Regulation of stress-responsive mitogen-activated protein (MAP) kinase pathways by TAO2

Expanding the phenotype and genotype spectrum of TAOK1 neurodevelopmental disorder and delineating TAOK2 neurodevelopmental disorder

PURPOSE

The thousand and one kinase (TAOK) proteins are a group of serine/threonine-protein kinases involved in signaling pathways, cytoskeleton regulation, and neuronal development. TAOK1 variants are associated with a neurodevelopmental disorder (NDD) characterized by distinctive facial features, hypotonia, and feeding difficulties. TAOK2 variants have been reported to be associated with autism and early-onset obesity. However, a distinct TAOK2-NDD has not yet been delineated.

METHODS

We retrospectively studied the clinical and genetic data of individuals recruited from several centers with TAOK1 and TAOK2 variants that were detected through exome and genome sequencing.

RESULTS

We report 50 individuals with TAOK1 variants with associated phenotypes, including neurodevelopmental abnormalities (100%), macrocephaly (83%), and hypotonia (58%). We report male genital anomalies and hypoglycemia as novel phenotypes. Thirty-seven unique TAOK1 variants were identified. Most of the missense variants clustered in the protein kinase domain at residues that are intolerant to missense variation. We report 10 individuals with TAOK2 variants with associated phenotypes, including neurodevelopmental abnormalities (100%), macrocephaly (75%), autism (75%), and obesity (70%).

CONCLUSION

We describe the largest cohort of TAOK1-NDD to date, to our knowledge, expanding its phenotype and genotype spectrum with 30 novel variants. We delineated the phenotype of a novel TAOK2-NDD associated with neurodevelopmental abnormalities, autism, macrocephaly, and obesity.

Research progress on anti-tumor mechanism of TAOK kinases

Thousand and one amino-acid protein kinases(TAOKs), as a key member of the mitogen-activated protein kinase (MAPK) cascade, has recently attracted widespread attention in the field of anti-cancer research. There are three members of this subfamily: TAOK1, TAOK2, and TAOK3. Studies have shown that members of the TAOK family participate in regulating cell proliferation, apoptosis, migration, and invasion through various pathways, thereby playing an important role in tumorigenesis and progression. This review summarizes the functions of TAOK kinases in tumor cell signal transduction, cell cycle regulation, and the tumor microenvironment, with a particular emphasis on its potential as a target for anti-cancer drugs. Future research will further elucidate the specific mechanisms of action of TAOK kinase in different types of tumors and explore its clinical application prospects.

Long Non-Coding RNA AC008972.1 as a Novel Therapeutic Target for Prostate Cancer

Background: Prostate cancer is a common male malignancy and the leading cause of cancer death in men. Long non-coding RNAs (lncRNAs), microRNA (miRNAs) and mRNAs networks mediate prostate cancer progression. Herein, we investigated the functions of lncRNA AC008972.1 and its regulatory mechanism in prostate cancer. Materials and Methods: The expression levels of lncRNA AC008972.1, miR-143-3p, and TAOK2 were detected in prostate cancer tissues and cell lines by reverse transcription-quantitative polymerase chain reaction. PC3 and LNCaP cells were used to establish lncRNA AC008972.1-knockdown, miR-143-3p-overexpressing, and thousand-and-one-amino acid 2 kinase (TAOK2)-downregulated cells. Cell viability was examined by MTT assays and cell proliferation was detected by clone formation assay. Cell migration and invasion were detected by wound scratch assay and transwell chamber assay. The apoptosis rate was analyzed by flow cytometry. The protein expression was detected by Western blot assay. The RNA interaction was explored and validated by RNA binding protein immunoprecipitation (RIP) assay and dual luciferase activity assay. A mouse xenograft model was established to investigate the effect of lncRNA AC008972.1 on prostate cancer progression. Results: High expression of lncRNA AC008972.1 was associated with low overall survival in prostate cancer patients. Downregulation of lncRNA AC008972.1 suppressed prostate cancer progression by inhibiting cell viability, proliferation, migration, and invasion, in addition to the EMT process, whereas cell apoptosis was significantly promoted. LncRNA AC008972.1 bound with miR-143-3p and negatively regulated miR-143-3p expression. MiR-143-3p overexpression suppressed prostate cancer malignant behaviors in vitro. TAOK2 expression was decreased by miR-143-3p through the complementary targeting of TAOK2 mRNA. Downregulation of lncRNA AC008972.1 mitigated prostate cancer malignant behaviors in vitro based on miR-143-3p/TAOK2 node. Furthermore, the data of xenograft model experiment showed that inhibition of lncRNA AC008972.1 suppressed tumor growth in vivo. Conclusions: Knockdown of lncRNA AC008972.1 inhibits prostate cancer cell growth via downregulation of TAOK2 induced by miR-143-3p. LncRNA AC008972.1 acts as an oncogene in the progression of prostate cancer and may provide a novel therapeutic target for prostate cancer.

The autism susceptibility kinase, TAOK2, phosphorylates eEF2 and modulates translation

Genes implicated in translation control have been associated with autism spectrum disorders (ASDs). However, some important genetic causes of autism, including the 16p11.2 microdeletion, bear no obvious connection to translation. Here, we use proteomics, genetics, and translation assays in cultured cells and mouse brain to reveal altered translation mediated by loss of the kinase TAOK2 in 16p11.2 deletion models. We show that TAOK2 associates with the translational machinery and functions as a translational brake by phosphorylating eukaryotic elongation factor 2 (eEF2). Previously, all signal-mediated regulation of translation elongation via eEF2 phosphorylation was believed to be mediated by a single kinase, eEF2K. However, we show that TAOK2 can directly phosphorylate eEF2 on the same regulatory site, but functions independently of eEF2K signaling. Collectively, our results reveal an eEF2K-independent signaling pathway for control of translation elongation and suggest altered translation as a molecular component in the etiology of some forms of ASD.

Pleiotropic functions of TAO kinases and their dysregulation in neurological disorders

Thousand and one amino acid kinases (TAOKs) are relatively understudied and functionally pleiotropic protein kinases that have emerged as important regulators of neurodevelopment. Through their conserved amino-terminal catalytic domain, TAOKs mediate phosphorylation at serine/threonine residues in their substrates, but it is their divergent regulatory carboxyl-terminal domains that confer both exquisite functional specification and cellular localization. In this Review, we discuss the physiological roles of TAOKs and the intricate signaling pathways, molecular interactions, and cellular behaviors they modulate-from cell stress responses, division, and motility to tissue homeostasis, immunity, and neurodevelopment. These insights are then integrated into an analysis of the known and potential impacts of disease-associated variants of TAOKs, with a focus on neurodevelopmental disorders, pain and addiction, and neurodegenerative diseases. Translating this foundation into clinical benefits for patients will require greater structural and functional differentiation of the TAOKs afforded by their individually specialized domains.

