with members of the NDR/LATS kinase family. By forming additional complexes with serine/threonine protein kinases of the germinal centre kinase families, other enzymes and scaffolding factors, MOBs appear to be linked to an even broader disease spectrum. Here, we review our current understanding of this emerging protein family, with emphases on post-translational modifications, protein-protein interactions, and cellular processes that are possibly linked to cancer and other diseases. In particular, we summarise the roles of MOBs as core components of the Hippo tissue growth and regeneration pathway.

The Inhibition of Gck Affect MAPK Cascade in Multiple Myeloma

Introduction: Germinal Center Kinase (GCK) is an essential regulator of stress-activated MAPK core signaling pathways. Recent studies revealing the role of GCK in tumorigenesis and cancer progression have generated increasing interest in validating GCK as a therapeutic target in cancer. We previously showed that GCK inhibition results in significant anti-MM effects by inducing cell cycle arrest and cell apoptosis accompanied by IKZF1/3 down regulation (Li et al, Blood 2017 130:1795). Our further research established GCK as a critical kinase in MM and as an attractive target for treatment of MM.Methods and Results: The over-expression of GCK in primary MM compared to normal cells was confirmed by immunohistochemistry staining of primary MM patient bone marrow biopsies. By quantitatively comparing the staining scores of GCK of primary MM patient bone marrows (n=26) and normal donor bone marrows (n=26), we found a significantly higher GCK expression (p<0.001) in MM patient BM samples (98%) compared to healthy donor BM samples (47%) (Figure 1). GCK protein expression level was induced by several cytokines that are critically involved in MM cell survival and proliferation including IL-6, TNF-a, LPS and CD40L in MM cells after treatment for 1h. The role of GCK expression in MM signaling transduction and tumor progression was addressed by inducible GCK-knockdown in MM cells. By generating Tet-on-shGCK-MM cell lines, we found that doxycycline-induced GCK silencing blocks IL-6 induced phosphorylation of MKK4, MKK7, JNK and ERK in MM.1S cells. Moreover, knockdown of GCK causes downregulation of IKZF1/3, c-MYC and BCL-6 in MM cells.To exclude the off-target effects of the GCK-shRNA and confirm the specific and critical role of GCK, we further generated recombinant GCK-WT and GCK-shRNA resistant allele construct with C-terminal c-Myc tag, and introduced them into the GCK inducible KD cells to determine if shRNA-resistant GCK can rescue the growth inhibition induced by the shRNA. Tet-on-shGCK-RPMI-8266 cells transduced with empty vector (EV) or GCK wild-type with c-Myc tag (WT) or GCK shRNA resistant mutation with c-myc tag (MT) were generated by routine lentiviral infection. Doxycycline-induced tet-on-shGCK expression resulted in significant decrease of GCK protein. Both endogenous GCK and wild-type GCK-c-Myc expressions were silenced. In contrast, expression of GCK shRNA resistant allele with c-Myc tag (MT) was not affected. The rescue effects of this allele on MM cells growth inhibition are undergoing.Bay 61-3606 is a small molecule that selectively inhibits GCK activity and shows promising anti-MM effects in our previous in vitro and in vivo studies. To further confirm the mechanism of GCK inhibition, we examined its effects on the MAPK cascade and found that pharmacologic blockade of GCK by Bay 61-3606 dose-dependently downregulated ERK, p38 and JNK phosphorylation in MM cells.In MM, IMiDs treatment leads to the selective ubiquitination and degradation of IKZF1 and IKZF3 by the CRBN-CRL4 ubiquitin ligase. Suppression of CRBN in MM cell lines induces IMiDs resistance. To our surprise, in MM cells with CRBN-knockdown, Bay 61-3606 retained the ability to decrease IKZF1 protein level and inhibit MM cell growth, indicating that GCK-induced IKZF1 downregulation is independent of CRBN. Thus, this study further validates the therapeutic potential of GCK inhibitors in IMiDs-resistant MM.Conclusion: Our findings show that GCK is overexpressed in MM and an attractive target for multiple myeloma therapy. The inhibition of GCK blocks the phosphorylation and activation of MAPK cascade, and induces the degradation of the substrate proteins IKZF1, IKZF3 and c-Myc, (Figure 2.). These studies further confirm the critical role of GCK in MM tumorigenesis. GCK inhibitors represent a novel anti-MM therapy especially in relapsed and IMiDs-resistant MM patients. [Display omitted] DisclosuresLentzsch:Caelum Biosciences: Consultancy, Other: Dr. Lentzsch recused herself as an investigator from the Phase 1a/b trial testing CAEL-101 in 11/2017., Patents & Royalties: Shareholder for Caelum Biosiences; Janssen: Consultancy; Bayer: Consultancy; BMS: Consultancy.

