Serine/Threonine kinases 3pK and MAPK-activated protein kinase 2 interact with the basic helix-loop-helix transcription factor E47 and repress its transcriptional activity

Characterization and clustering of kinase isoform expression in metastatic melanoma

Mutations to the human kinome are known to play causal roles in cancer. The kinome regulates numerous cell processes including growth, proliferation, differentiation, and apoptosis. In addition to aberrant expression, aberrant alternative splicing of cancer-driver genes is receiving increased attention as it could lead to loss or gain of functional domains, altering a kinase's downstream impact. The present study quantifies changes in gene expression and isoform ratios in the kinome of metastatic melanoma cells relative to primary tumors. We contrast 538 total kinases and 3,040 known kinase isoforms between 103 primary tumor and 367 metastatic samples from The Cancer Genome Atlas (TCGA). We find strong evidence of differential expression (DE) at the gene level in 123 kinases (23%). Additionally, of the 468 kinases with alternative isoforms, 60 (13%) had significant difference in isoform ratios (DIR). Notably, DE and DIR have little correlation; for instance, although DE highlights enrichment in receptor tyrosine kinases (RTKs), DIR identifies altered splicing in non-receptor tyrosine kinases (nRTKs). Using exon junction mapping, we identify five examples of splicing events favored in metastatic samples. We demonstrate differential apoptosis and protein localization between SLK isoforms in metastatic melanoma. We cluster isoform expression data and identify subgroups that correlate with genomic subtypes and anatomic tumor locations. Notably, distinct DE and DIR patterns separate samples with BRAF hotspot mutations and (N/K/H)RAS hotspot mutations, the latter of which lacks effective kinase inhibitor treatments. DE in RAS mutants concentrates in CMGC kinases (a group including cell cycle and splicing regulators) rather than RTKs as in BRAF mutants. Furthermore, isoforms in the RAS kinase subgroup show enrichment for cancer-related processes such as angiogenesis and cell migration. Our results reveal a new approach to therapeutic target identification and demonstrate how different mutational subtypes may respond differently to treatments highlighting possible new driver events in cancer.

HAND1 loss-of-function within the embryonic myocardium reveals survivable congenital cardiac defects and adult heart failure

AIMS

To examine the role of the basic Helix-loop-Helix (bHLH) transcription factor HAND1 in embryonic and adult myocardium.

METHODS AND RESULTS

Hand1 is expressed within the cardiomyocytes of the left ventricle (LV) and myocardial cuff between embryonic days (E) 9.5-13.5. Hand gene dosage plays an important role in ventricular morphology and the contribution of Hand1 to congenital heart defects requires further interrogation. Conditional ablation of Hand1 was carried out using either Nkx2.5 knockin Cre (Nkx2.5Cre) or α-myosin heavy chain Cre (αMhc-Cre) driver. Interrogation of transcriptome data via ingenuity pathway analysis reveals several gene regulatory pathways disrupted including translation and cardiac hypertrophy-related pathways. Embryo and adult hearts were subjected to histological, functional, and molecular analyses. Myocardial deletion of Hand1 results in morphological defects that include cardiac conduction system defects, survivable interventricular septal defects, and abnormal LV papillary muscles (PMs). Resulting Hand1 conditional mutants are born at Mendelian frequencies; but the morphological alterations acquired during cardiac development result in, the mice developing diastolic heart failure.

CONCLUSION

Collectively, these data reveal that HAND1 contributes to the morphogenic patterning and maturation of cardiomyocytes during embryogenesis and although survivable, indicates a role for Hand1 within the developing conduction system and PM development.