Novel 1,2,3-Triazole-Containing Quinoline-Benzimidazole Hybrids: Synthesis, Antiproliferative Activity, In Silico ADME Predictions, and Docking

The newly synthesized quinoline-benzimidazole hybrids containing two types of triazole-methyl-phenoxy linkers were characterized via NMR and elemental analysis. Additional derivatization was achieved by introducing bromine at the C-2 position of the phenoxy core. These novel hybrids were tested for their effects on the growth of the non-tumor cell line MRC-5 (human fetal lung fibroblasts), leukemia and lymphoma cell lines: Hut78, THP-1 and HL-60, and carcinoma cell lines: HeLa and CaCo-2. The results obtained, presented as the concentration that achieves 50% inhibition of cell growth (IC50 value), show that the compounds tested affect tumor cell growth differently depending on the cell line and the dose applied (IC50 ranged from 0.2 to >100 µM). The quinoline-benzimidazole hybrids tested, including 7-chloro-4-(4-{[4-(5-methoxy-1H-1,3-benzo[d]imidazol-2-yl)phenoxy]methyl}-1H-1,2,3-triazol-1-yl)quinoline 9c, 2-(3-bromo-4-{[1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazol-4-yl]methoxy}phenyl)-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 10e, 2-{4-[(1-{2-[(7-chloroquinolin-4-yl)amino]ethyl}-1H-1,2,3-triazol-4-yl)methoxy]phenyl}-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 14e and 2-{3-bromo-4-[(1-{2-[(7-chloroquinolin-4-yl)amino]ethyl}-1H-1,2,3-triazol-4-yl)methoxy]phenyl}-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 15e, arrested the cell cycle of lymphoma (HuT78) cells. The calculated ADMET properties showed that the synthesized compounds violated at most two of Lipinski's rules, making them potential drug candidates, but mainly for parenteral use due to low gastrointestinal absorption. The quinoline-benzimidazole hybrid 14e, which was shown to be a potent and selective inhibitor of lymphoma cell line growth, obtained the highest binding energy (-140.44 kcal/mol), by docking to the TAO2 kinase domain (PDB: 2GCD).

Tissue- and cell-type-specific molecular and functional signatures of 16p11.2 reciprocal genomic disorder across mouse brain and human neuronal models

Chromosome 16p11.2 reciprocal genomic disorder, resulting from recurrent copy-number variants (CNVs), involves intellectual disability, autism spectrum disorder (ASD), and schizophrenia, but the responsible mechanisms are not known. To systemically dissect molecular effects, we performed transcriptome profiling of 350 libraries from six tissues (cortex, cerebellum, striatum, liver, brown fat, and white fat) in mouse models harboring CNVs of the syntenic 7qF3 region, as well as cellular, transcriptional, and single-cell analyses in 54 isogenic neural stem cell, induced neuron, and cerebral organoid models of CRISPR-engineered 16p11.2 CNVs. Transcriptome-wide differentially expressed genes were largely tissue-, cell-type-, and dosage-specific, although more effects were shared between deletion and duplication and across tissue than expected by chance. The broadest effects were observed in the cerebellum (2,163 differentially expressed genes), and the greatest enrichments were associated with synaptic pathways in mouse cerebellum and human induced neurons. Pathway and co-expression analyses identified energy and RNA metabolism as shared processes and enrichment for ASD-associated, loss-of-function constraint, and fragile X messenger ribonucleoprotein target gene sets. Intriguingly, reciprocal 16p11.2 dosage changes resulted in consistent decrements in neurite and electrophysiological features, and single-cell profiling of organoids showed reciprocal alterations to the proportions of excitatory and inhibitory GABAergic neurons. Changes both in neuronal ratios and in gene expression in our organoid analyses point most directly to calretinin GABAergic inhibitory neurons and the excitatory/inhibitory balance as targets of disruption that might contribute to changes in neurodevelopmental and cognitive function in 16p11.2 carriers. Collectively, our data indicate the genomic disorder involves disruption of multiple contributing biological processes and that this disruption has relative impacts that are context specific.

Nuclear speckle integrity and function require TAO2 kinase

Nuclear speckles are non-membrane-bound organelles known as storage sites for messenger RNA (mRNA) processing and splicing factors. More recently, nuclear speckles have also been implicated in splicing and export of a subset of mRNAs, including the influenza virus M mRNA that encodes proteins required for viral entry, trafficking, and budding. However, little is known about how nuclear speckles are assembled or regulated. Here, we uncovered a role for the cellular protein kinase TAO2 as a constituent of nuclear speckles and as a factor required for the integrity of these nuclear bodies and for their functions in pre-mRNA splicing and trafficking. We found that a nuclear pool of TAO2 is localized at nuclear speckles and interacts with nuclear speckle factors involved in RNA splicing and nuclear export, including SRSF1 and Aly/Ref. Depletion of TAO2 or inhibition of its kinase activity disrupts nuclear speckle structure, decreasing the levels of several proteins involved in nuclear speckle assembly and splicing, including SC35 and SON. Consequently, splicing and nuclear export of influenza virus M mRNA were severely compromised and caused a disruption in the virus life cycle. In fact, low levels of TAO2 led to a decrease in viral protein levels and inhibited viral replication. Additionally, depletion or inhibition of TAO2 resulted in abnormal expression of a subset of mRNAs with key roles in viral replication and immunity. Together, these findings uncovered a function of TAO2 in nuclear speckle formation and function and revealed host requirements and vulnerabilities for influenza infection.

Research Advances in the Molecular Functions and Relevant Diseases of TAOKs, Novel STE20 Kinase Family Members

As serine/threonine-protein kinases, Thousand and One Kinases(TAOKs) are members of the GCKlike superfamily, one of two well-known branches of the Ste20 kinase family. Within the last two decades, three functionally similar kinases, namely TAOK1-3, were identified. TAOKs are involved in many molecular and cellular events. Scholars widely believe that TAOKs act as kinases upstream of the MAPK cascade and as factors that interact with MST family kinases, the cytoskeleton, and apoptosis-associated proteins. Therefore, TAOKs are thought to function in tumorigenesis. Additionally, TAOKs participate in signal transduction induced by Notch, TCR, and IL-17. Recent studies found that TAOKs play roles in a series of diseases and conditions, such as the central nervous system dysfunction, herpes viral infection, immune system imbalance, urogenital system malformation during development, cardiovascular events, and childhood obesity. Therefore, inhibitory chemicals targeting TAOKs may be of great significance as potential drugs for these diseases.

The Diverse Roles of TAO Kinases in Health and Diseases

Thousand and one kinases (TAOKs) are members of the MAP kinase kinase kinase (MAP3K) family. Three members of this subfamily, TAOK1, 2, and 3, have been identified in mammals. It has been shown that TAOK1, 2 and 3 regulate the p38 MAPK and Hippo signaling pathways, while TAOK 1 and 2 modulate the SAPK/JNK cascade. Furthermore, TAOKs are involved in additional interactions with other cellular proteins and all of these pathways modulate vital physiological and pathophysiological responses in cells and tissues. Dysregulation of TAOK-related pathways is implicated in the development of diseases including inflammatory and immune disorders, cancer and drug resistance, and autism and Alzheimer's diseases. This review collates current knowledge concerning the roles of TAOKs in protein-protein interaction, signal transduction, physiological regulation, and pathogenesis and summarizes the recent development of TAOK-specific inhibitors that have the potential to ameliorate TAOKs' effects in pathological situations.

Replicative and radiation-induced aging: a comparison of gene expression profiles

All living organisms are subject to the aging process and experience the effect of ionizing radiation throughout their life. There have been a number of studies that linked ionizing radiation process to accelerated aging, but comprehensive signalome analysis of both processes was rarely conducted. Here we present a comparative signaling pathway based analysis of the transcriptomes of fibroblasts irradiated with different doses of ionizing radiation, replicatively aged fibroblasts and fibroblasts collected from young, middle age and old patients. We demonstrate a significant concordance between irradiation-induced and replicative senescence signalome signatures of fibroblasts. Additionally, significant differences in transcriptional response were also observed between fibroblasts irradiated with high and low dose. Our data shows that the transcriptome of replicatively aged fibroblasts is more similar to the transcriptome of the cells irradiated with 2 Gy, than with 5 сGy.This work revealed a number of signaling pathways that are shared between senescence and irradiation processes and can potentially be targeted by the new generation of gero- and radioprotectors.