The germinal centre kinase Don3 is crucial for unconventional secretion of chitinase Cts1 in Ustilago maydis

Unconventional secretion has emerged as an increasingly important cellular process in eukaryotic cells. The underlying translocation mechanisms are diverse and often little understood. We study unconventional secretion of chitinase Cts1 in the corn smut fungus Ustilago maydis. This protein participates in the cytokinesis of yeast cells. During budding it localizes to the septated fragmentation zone where it presumably functions in the degradation of remnant chitin to allow separation of mother and daughter cell. However, the mechanistic details of Cts1 export remain unclear.Here we investigated the mechanism of unconventional Cts1 secretion with a focus on cytokinesis. Cell-cycle inhibition experiments supported the hypothesis that Cts1 export is connected to cytokinesis. To substantiate this finding we analysed gene deletion mutants impaired in cell separation and discovered that strains defective in secondary septum formation were affected in Cts1 export. The germinal centre kinase Don3 had a particularly strong influence on unconventional secretion. Using a synthetic switch, we unambiguously verified an essential role of Don3 for cytokinesis-dependent Cts1 export via the fragmentation zone. Thus, we gained novel insights into the mechanism of unconventional secretion and discovered the first regulatory component of this process.

Evolutionary history of Mo25 gene in plants, a component of RAM/MOR signaling network

Change in cell morphogenesis is an important feature for proper development of eukaryotes. It is necessary for cell polarity and asymmetry and is essential for asymmetric cell division. RAM/MOR is a conserved signaling network that coordinates cell polarity determinants important for asymmetric cell division and cell polarity establishment. Mo25 is a scaffold protein that acts as a master regulator of the germinal center kinase (GCK) which triggers the downstream signaling of this network. Little is known about RAM/MOR network or Mo25 protein homologs in plants. Here, we provide a glimpse of the evolutionary gene history of Mo25 in green plants. Our data showed that a duplication of Mo25 occurred at the basis of land plants (Embryophyta), forming the groups Mo25A and Mo25B. Further duplication events occurred in other plant lineages and one subgroup of sequences seemed to be rapidly diverging. This subgroup contained an A. thaliana paralog (AtMo25-1) which lacks intron and is expressed in a similar fashion of retrogenes (i.e. low expression levels and narrow expression breadth), suggesting that this paralog was duplicated by retroposition. We also showed that all AtMo25 proteins are structurally similar to each other and to the human homolog, although differences in residues in the interface between human Mo25 and MST3 are observed in the A. thaliana homologs. Expression profile of AtMo25 homologs suggest that they are required at different developmental contexts, possibly interacting with different partners. Finally, we discuss whether Mo25 duplication in Embryophyta could be an evolutionary novelty important for the terrestrial environment conquest and whether the duplicated paralogs are undergoing neo- or subfunctionalization.

A Hippo Pathway-Related GCK Controls Both Sexual and Vegetative Developmental Processes in the Fungus Sordaria macrospora.

The supramolecular striatin-interacting phosphatases and kinases (STRIPAK) complex is conserved from yeast to human, and regulates a variety of key biological processes. In animals, this complex consists of the scaffold protein striatin, the protein phosphatase 2A, and kinases, such as germinal center kinase (GCK) III and GCKIV family members, as well as other associated proteins. The STRIPAK complex was identified as a negative regulator of the Hippo pathway, a large eukaryotic signaling network with a core composed of a GCK and a nuclear Dbf2-related kinase. The signaling architecture of the Hippo core resembles the fungal septation initiation network (SIN) that regulates cytokinesis in fission yeast as well as septation in filamentous fungi. In the filamentous model fungus Sordaria macrospora, core components of the STRIPAK complex have been functionally described and the striatin homolog PRO11 has been shown to interact with the GCK SmKIN3. However, the exact role of SmKIN3 in fungal development has not yet been fully elucidated. Here, we provide comprehensive genetic and functional analysis of SmKIN3 from S. macrospora. Using deletion mutants and site-directed mutagenesis, along with phenotypic and phylogenetic analysis, we provide compelling evidence that SmKIN3 is involved in fruiting body formation, hyphal fusion, and septation. Strains carrying the ATP-binding mutant SmKIN3K39R, as well as a double-deletion strain lacking SmKIN3 and the core STRIPAK subunit PRO11, also revealed severe developmental defects. Collectively, this study suggests that SmKIN3 links both the SIN and STRIPAK complex, thereby regulating multiple key cellular processes.