Apolipoprotein C1 (APOC1) promotes tumor progression via MAPK signaling pathways in colorectal cancer

Aim: Identifying high-efficiency prognostic markers for colorectal cancer (CRC) is necessary for clinical practice. Increasing evidence demonstrates that apolipoprotein C1 (APOC1) promotes carcinogenesis in some human cancers. However, the expression status and biological function of APOC1 in CRC remain unclear.

Materials and methods: We detected the association between APOC1 expression and clinicopathological features in 140 CRC patients by immunohistochemistry. Small interfering RNA (siRNA) technology was used to downregulate APOC1 expression in CRC cells. Cell proliferation was estimated by CCK8 and clonogenic assays. The cell cycle and apoptosis were analyzed by flow cytometry. Cell migration and invasion were examined by a transwell assay. Gene set enrichment analysis (GSEA) and protein expression of signaling pathways were used to suggest the possible APOC1-associated pathways in CRC.

Results: APOC1 was highly expressed in CRC tissues. High immunohistochemistry (IHC) expression of APOC1 was correlated with the N stage, M stage and TNM stage. High IHC APOC1 expression in CRC tissues was associated with poor prognosis. Univariate and multivariate Cox regression analyses showed that APOC1 was an independent risk factor for OS. Cell proliferation of CRC cell lines was inhibited by the downregulation of APOC1. Moreover, si-APOC1 transfection induced cell cycle arrest but low apoptosis increases by regulating the expression of related proteins. Cell migration and invasion were also inhibited by the downregulation of APOC1. The Cancer Genome Atlas Colorectal Adenocarcinoma (TCGA COAD-READ) dataset analyzed by GSEA showed that APOC1 might be involved in the mitogen-activated protein kinase (MAPK) signaling pathway, which was further preliminarily confirmed by Western blotting.

Conclusion: APOC1 was overexpressed in CRC tissues, and a high level of APOC1 contributed to a poor prognosis. APOC1 expression influenced the cell proliferation ability and motility capacity of CRC via the MAPK pathway. APOC1 could act as a novel prognostic biomarker in CRC.

Altered TAOK2 activity causes autism-related neurodevelopmental and cognitive abnormalities through RhoA signaling

Atypical brain connectivity is a major contributor to the pathophysiology of neurodevelopmental disorders (NDDs) including autism spectrum disorders (ASDs). TAOK2 is one of several genes in the 16p11.2 microdeletion region, but whether it contributes to NDDs is unknown. We performed behavioral analysis on Taok2 heterozygous (Het) and knockout (KO) mice and found gene dosage-dependent impairments in cognition, anxiety, and social interaction. Taok2 Het and KO mice also have dosage-dependent abnormalities in brain size and neural connectivity in multiple regions, deficits in cortical layering, dendrite and synapse formation, and reduced excitatory neurotransmission. Whole-genome and -exome sequencing of ASD families identified three de novo mutations in TAOK2 and functional analysis in mice and human cells revealed that all the mutations impair protein stability, but they differentially impact kinase activity, dendrite growth, and spine/synapse development. Mechanistically, loss of Taok2 activity causes a reduction in RhoA activation, and pharmacological enhancement of RhoA activity rescues synaptic phenotypes. Together, these data provide evidence that TAOK2 is a neurodevelopmental disorder risk gene and identify RhoA signaling as a mediator of TAOK2-dependent synaptic development.

Linking spatial gene expression patterns to sex-specific brain structural changes on a mouse model of 16p11.2 hemideletion

Neurodevelopmental disorders, such as ASD and ADHD, affect males about three to four times more often than females. 16p11.2 hemideletion is a copy number variation that is highly associated with neurodevelopmental disorders. Previous work from our lab has shown that a mouse model of 16p11.2 hemideletion (del/+) exhibits male-specific behavioral phenotypes. We, therefore, aimed to investigate with magnetic resonance imaging (MRI), whether del/+ animals also exhibited a sex-specific neuroanatomical endophenotype. Using the Allen Mouse Brain Atlas, we analyzed the expression patterns of the 27 genes within the 16p11.2 region to identify which gene expression patterns spatially overlapped with brain structural changes. MRI was performed ex vivo and the resulting images were analyzed using Voxel-based morphometry for T1-weighted sequences and tract-based spatial statistics for diffusion-weighted images. In a subsequent step, all available in situ hybridization (ISH) maps of the genes involved in the 16p11.2 hemideletion were aligned to Waxholm space and clusters obtained by sex-specific group comparisons were analyzed to determine which gene(s) showed the highest expression in these regions. We found pronounced sex-specific changes in male animals with increased fractional anisotropy in medial fiber tracts, especially in those proximate to the striatum. Moreover, we were able to identify gene expression patterns spatially overlapping with male-specific structural changes that were associated with neurite outgrowth and the MAPK pathway. Of note, previous molecular studies have found convergent changes that point to a sex-specific dysregulation of MAPK signaling. This convergent evidence supports the idea that ISH maps can be used to meaningfully analyze imaging data sets.

Role of granulosa cell mitogen-activated protein kinase 3/1 in gonadotropin-mediated meiotic resumption from diplotene arrest of mammalian oocytes

In mammals, preovulatory oocytes are encircled by several layers of granulosa cells (GCs) in follicular microenvironment. These follicular oocytes are arrested at diplotene arrest due to high level of cyclic nucleotides from encircling GCs. Pituitary gonadotropin acts at the level of encircling GCs and increases adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) and activates mitogen-activated protein kinase 3/1 (MAPK3/1) signaling pathway. The MAPK3/1 disrupts the gap junctions between encircling GCs and oocyte. The disruption of gap junctions interrupts the transfer of cyclic nucleotides to the oocyte that results a drop in intraoocyte cAMP level. A transient decrease in oocyte cAMP level triggers maturation promoting factor (MPF) destabilization. The destabilized MPF finally triggers meiotic resumption from diplotene arrest in follicular oocyte. Thus, MAPK3/1 from GCs origin plays important role in gonadotropin-mediated meiotic resumption from diplotene arrest in follicular oocyte of mammals.

MiR-422a targets MAPKK6 and regulates cell growth and apoptosis in colorectal cancer cells

The important role of miR-422a in tumor has been reported in several studies. Recent research discovered that the expression of miR-422a was significantly decreased in colorectal cancer tissues, providing miR-422a as a tumor suppressor in CRC. However, the concrete mechanism of miR-422a regulating CRC cell is still unclear. In this study, we demonstrated that miR-422a could inhibit CRC cell growth and promote cell apoptosis via in vitro analyses. Moreover, computational methods were adopted to identify the targets of miR-422a. We found MAPKK6 was the direct target of miR-422a. Consequently, we further elucidated that miR-422a inhibited CRC cell growth and induced cell apoptosis by inhibiting p38/MAPK pathway. Besides that, we established the tumor xenograft model using nude mice and the inhibitory effects on tumor volumes and weights by miR-422a mimic transfection were also detected. Taken together, these findings demonstrated miR-422a exerted anti-cancer activities on CRC, which could be potentially used for CRC prognosis prediction and treatment.

Importance of ERK1/2 in Regulation of Protein Translation during Oocyte Meiosis

Although the involvement of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathway in the regulation of cytostatic factor (CSF) activity; as well as in microtubules organization during meiotic maturation of oocytes; has already been described in detail; rather less attention has been paid to the role of ERK1/2 in the regulation of mRNA translation. However; important data on the role of ERK1/2 in translation during oocyte meiosis have been documented. This review focuses on recent findings regarding the regulation of translation and the role of ERK1/2 in this process in the meiotic cycle of mammalian oocytes. The specific role of ERK1/2 in the regulation of mammalian target of rapamycin (mTOR); eukaryotic translation initiation factor 4E (eIF4E) and cytoplasmic polyadenylation element binding protein 1 (CPEB1) activity is addressed along with additional focus on the other key players involved in protein translation.

Fundamental Elements in Autism: From Neurogenesis and Neurite Growth to Synaptic Plasticity

Autism spectrum disorder (ASD) is a set of neurodevelopmental disorders with a high prevalence and impact on society. ASDs are characterized by deficits in both social behavior and cognitive function. There is a strong genetic basis underlying ASDs that is highly heterogeneous; however, multiple studies have highlighted the involvement of key processes, including neurogenesis, neurite growth, synaptogenesis and synaptic plasticity in the pathophysiology of neurodevelopmental disorders. In this review article, we focus on the major genes and signaling pathways implicated in ASD and discuss the cellular, molecular and functional studies that have shed light on common dysregulated pathways using in vitro, in vivo and human evidence.

Highlights

Autism spectrum disorder (ASD) has a prevalence of 1 in 68 children in the United States.

ASDs are highly heterogeneous in their genetic basis.

ASDs share common features at the cellular and molecular levels in the brain.

Most ASD genes are implicated in neurogenesis, structural maturation, synaptogenesis and function.

RETRACTED: Generalized verrucosis and abnormal T cell activation due to homozygous TAOK2 mutation

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. The authors have notified the Editor of a serious error in their initial assumptions and, therefore, the overall conclusions presented in this article. The causative mutation is essential for the analysis and, therefore, it is difficult to correct part of the article. Had the Editor been aware of the issues flagged by the authors, the article would not have been accepted for publication. The authors have requested that the article is retracted because their data and conclusions are incorrect, and the Editor has agreed to retract the article.

Cancer-associated noncoding mutations affect RNA G-quadruplex-mediated regulation of gene expression

Cancer is a multifactorial disease driven by a combination of genetic and environmental factors. Many cancer driver mutations have been characterised in protein-coding regions of the genome. However, mutations in noncoding regions associated with cancer have been less investigated. G-quadruplex (G4) nucleic acids are four-stranded secondary structures formed in guanine-rich sequences and prevalent in the regulatory regions. In this study, we used published whole cancer genome sequence data to find mutations in cancer patients that overlap potential RNA G4-forming sequences in 5′ UTRs. Using RNAfold, we assessed the effect of these mutations on the thermodynamic stability of predicted RNA G4s in the context of full-length 5′ UTRs. Of the 217 identified mutations, we found that 33 are predicted to destabilise and 21 predicted to stabilise potential RNA G4s. We experimentally validated the effect of destabilising mutations in the 5′ UTRs of BCL2 and CXCL14 and one stabilising mutation in the 5′ UTR of TAOK2. These mutations resulted in an increase or a decrease in translation of these mRNAs, respectively. These findings suggest that mutations that modulate the G4 stability in the noncoding regions could act as cancer driver mutations, which present an opportunity for early cancer diagnosis using individual sequencing information.

MST-4 and TRAF-6 expression in the peripheral blood mononuclear cells of patients with Graves' disease and its significance

BACKGROUND

MST-4 and TRAF-6 are involved in the regulation of inflammatory and immune responses. However, whether they participate in the pathogenesis of Graves' disease (GD) has not yet been reported. Therefore, the purpose of this study was to investigate the expression of MST-4 and TRAF-6 in the peripheral blood of patients with GD to understand their role in the pathogenesis of GD.

METHODS

Thirty newly diagnosed GD patients, 24 GD patients in remission (eGD) and 30 normal controls (NC) were recruited. Thyroid function and autoantibody levels were determined using a chemiluminescence immunoassay. Peripheral blood mononuclear cells (PBMCs) were extracted, and MST-4 and TRAF-6 mRNA and protein levels were determined using real-time PCR and Western blotting, respectively.

RESULTS

1. Thyroid function in the GD group was significantly different from that in the eGD and NC groups (P < 0.05); however, there was no difference in thyroid function between the eGD group and the NC group (P > 0.05). The autoantibody levels in the NC group were significantly different from those in the GD and eGD groups (P < 0.05); however, the difference in the levels between the GD group and eGD group was not statistically significant (P > 0.05). 2. The MST-4 and TRAF-6 mRNA and protein levels in the GD group were significantly lower than those in the NC group (P < 0.05); however, there were no differences in mRNA and protein levels between the GD group and the eGD group or between the eGD group and the NC group (P > 0.05). 3. The correlation between the MST-4 and TRAF-6 mRNA and protein levels was not significant. However, there was a significant correlation between the TRAF-6 mRNA and TPO Ab levels in the eGD group and between the TRAF-6 mRNA and TR Ab levels in the NC group.

CONCLUSION

The MST-4 and TRAF-6 mRNA and protein levels were lower in the GD group than in the NC group, suggesting that MST-4 and TRAF-6 may be important in the pathogenesis of GD. Whether MST-4 influences the innate immune response through TRAF-6 and thus regulates the imbalance in downstream effector T cells requires further study. Investigating the expression of MST-4 and TRAF-6 in GD can provide a new perspective and targets for further study of the upstream mechanism responsible for effector T cell imbalance.

Activity-Based Protein Profiling Shows Heterogeneous Signaling Adaptations to BRAF Inhibition

Patients with BRAF V600E mutant melanoma are typically treated with targeted BRAF kinase inhibitors, such as vemurafenib and dabrafenib. Although these drugs are initially effective, they are not curative. Most of the focus to date has been upon genetic mechanisms of acquired resistance; therefore, we must better understand the global signaling adaptations that mediate escape from BRAF inhibition. In the current study, we have used activity-based protein profiling (ABPP) with ATP-analogue probes to enrich kinases and other enzyme classes that contribute to BRAF inhibitor (BRAFi) resistance in four paired isogenic BRAFi-naïve/resistant cell line models. Our analysis showed these cell line models, which also differ in their PTEN status, have considerable heterogeneity in their kinase ATP probe uptake in comparing both naïve cells and adaptations to chronic drug exposure. A number of kinases including FAK1, SLK, and TAOK2 had increased ATP probe uptake in BRAFi resistant cells, while KHS1 (M4K5) and BRAF had decreased ATP probe uptake in the BRAFi-resistant cells. Gene ontology (GO) enrichment analysis revealed BRAFi resistance is associated with a significant enhancement in ATP probe uptake in proteins implicated in cytoskeletal organization and adhesion, and decreases in ATP probe uptake in proteins associated with cell metabolic processes. The ABPP approach was able to identify key phenotypic mediators critical for each BRAFi resistant cell line. Together, these data show that common phenotypic adaptations to BRAF inhibition can be mediated through very different signaling networks, suggesting considerable redundancy within the signaling of BRAF mutant melanoma cells.