AcAxl2 and AcMst1 regulate arthrospore development and stress resistance in the cephalosporin C producer Acremonium chrysogenum.

The filamentous fungus Acremonium chrysogenum is the primordial producer of the β-lactam antibiotic cephalosporin C. This antibiotic is of major biotechnological and medical relevance because of its antibacterial activity against Gram-positive and Gram-negative bacteria. Antibiotic production during the lag phase of fermentation is often accompanied by a typical morphological feature of A. chrysogenum, the fragmentation of the mycelium into arthrospores. Here, we sought to identify factors that regulate the hyphal septation process and present the first comparative functional characterization of the type I integral plasma membrane protein Axl2 (axial budding pattern protein 2), a central component of the bud site selection system (BSSS) and Mst1 (mammalian Sterile20-like kinase), a septation initiation network (SIN)-associated germinal center kinase (GCK). Although an Acaxl2 deletion strain showed accelerated arthrospore formation after 96h in liquid culture, deletion of Acmst1 led to a 24h delay in arthrospore development. The overexpression of Acaxl2 resulted in an arthrospore formation similar to the A3/2 strain. In contrast to this, A3/2::Acmst1 OE strain displayed an enhanced arthrospore titer. Large-scale stress tests revealed an involvement of AcAxl2 in controlling osmotic, endoplasmic reticulum, and cell wall stress response. In a similar approach, we found that AcMst1 plays an essential role in regulating growth under osmotic, cell wall, and oxidative stress conditions. Microscopic analyses and plating assays on media containing Calcofluor White and NaCl showed that arthrospore development is a stress-dependent process. Our results suggest the potential for identifying candidate genes for strain improvement programs to optimize industrial fermentation processes.

Suppression of Th17 cell differentiation by misshapen/NIK-related kinase MINK1.

T helper type 17 cells (Th17 cells) are major contributors to many autoimmune diseases. In this study, we demonstrate that the germinal center kinase family member MINK1 (misshapen/NIK-related kinase 1) negatively regulates Th17 cell differentiation. The suppressive effect of MINK1 on induction of Th17 cells is mediated by the inhibition of SMAD2 activation through direct phosphorylation of SMAD2 at the T324 residue. The importance of MINK1 to Th17 cell differentiation was strengthened in the animal model of experimental autoimmune encephalomyelitis (EAE). Moreover, we show that the reactive oxygen species (ROS) scavenger N-acetyl cysteine boosts Th17 cell differentiation in a MINK1-dependent manner and exacerbates the severity of EAE. Thus, we have not only established MINK1 as a critical regulator of Th17 cell differentiation, but also clarified that accumulation of ROS may limit the generation of Th17 cells. The contribution of MINK1 to ROS-regulated Th17 cell differentiation may suggest an important mechanism for the development of autoimmune diseases influenced by antioxidant dietary supplements.

Molecular cloning, characterization and function of a germinal center kinase MST4 gene from Litopenaeus vannamei in response to Vibrio alginolyticus challenge in TLR-TRAF6 signaling pathway

The serine/threonine protein kinase MST4 plays multiple roles in the regulation of signaling pathways that govern cellular processes including mitosis, migration, homeostasis, polarity, proliferation, differentiation and apoptosis. Here we report the identification and characterization of the full-length sequence of LvMST4 from the shrimp L. vannamei, and investigations into its role in the shrimp's immune response to infection by the pathogenic bacterium Vibrio alginolyticus. Subcellular localization assays demonstrated the enzyme's presence in the shrimp's cytoplasm, and tissue-specific expression analysis revealed that it is expressed ubiquitously but at different levels in different tissues. Infection with V. alginolyticus increased LvMST4 expression and induced a rapid response via the TLR-TRAF6 signaling pathway, causing a decline in the total hemocyte count (THC) and an increase in respiratory burst (RB) activity. In non-infected shrimp, RNAi silencing of LvMST4 with dsRNA had no significant effect on THC but seemed to activate the TRAF6-MKK6-p38 pathway and reduced RB activity. In shrimp challenged with V. alginolyticus, LvMST4 silencing reduced bacterial clearance and increased the initial upregulation of LvTRAF6 while reducing the expression of LvMKK6 and Lvp38. LvMST4 silencing also slightly reduced the THC but caused pronounced increases in RB activity and cumulative mortality. These findings suggest that LvMST4 contributes to antimicrobial responses via the TLR-TRAF6 signal pathway, and helps maintain immunological homeostasis in L. vannamei.