Impairments in dendrite morphogenesis as etiology for neurodevelopmental disorders and implications for therapeutic treatments

Dendrite morphology is pivotal for neural circuitry functioning. While the causative relationship between small-scale dendrite morphological abnormalities (shape, density of dendritic spines) and neurodevelopmental disorders is well established, such relationship remains elusive for larger-scale dendrite morphological impairments (size, shape, branching pattern of dendritic trees). Here, we summarize published data on dendrite morphological irregularities in human patients and animal models for neurodevelopmental disorders, with focus on autism and schizophrenia. We next discuss high-risk genes for these disorders and their role in dendrite morphogenesis. We finally overview recent developments in therapeutic attempts and we discuss how they relate to dendrite morphology. We find that both autism and schizophrenia are accompanied by dendritic arbor morphological irregularities, and that majority of their high-risk genes regulate dendrite morphogenesis. Thus, we present a compelling argument that, along with smaller-scale morphological impairments in dendrites (spines and synapse), irregularities in larger-scale dendrite morphology (arbor shape, size) may be an important part of neurodevelopmental disorders' etiology. We suggest that this should not be ignored when developing future therapeutic treatments.

Coordination of Recombination with Meiotic Progression in the Caenorhabditis elegans Germline by KIN-18, a TAO Kinase That Regulates the Timing of MPK-1 Signaling

Meiosis is a tightly regulated process requiring coordination of diverse events. A conserved ERK/MAPK-signaling cascade plays an essential role in the regulation of meiotic progression. The Thousand And One kinase (TAO) kinase is a MAPK kinase kinase, the meiotic role of which is unknown. We have analyzed the meiotic functions of KIN-18, the homolog of mammalian TAO kinases, in Caenorhabditis elegans. We found that KIN-18 is essential for normal meiotic progression; mutants exhibit accelerated meiotic recombination as detected both by analysis of recombination intermediates and by crossover outcome. In addition, ectopic germ-cell differentiation and enhanced levels of apoptosis were observed in kin-18 mutants. These defects correlate with ectopic activation of MPK-1 that includes premature, missing, and reoccurring MPK-1 activation. Late progression defects in kin-18 mutants are suppressed by inhibiting an upstream activator of MPK-1 signaling, KSR-2. However, the acceleration of recombination events observed in kin-18 mutants is largely MPK-1-independent. Our data suggest that KIN-18 coordinates meiotic progression by modulating the timing of MPK-1 activation and the progression of recombination events. The regulation of the timing of MPK-1 activation ensures the proper timing of apoptosis and is required for the formation of functional oocytes. Meiosis is a conserved process; thus, revealing that KIN-18 is a novel regulator of meiotic progression in C. elegans would help to elucidate TAO kinase's role in germline development in higher eukaryotes.

Differential Activation of Mitogen-Activated Protein Kinases, ERK 1/2, p38(MAPK) and JNK p54/p46 During Postnatal Development of Rat Hippocampus

Mitogen-activated protein kinases (MAPKs) are a group of serine-threonine kinases, including p38(MAPK), ERK 1/2 and JNK p54/p46, activated by phosphorylation in response to extracellular stimuli. The early postnatal period is characterized by significant changes in brain structure as well as intracellular signaling. In the hippocampus MAPKs have been involved in the modulation of development and neural plasticity. However, the temporal profile of MAPK activation throughout the early postnatal development is incomplete. An understanding of this profile is important since slight changes in the activity of these enzymes, in response to environmental stress in specific developmental windows, might alter the course of development. The present study was undertaken to investigate the hippocampal differential activation of MAPK during postnatal period. MAPK activation and total content were evaluated by Western blotting of hippocampal tissue obtained from male Wistar rats at postnatal days (P) 1, 4, 7, 10, 14, 21, 30 and 60. The total content and phosphorylation of each MAPK was expressed as mean ± SEM and then calculates as a percentile compared to P1 (set at 100 %). The results showed: (1) phosphorylation peaks of p38(MAPK) at PN4 (p = 0.036) and PN10 to PN60; (2) phosphorylation of ERK1 and ERK2 were increased with age (ERK1 p = 0.0000005 and ERK2 p = 0.003); (3) phosphorylation profile of JNK p54/p46 was not changed during the period analyzed (JNKp56 p = 0.716 and JNKp46 p = 0.192). Therefore, the activity profile of ERK 1/2 and p38(MAPK) during postnatal development of rat hippocampus are differentially regulated. Our results demonstrate that ERK 1/2 and p38(MAPK) are dynamically regulated during postnatal neurodevelopment, suggesting temporal correlation of MAPK activity with critical periods when programmed cell death and synaptogenesis are occurring. This suggests an important role for these MAPKs in postnatal development of rat hippocampus.

Sorafenib suppresses JNK-dependent apoptosis through inhibition of ZAK

Sorafenib is U.S. Food and Drug Adminstration-approved for the treatment of renal cell carcinoma and hepatocellular carcinoma and has been combined with numerous other targeted therapies and chemotherapies in the treatment of many cancers. Unfortunately, as with other RAF inhibitors, patients treated with sorafenib have a 5% to 10% rate of developing cutaneous squamous cell carcinoma (cSCC)/keratoacanthomas. Paradoxical activation of extracellular signal-regulated kinase (ERK) in BRAF wild-type cells has been implicated in RAF inhibitor-induced cSCC. Here, we report that sorafenib suppresses UV-induced apoptosis specifically by inhibiting c-jun-NH(2)-kinase (JNK) activation through the off-target inhibition of leucine zipper and sterile alpha motif-containing kinase (ZAK). Our results implicate suppression of JNK signaling, independent of the ERK pathway, as an additional mechanism of adverse effects of sorafenib. This has broad implications for combination therapies using sorafenib with other modalities that induce apoptosis.

Predicting protein-protein interactions in the post synaptic density

The post synaptic density (PSD) is a specialization of the cytoskeleton at the synaptic junction, composed of hundreds of different proteins. Characterizing the protein components of the PSD and their interactions can help elucidate the mechanism of long-term changes in synaptic plasticity, which underlie learning and memory. Unfortunately, our knowledge of the proteome and interactome of the PSD is still partial and noisy. In this study we describe a computational framework to improve the reconstruction of the PSD network. The approach is based on learning the characteristics of PSD protein interactions from a set of trusted interactions, expanding this set with data collected from large scale repositories, and then predicting novel interaction with proteins that are suspected to reside in the PSD. Using this method we obtained thirty predicted interactions, with more than half of which having supporting evidence in the literature. We discuss in details two of these new interactions, Lrrtm1 with PSD-95 and Src with Capg. The first may take part in a mechanism underlying glutamatergic dysfunction in schizophrenia. The second suggests an alternative mechanism to regulate dendritic spines maturation.

JNK pathway activation is controlled by Tao/TAOK3 to modulate ethanol sensitivity

Neuronal signal transduction by the JNK MAP kinase pathway is altered by a broad array of stimuli including exposure to the widely abused drug ethanol, but the behavioral relevance and the regulation of JNK signaling is unclear. Here we demonstrate that JNK signaling functions downstream of the Sterile20 kinase family gene tao/Taok3 to regulate the behavioral effects of acute ethanol exposure in both the fruit fly Drosophila and mice. In flies tao is required in neurons to promote sensitivity to the locomotor stimulant effects of acute ethanol exposure and to establish specific brain structures. Reduced expression of key JNK pathway genes substantially rescued the structural and behavioral phenotypes of tao mutants. Decreasing and increasing JNK pathway activity resulted in increased and decreased sensitivity to the locomotor stimulant properties of acute ethanol exposure, respectively. Further, JNK expression in a limited pattern of neurons that included brain regions implicated in ethanol responses was sufficient to restore normal behavior. Mice heterozygous for a disrupted allele of the homologous Taok3 gene (Taok3Gt) were resistant to the acute sedative effects of ethanol. JNK activity was constitutively increased in brains of Taok3Gt/+ mice, and acute induction of phospho-JNK in brain tissue by ethanol was occluded in Taok3Gt/+ mice. Finally, acute administration of a JNK inhibitor conferred resistance to the sedative effects of ethanol in wild-type but not Taok3Gt/+ mice. Taken together, these data support a role of a TAO/TAOK3-JNK neuronal signaling pathway in regulating sensitivity to acute ethanol exposure in flies and in mice.

Germinal center kinases in immune regulation

Germinal center kinases (GCKs) participate in a variety of signaling pathways needed to regulate cellular functions including apoptosis, cell proliferation, polarity and migration. Recent studies have shown that GCKs are participants in both adaptive and innate immune regulation. However, the differential activation and regulatory mechanisms of GCKs, as well as upstream and downstream signaling molecules, remain to be fully defined. It remains unresolved whether and how GCKs may cross-talk with existing signaling pathways. This review stresses the progresses in research of GCKs relevant to the immune system.

Taok2 controls behavioral response to ethanol in mice

Despite recent advances in the understanding of ethanol's biological action, many of the molecular targets of ethanol and mechanisms behind ethanol's effect on behavior remain poorly understood. In an effort to identify novel genes, the products of which regulate behavioral responses to ethanol, we recently identified a mutation in the dtao gene that confers resistance to the locomotor stimulating effect of ethanol in Drosophila. dtao encodes a member of the Ste20 family of serine/threonine kinases implicated in MAP kinase signaling pathways. In this study, we report that conditional ablation of the mouse dtao homolog, Taok2, constitutively and specifically in the nervous system, results in strain-specific and overlapping alterations in ethanol-dependent behaviors. These data suggest a functional conservation of dtao and Taok2 in mediating ethanol's biological action and identify Taok2 as a putative candidate gene for ethanol use disorders in humans.

Autism spectrum disorder susceptibility gene TAOK2 affects basal dendrite formation in the neocortex

How neurons develop their morphology is an important question in neurobiology. Here we describe a new pathway that specifically affects the formation of basal dendrites and axonal projections in cortical pyramidal neurons. We report that thousand-and-one-amino acid 2 kinase (TAOK2), also known as TAO2, is essential for dendrite morphogenesis. TAOK2 downregulation impairs basal dendrite formation in vivo without affecting apical dendrites. Moreover, TAOK2 interacts with Neuropilin 1 (Nrp1), a receptor protein that binds the secreted guidance cue Semaphorin 3A (Sema3A). TAOK2 overexpression restores dendrite formation in cultured cortical neurons from Nrp1(Sema-) mice, which express Nrp1 receptors incapable of binding Sema3A. TAOK2 overexpression also ameliorates the basal dendrite impairment resulting from Nrp1 downregulation in vivo. Finally, Sema3A and TAOK2 modulate the formation of basal dendrites through the activation of the c-Jun N-terminal kinase (JNK). These results delineate a pathway whereby Sema3A and Nrp1 transduce signals through TAOK2 and JNK to regulate basal dendrite development in cortical neurons.

Elevated expression of RGS19 impairs the responsiveness of stress-activated protein kinases to serum

Regulators of G protein signaling (RGS proteins) serve as GTPase activating proteins for the signal transducing Gα subunits. RGS19, also known as Gα-interacting protein (GAIP), has been shown to subserve other functions such as the regulation of macroautophagy and growth factor signaling. We have recently demonstrated that the expression of RGS19 in human embryonic kidney (HEK) 293 cells resulted in the disruption of serum-induced mitogenic response along the classical Ras/Raf/MEK/ERK pathway. Here, we further examined the effect of RGS19 expression on the stress-activated protein kinases (SAPKs). Both c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) became non-responsive to serum in 293/RGS19 cells, yet the two SAPKs responded to UV irradiation or osmotic stress induced by sorbitol. Kinases upstream of JNK and p38 MAPK, including MKK3/6, MKK4, and MLK3, also failed to respond to serum stimulation in 293/RGS19 cells. Serum-induced activation of the small GTPases Rac1 and Cdc42 was similarly suppressed in these cells. Our results indicate that elevated expression of RGS19 can severely disrupt the regulation of MAPKs by small GTPases.

Apoptosis signaling kinases: from stress response to health outcomes

Apoptosis is a highly regulated process essential for the development and homeostasis of multicellular organisms. Whereas caspases, a large family of intracellular cysteine proteases, play central roles in the execution of apoptosis, other proapoptotic and antiapoptotic regulators such as the members of the Bcl-2 family are also critically involved in the regulation of apoptosis. A large body of evidence has revealed that a number of protein kinases are among such regulators and regulate cellular sensitivity to various proapoptotic signals at multiple steps in apoptosis. However, recent progress in the analysis of these apoptosis signaling kinases demonstrates that they generally act as crucial regulators of diverse cellular responses to a wide variety of stressors, beyond their roles in apoptosis regulation. In this review, we have cataloged apoptosis signaling kinases involved in cellular stress responses on the basis of their ability to induce apoptosis and discuss their roles in stress responses with particular emphasis on health outcomes upon their dysregulation.

Arsenic trioxide-dependent activation of thousand-and-one amino acid kinase 2 and transforming growth factor-beta-activated kinase 1

Arsenic trioxide (As(2)O(3)) has potent antileukemic properties in vitro and in vivo, but the mechanisms by which it generates its effects on target leukemic cells are not well understood. Understanding cellular mechanisms and pathways that are activated in leukemic cells to control the generation of As(2)O(3) responses should have important implications in the development of novel approaches using As(2)O(3) for the treatment of leukemias. In this study, we used immunoblotting and immune complex kinase assays to provide evidence that the kinases thousand-and-one amino acid kinase 2 (TAO2) and transforming growth factor-beta-activated kinase 1 (TAK1) are rapidly activated in response to treatment of acute leukemia cells with As(2)O(3). Such activation occurs after the generation of reactive oxygen species and regulates downstream engagement of the p38 mitogen-activated protein kinase. Our studies demonstrate that siRNA-mediated knockdown of TAO2 or TAK1 or pharmacological inhibition of TAK1 enhances the suppressive effects of As(2)O(3) on KT-1-derived leukemic progenitor colony formation and on primary leukemic progenitors from patients with acute myelogenous leukemia. These results indicate key negative-feedback regulatory roles for these kinases in the generation of the antileukemic effects of As(2)O(3). Thus, molecular or pharmacological targeting of these kinases may provide a novel approach to enhance the generation of arsenic-dependent antileukemic responses.

Structural studies of MAP Kinase cascade components

MAPK cascade components have been the subject of structural analysis, advancing our understanding of how these enzymes are activated and how they interact. A surprising finding has been that unique inactive conformers are adopted by many of these kinases. These inactive conformers are interesting and often require experimental phases to determine their crystal structures because molecular replacement techniques are not successful. Here, we describe the preparation of MAP2K MEK6 and MAP3K TAO2 substituted with selenomethionine (SeMet) for de novo phasing. TAO2 and SeMet TAO2 were expressed in insect cells.

The germinal center kinase GCK-1 is a negative regulator of MAP kinase activation and apoptosis in the C. elegans germline

The germinal center kinases (GCK) constitute a large, highly conserved family of proteins that has been implicated in a wide variety of cellular processes including cell growth and proliferation, polarity, migration, and stress responses. Although diverse, these functions have been attributed to an evolutionarily conserved role for GCKs in the activation of ERK, JNK, and p38 MAP kinase pathways. In addition, multiple GCKs from different species promote apoptotic cell death. In contrast to these paradigms, we found that a C. elegans GCK, GCK-1, functions to inhibit MAP kinase activation and apoptosis in the C. elegans germline. In the absence of GCK-1, a specific MAP kinase isoform is ectopically activated and oocytes undergo abnormal development. Moreover, GCK-1- deficient animals display a significant increase in germ cell death. Our results suggest that individual germinal center kinases act in mechanistically distinct ways and that these functions are likely to depend on organ- and developmental-specific contexts.