Divergent synthesis of kinase inhibitor derivatives, leading to discovery of selective Gck inhibitors

We accomplished divergent synthesis of potent kinase inhibitor BAY 61-3606 (1) and 27 derivatives via conjugation of imidazo[1,2-c]pyrimidine and indole ring compounds with aromatic (including pyridine) derivatives by means of palladium-catalyzed cross-coupling reaction. Spleen tyrosine kinase (Syk) and germinal center kinase (Gck, MAP4K2) inhibition assays showed that some of the synthesized compounds were selective Gck inhibitors.

CCM-3 Promotes C. elegans Germline Development by Regulating Vesicle Trafficking Cytokinesis and Polarity

Cerebral cavernous malformations (CCMs) are vascular defects of the CNS that arise from loss of integrity of the endothelial cells lining blood capillaries, causing leakage of blood into the brain [1]. This results in headaches, seizures, and/or hemorrhagic stroke, depending on the location of the lesion. CCM affects 0.5% of the population and follows anautosomal dominant inheritance pattern caused bymutations in one of the three genes: CCM1 (gene name KRIT1), CCM2 (also known as malcavernin orOSM), and CCM3 (gene name PDCD10) [2, 3], with the earliest onset and most severe prognosis occurring in CCM3 patients [4]. The three CCM genes encode structurally distinct scaffold proteins that function in multiple complexes [5-9]. Using the C.elegans germline as a model of multicellular tube development, we show here that CCM-3 is enriched at the luminal membrane of the germline and the contractile ring of dividing cells in the embryo. Loss of ccm-3 results in defective RAB-11-mediated endocytic recycling, which in turn is necessary for gonadal lumen (rachis) formation, completion of cytokinesis, and localization of cell-surface receptors. CCM-3-mediated localization of anillin and non-muscle myosin to the lateral surfaces of germ cells is required for proper cytoskeletal organization, subsequent oocyte growth, and localization of polarity proteins. Biochemical analysis reveals conservation of the STRIPAK complex and distinct roles for GCK-1 (germinal center kinase III family protein) and striatin/CASH-1 in controlling the localization and function of CCM-3. Taken together, our data establish CCM-3 as a novel regulator of rachis lumenization and polarity establishment during embryogenesis.

Deficiency of X-Linked Protein Kinase Nrk during Pregnancy Triggers Breast Tumor in Mice

The onset and/or growth of breast tumor are controlled, at least in part, by estrogen. Therefore, to prevent the development of breast tumor, estrogen-dependent proliferation of mammary epithelial cells during pregnancy needs to be suppressed once the mammary gland is fully developed to enable lactation. However, the underlying molecular mechanisms remain unknown. Nrk is an X-linked protein serine/threonine kinase in the germinal center kinase family. Herein, we demonstrate a frequent occurrence of breast tumors in homozygous and heterozygous Nrk mutant mice that have experienced pregnancy/parturition. The tumors never developed in the mutant mice without a history of pregnancy/parturition. They exhibited histopathological features of noninvasive tubular adenocarcinoma, and expressed estrogen receptor α. At late gestation when estrogen receptor α expression was significantly reduced in the wild-type mammary gland, grossly normal mammary glands in the pregnant Nrk mutant mice occasionally contained hyperplastic foci continuously expressing the receptor. Consistently, Nrk expression was induced in the wild-type mammary gland at this period of pregnancy. On the other hand, the pregnant Nrk mutant mice also showed elevated blood estrogen levels at late gestation. We suggest that Nrk suppresses the excessive proliferation of mammary epithelial cells during pregnancy, and the impairment of this regulatory system leads to frequent occurrence of breast tumor in Nrk mutant mice.

Pathophysiological significance and therapeutic targeting of germinal center kinase in diffuse large B-cell lymphoma

AbstractDiffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma, yet 40% to 50% of patients will eventually succumb to their disease, demonstrating a pressing need for novel therapeutic options. Gene expression profiling has identified messenger RNAs that lead to transformation, but critical events transforming cells are normally executed by kinases. Therefore, we hypothesized that previously unrecognized kinases may contribute to DLBCL pathogenesis. We performed the first comprehensive analysis of global kinase activity in DLBCL, to identify novel therapeutic targets, and discovered that germinal center kinase (GCK) was extensively activated. GCK RNA interference and small molecule inhibition induced cell-cycle arrest and apoptosis in DLBCL cell lines and primary tumors in vitro and decreased the tumor growth rate in vivo, resulting in a significantly extended lifespan of mice bearing DLBCL xenografts. GCK expression was also linked to adverse clinical outcome in a cohort of 151 primary DLBCL patients. These studies demonstrate, for the first time, that GCK is a molecular therapeutic target in DLBCL tumors and that inhibiting GCK may significantly extend DLBCL patient survival. Because the majority of DLBCL tumors (∼80%) exhibit activation of GCK, this therapy may be applicable to most patients.