MAP3Ks as central regulators of cell fate during development

The cytoplasmic serine/threonine kinases transduce extracellular signals into regulatory events that impact cellular responses. The induction of one kinase triggers the activation of several downstream kinases, leading to the regulation of transcription factors to affect gene function. This arrangement allows for the kinase cascade to be amplified, and integrated according to the cellular context. An upstream mitogen or growth factor signal initiates a module of three kinases: a mitogen-activated protein (MAP) kinase kinase kinase (MAPKKK; e.g., Raf) that phosphorylates and activates a MAP kinase kinase (MAPKK; e.g., MEK) and finally activation of MAP kinase (MAPK; e.g., ERK). Thus, this MAP3K-MAP2K-MAPK module represents critical effectors that regulate extracellular stimuli into cellular responses, such as differentiation, proliferation, and apoptosis all of which function during development. There are 21 characterized MAP3Ks that activate known MAP2Ks, and they function in many aspects of developmental biology. This review summarizes known transduction routes linked to each MAP3K and highlights mouse models that provide clues to their physiological functions. This perspective reveals that some of these MAP3K effectors may have redundant functions, and also serve as unique nexus depending on the context of the signaling pathway.

TAO kinases mediate activation of p38 in response to DNA damage

Thousand and one amino acid (TAO) kinases are Ste20p-related MAP kinase kinase kinases (MAP3Ks) that activate p38 MAPK. Here we show that the TAO kinases mediate the activation of p38 in response to various genotoxic stimuli. TAO kinases are activated acutely by ionizing radiation, ultraviolet radiation, and hydroxyurea. Full-length and truncated fragments of dominant negative TAOs inhibit the activation of p38 by DNA damage. Inhibition of TAO expression by siRNA also decreases p38 activation by these agents. Cells in which TAO kinases have been knocked down are less capable of engaging the DNA damage-induced G2/M checkpoint and display increased sensitivity to IR. The DNA damage kinase ataxia telangiectasia mutated (ATM) phosphorylates TAOs in vitro; radiation induces phosphorylation of TAO on a consensus site for phosphorylation by the ATM protein kinase in cells; and TAO and p38 activation is compromised in cells from a patient with ataxia telangiectasia that lack ATM. These findings indicate that TAO kinases are regulators of p38-mediated responses to DNA damage and are intermediates in the activation of p38 by ATM.

Osmotic stress activates the TAK1-JNK pathway while blocking TAK1-mediated NF-kappaB activation: TAO2 regulates TAK1 pathways

Osmotic stress activates MAPKs, including JNK and p38, which play important roles in cellular stress responses. Transforming growth factor-beta-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and can activate JNK and p38. TAK1 can also activate IkappaB kinase (IKK) that leads to degradation of IkappaB and subsequent NF-kappaB activation. We found that TAK1 is essential for osmotic stress-induced activation of JNK but is not an exclusive mediator of p38 activation. Furthermore, we found that although TAK1 was highly activated upon osmotic stress, it could not induce degradation of IkappaB or activation of NF-kappaB. These results suggest that TAK1 activity is somehow modulated to function specifically in osmotic stress signaling, leading to the activation of JNK but not of IKK. To elucidate the mechanism underlying this modulation, we screened for potential TAK1-binding proteins. We found that TAO2 (thousand-and-one amino acid kinase 2) associates with TAK1 and can inhibit TAK1-mediated activation of NF-kappaB but not of JNK. We observed that TAO2 can interfere with the interaction between TAK1 and IKK and thus may regulate TAK1 function. TAK1 is activated by many distinct stimuli, including cytokines and stresses, and regulation by TAO2 may be important to activate specific intracellular signaling pathways that are unique to osmotic stress.

Crystal structure of the MAP3K TAO2 kinase domain bound by an inhibitor staurosporine

Mitogen-activated protein kinase (MAPK) signal transduction pathways are ubiquitous in eukaryotic cells, which transfer signals from the cell surface to the nucleus, controlling multiple cellular programs. MAPKs are activated by MAPK kinases [MAP2Ks or MAP/extracellular signal-regulated kinase (ERK) kinases (MEK)], which in turn are activated by MAPK kinase kinases (MAP3Ks). TAO2 is a MAP3K level kinase that activates the MAP2Ks MEK3 and MEK6 to activate p38 MAPKs. Because p38 MAPKs are key regulators of expression of inflammatory cytokines, they appear to be involved in human diseases such as asthma and autoimmunity. As an upstream activator of p38s, TAO2 represents a potential drug target. Here we report the crystal structure of active TAO2 kinase domain in complex with staurosporine, a broad-range protein kinase inhibitor that inhibits TAO2 with an IC50 of 3 mM. The structure reveals that staurosporine occupies the position where the adenosine of ATP binds in TAO2, and the binding of the inhibitor mimics many features of ATP binding. Both polar and nonpolar interactions contribute to the enzyme-inhibitor recognition. Staurosporine induces conformational changes in TAO2 residues that surround the inhibitor molecule, but causes very limited global changes in the kinase. The structure provides atomic details for TAO2-staurosporine interactions, and explains the relatively low potency of staurosporine against TAO2. The structure presented here should aid in the design of inhibitors specific to TAO2 and related kinases.

Prostate-derived sterile 20-like kinase 2 (PSK2) regulates apoptotic morphology via C-Jun N-terminal kinase and Rho kinase-1

We have reported previously that human prostate-derived sterile 20-like kinase (PSK) 1 alters actin cytoskeletal organization and binds to microtubules, regulating their organization and stability. We have shown a structurally related protein kinase PSK2, which lacks a microtubule-binding site, activated c-Jun N-terminal kinase (JNK), and induced apoptotic morphological changes that include cell contraction, membrane blebbing, and apoptotic body formation. Apoptotic stimuli increased the catalytic activity of endogenous PSK2 and JNK, and dominant negative JNK or a physiological inhibitor of JNK blocked these apoptotic morphological responses to PSK2, demonstrating a requirement for JNK. PSK2 also stimulated the cleavage of Rho kinase-1 (ROCK-I), and the activity of ROCK-I was required for PSK2 to induce cell contraction and membrane blebbing. The activation of caspases was also needed for the induction of membrane blebbing by PSK2, which was itself a substrate for caspase 3. PSK2 therefore regulates apoptotic morphology associated with the execution phase of apoptosis, which involves dynamic reorganization of the actin cytoskeleton, via downstream targets that include JNK and ROCK-I. Our findings suggest that PSKs form a subgroup of sterile 20 (STE20)-like kinases that regulate different cytoskeletal processes.

Conserved Docking Site Is Essential for Activation of Mammalian MAP Kinase Kinases by Specific MAP Kinase Kinase Kinases

Mammalian mitogen-activated protein kinase (MAPK) cascades control various cellular events, ranging from cell growth to apoptosis, in response to external stimuli. A conserved docking site, termed DVD, is found in the mammalian MAP kinase kinases (MAPKKs) belonging to the three major subfamilies, namely MEK1, MKK4/7, and MKK3/6. The DVD sites bind to their specific upstream MAP kinase kinase kinases (MAPKKKs), including MTK1 (MEKK4), ASK1, TAK1, TAO2, MEKK1, and Raf-1. DVD site is a stretch of about 20 amino acids immediately on the C-terminal side of the MAPKK catalytic domain. Mutations in the DVD site strongly inhibited MAPKKs from binding to, and being activated by, their specific MAPKKKs, both in vitro and in vivo. DVD site mutants could not be activated by various external stimuli in vivo. Synthetic DVD oligopeptides inhibited specific MAPKK activation, both in vitro and in vivo, demonstrating the critical importance of the DVD docking in MAPK signaling.

Crystal structure of the TAO2 kinase domain: activation and specificity of a Ste20p MAP3K

TAO2 is a mitogen-activated protein kinase kinase kinase (MAP3K) that doubly phosphorylates and activates the MAP kinase kinases (MAP2Ks) MEK3 and MEK6. The structure of the kinase domain of TAO2 (1-320) has been solved in its phosphorylated active conformation. The structure, together with structure-based mutagenic analysis, reveals that positively charged residues in the substrate binding groove mediate the first step in the dual phosphorylation of MEK6, on the threonine residue in the motif DS*VAKT*I (*denotes phosphorylation site) of MEK6. TAO2 is a Ste20p homolog, and the structure of active TAO2, in comparison with that of low-activity p21-activated protein kinase (PAK1), a Ste20p-related MAP4K, reveals how this group of kinases is activated by phosphorylation. Finally, active TAO2 displays unusual interactions with ATP, involving, in part, a subgroup-specific C-terminal extension of TAO2. The observed interactions may be useful in making specific inhibitors of TAO kinases.

Krox20 stimulates adipogenesis via C/EBPbeta-dependent and -independent mechanisms

Krox20 is a zinc finger-containing transcription factor that is abundantly expressed in adipose tissue. However, its role in fat cell differentiation has not been established. In cultured 3T3-L1 cells, Krox20 is rapidly induced by serum stimulation. Overexpression of Krox20 in both 3T3-L1 preadipocytes and multipotent NIH3T3 cells promotes adipogenesis in a hormone-dependent manner. Conversely, RNAi-mediated loss of Krox20 function reduced adipogenesis in 3T3-L1 cells. Ectopic expression of Krox20 can transactivate the C/EBPbeta promoter and increase C/EBPbeta gene expression in 3T3-L1 preadipocytes. RNAi-mediated knockdown of C/EPBbeta diminished Krox20's proadipogenic effect. Finally, coexpression of Krox20 and C/EBPbeta in naive NIH3T3 cells resulted in the pronounced induction of a fully differentiated adipocyte phenotype, an effect previously observed only with PPARgamma. These data indicate that Krox20 is necessary for adipogenesis and that, when overexpressed, Krox20 potently stimulates adipogenesis via C/EBPbeta-dependent and -independent mechanisms.

WNK1 activates ERK5 by an MEKK2/3-dependent mechanism

WNK1 belongs to a unique protein kinase family that lacks the catalytic lysine in its normal position. Mutations in human WNK1 and WNK4 have been implicated in causing a familial form of hypertension. Here we report that overexpression of WNK1 led to increased activity of cotransfected ERK5 in HEK293 cells. ERK5 activation was blocked by the MEK5 inhibitor U0126 and expression of a dominant negative MEK5 mutant. Expression of dominant negative mutants of MEKK2 and MEKK3 also blocked activation of ERK5 by WNK1. Moreover, both MEKK2 and MEKK3 coimmunoprecipitated with endogenous WNK1 from cell lysates. WNK1 phosphorylated both MEKK2 and -3 in vitro, and MEKK3 was activated by WNK1 in 293 cells. Finally, ERK5 activation by epidermal growth factor was attenuated by suppression of WNK1 expression using small interfering RNA. Taken together, these results place WNK1 in the ERK5 MAP kinase pathway upstream of MEKK2/3.

TAO (thousand-and-one amino acid) protein kinases mediate signaling from carbachol to p38 mitogen-activated protein kinase and ternary complex factors

The TAO (for thousand-and-one amino acids) protein kinases activate p38 mitogen-activated protein (MAP) kinase cascades in vitro and in cells by phosphorylating the MAP/ERK kinases (MEKs) 3 and 6. We found that TAO2 activity was increased by carbachol and that carbachol and the heterotrimeric G protein Galphao could activate p38 in 293 cells. Using dominant interfering kinase mutants, we found that MEKs 3 and 6 and TAOs were required for p38 activation by carbachol or the constitutively active mutant GalphaoQ205L. To explore events downstream of TAOs, the effects of TAO2 on ternary complex factors (TCFs) were investigated. Transfection studies demonstrated that TAO2 stimulates phosphorylation of the TCF Elk1 on the major activating site, Ser383, and that TAO2 stimulates transactivation of Elk1 and the related TCF, Sap1. Reporter activity was reduced by the p38-selective inhibitor SB203580. Taken together, these studies suggest that TAO protein kinases relay signals from carbachol through heterotrimeric G proteins to the p38 MAP kinase, which then activates TCFs in the nucleus.

The prostate-derived sterile 20-like kinase (PSK) regulates microtubule organization and stability

Sterile 20 (STE20) protein kinases, which include germinal center kinases and p21-activated protein kinases, are known to activate mitogen-activated protein kinase pathways (c-Jun NH(2)-terminal kinase, p38, or extracellular signal-regulated kinase), leading to changes in gene transcription. Some STE20s can also regulate the cytoskeleton, and we have shown that the germinal center kinase-like kinase prostate-derived STE20-like kinase (PSK) affects actin cytoskeletal organization. Here, we demonstrate that PSK colocalizes with microtubules; and that this localization is disrupted by the microtubule depolymerizing agent nocodazole. The association of PSK with microtubules results in the production of stabilized perinuclear microtubule cables that are nocodazole-resistant and contain increased levels of acetylated alpha-tubulin. Kinase-defective PSK (K57A) or the C terminus of PSK (amino acids 745-1235) lacking the kinase domain are sufficient for microtubule binding and stabilization, demonstrating that the catalytic activity of the protein is not required. The localization of PSK to microtubules occurs via its C terminus, and PSK binds and phosphorylates alpha- and beta-tubulin in vitro. The N terminus of PSK (1-940) is unable to bind or stabilize microtubules, demonstrating that PSK must associate with microtubules for their reorganization to occur. These results demonstrate that PSK interacts with microtubules and affects their organization and stability independently of PSK kinase activity.

Stimulus-specific requirements for MAP3 kinases in activating the JNK pathway

Mitogen-activated protein kinases (MAPKs) are activated by numerous ligands typically through a protein kinase cascade minimally composed of the MAPK in series with a MAP2 kinase (MAP2K) and a MAP3K. This arrangement is thought to confer specificity and appropriate kinetic properties on the activation of MAPKs in response to physiological stimuli. Surprisingly, more than a dozen MAP3Ks have been identified that activate the c-Jun N-terminal kinases (JNKs) when overexpressed, but there is no clear understanding of which kinases actually mediate JNK activation by ligands. Here, we use double-stranded RNA-mediated interference of gene expression to reveal the explicit participation of discrete MAP3Ks in controlling JNK activity by multiple stimuli. Maximal activation of JNK by lipopolysaccharide requires the MAP3K TAK1. On the other hand, sorbitol requires expression of four MAP3Ks to cause maximal JNK activation. Thus, we demonstrate that specific stimuli use different mechanisms to recruit distinct MAP3Ks to regulate the JNK pathway.