Timely Closure of the Prospore Membrane Requires SPS1 and SPO77 in Saccharomyces cerevisiae.

During sporulation in Saccharomyces cerevisiae, a double lipid bilayer called the prospore membrane is formed de novo, growing around each meiotic nucleus and ultimately closing to create four new cells within the mother cell. Here we show that SPS1, which encodes a kinase belonging to the germinal center kinase III family, is involved in prospore membrane development and is required for prospore membrane closure. We find that SPS1 genetically interacts with SPO77 and see that loss of either gene disrupts prospore membrane closure in a similar fashion. Specifically, cells lacking SPS1 and SPO77 produce hyperelongated prospore membranes from which the leading edge protein complex is not removed from the prospore membrane in a timely fashion. The SPS1/SPO77 pathway is required for the proper phosphorylation and stability of Ssp1, a member of the leading edge protein complex that is removed and degraded when the prospore membrane closes. Genetic dissection of prospore membrane closure finds SPS1 and SPO77 act in parallel to a previously described pathway of prospore membrane closure that involves AMA1, an activator of the meiotic anaphase promoting complex.

MINK1 kinase suppresses TH17 differentiation and autoimmune inflammation via inhibition of the TGF-β pathway

Abstract TH17 cells (interleukin-17-producing helper T cells) are present at the sites of tissue inflammation and associated with the induction of multiple autoimmune diseases. The differentiation of TH17 cells is instructed and critically regulated by various cytokines in the microenvironment, which drive intracellular signaling pathways and transcription profiles that determine the cell fate. Here we show that MINK1, a germinal center kinase (GCK) family kinase, plays as a negative regulator for TH17 cell differentiation. Mink1−/− mice has higher frequency of TH17 cells in vivo and developed more severe experimental autoimmune encephalomyelitis (EAE) than wild type (WT) mice. Further experiments revealed that MINK1 directly interacts with SMAD2 and phosphorylates SAMD2 at T324 residue in its α-helix 1 region, which inhibits the C-terminal phosphorylation (activation) of SMAD2. Moreover, we found that MINK1 kinase is activated by T cell receptor stimulation in a ROS (reactive oxygen species)-dependent manner, which can be compromised by ROS scavenger N-acetyl cysteine (NAC). Accordingly, NAC treatment markedly boost the in vitro induction of TH17 cells in a MINK1-dependent manner and potentiates TH17 cells generation and development of EAE in vivo. In sum, our data not only demonstrate a regulatory role of MINK1 kinase in TH17 cell differentiation, but also provide the molecular insight into a possible mechanism, by which increased dietary antioxidants supplement might represent a health risk factor for the development of autoimmune diseases through increased induction of TH17 cells.

Traf2- and Nck-interacting kinase (TNIK) is involved in the anti-cancer mechanism of dovitinib in human multiple myeloma IM-9 cells.

Traf2- and Nck-interacting kinase (TNIK) is a member of the germinal center kinase family. TNIK was first identified as a kinase that is involved in regulating cytoskeletal organization in many types of cells, and it was recently proposed as a novel therapeutic target in several types of human cancers. Although previous studies suggest that TNIK plays a pivotal role in cancer cell survival and prognosis, its function in hematological cancer cell survival has not been investigated. Here we investigated the relationship between TNIK function and cell viability in multiple myeloma IM-9 cells using TNIK small interfering RNA (siRNA) transfection and dovitinib treatment. Treatment of IM-9 cells with TNIK siRNA and dovitinib treatment reduced cell proliferation. The ATP competing kinase assay and western blot analysis showed that dovitinib strongly inhibited both the interaction of TNIK with ATP (K i, 13nM) and the activation of Wnt signaling effectors such as β-catenin and TCF4. Dovitinib also induced caspase-dependent apoptosis in IM-9 cells without significant cytotoxicity in PBMCs. Our results provide new evidence that TNIK may be involved in the proliferation of multiple myeloma IM-9 cells and in the anti-cancer activity of dovitinib via inhibition of the endogenous Wnt signaling pathway.