Coupling of Cell Division and Differentiation in Arabidopsis thaliana Cultured Cells with Interaction of Ethylene and ABA Signaling Pathways

Recent studies indicate direct links between molecular cell cycle and cell differentiation machineries. Ethylene and abscisic acid (ABA) are known to affect cell division and differentiation, but the mechanisms of such effects are poorly understood. As ethylene and ABA signaling routes may interact, we examined their involvement in cell division and differentiation in cell tissue cultures derived from several Arabidopsis thaliana plants: wild type (Col-0), and ethylene-insensitive mutants etr1-1, ctr1-1, and ein2-1. We designed an experimental setup to analyze the growth-related parameters and molecular mechanisms in proliferating cells upon short exposure to ABA. Here, we provide evidence for the ethylene-ABA signaling pathways' interaction in the regulation of cell division and differentiation as follows: (1) when the ethylene signal transduction pathway is functionally active (Col-0), the cells actively proliferate, and exogenous ABA performs its function as an inhibitor of DNA synthesis and division; (2) if the ethylene signal is not perceived (etr1-1), then, in addition to cell differentiation (tracheary elements formation), cell death can occur. The addition of exogenous ABA can rescue the cells via increasing proliferation; (3) if the ethylene signal is perceived, but not transduced (ein2-1), then cell differentiation takes place-the latter is enhanced by exogenous ABA while cell proliferation is reduced; (4) when the signal transduction pathway is constitutively active, the cells begin to exit the cell cycle and proceed to endo-reduplication (ctr1-1). In this case, the addition of exogenous ABA promotes reactivation of cell division.

Periovulatory insulin signaling is essential for ovulation, granulosa cell differentiation, and female fertility

Recent studies have demonstrated an essential role for insulin signaling in folliculogenesis as conditional ablation of Igf1r in primary follicles elicits defective follicle-stimulating hormone responsiveness blocking development at the preantral stage. Thus the potential role of insulin action in the periovulatory window and in the corpus luteum is unknown. To examine this, we generated conditional Insr,Igf1r, and double receptor knockout mice driven by Pgr-Cre. These models escape the preantral follicle block and in response to superovulatory gonadotropins exhibit normal distribution of ovarian follicles and corpora lutea. However, single ablation of Igf1r leads to subfertility and mice lacking both receptors are infertile. Double knockout mice have impaired oocyte development and ovulation. While some oocytes are released and fertilized, subsequent embryo development is retarded, and the embryos potentially fail to thrive due to lack of luteal support. In support of this, we found reduced expression of key enzymes in the steroid synthesis pathway and reduced serum progesterone. In addition to metabolic and steroidogenic pathways, RNA-sequencing analysis revealed transcription factor-3 as an important transcription factor downstream of insulin signaling. Collectively, these results highlight the importance of growth factors of the insulin family during two distinct windows of follicular development, ovulation, and luteinization.

Martinique Crinkled Retinal Pigment Epitheliopathy: Clinical Stages and Pathophysiologic Insights

PURPOSE

To reappraise the autosomal dominant Martinique crinkled retinal pigment epitheliopathy (MCRPE) in light of the knowledge of its associated mutated gene mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3), an actor in the p38 mitogen-activated protein kinase pathway.

DESIGN

Clinical and molecular study.

PARTICIPANTS

A total of 45 patients from 3 generations belonging to a family originating from Martinique with an autosomal dominant MCRPE were examined.

METHODS

Best-corrected visual acuity, fundus photographs, and spectral-domain optical coherence tomography (SD OCT) of all clinically affected patients and carriers for the causal mutation were reviewed at the initial visit and 4 years later for 10 of them. Histologic retinal lesions of Mapkapk3(-/-) mice were compared with those of the human disease.

MAIN OUTCOME MEASURES

The MCRPE natural history in view of MAPKAPK3 function and Mapkapk3(-/-) mouse retinal lesions.

RESULTS

Eighteen patients had the c.518T>C mutation. One heterozygous woman aged 20 years was asymptomatic with normal fundus and SD OCT (stage 0). All c.518T>C heterozygous patients older than 30 years of age had the characteristic dried-out soil fundus pattern (stages 1 and 2). Complications (stage 3) were observed in 7 cases, including polypoidal choroidal vasculopathy (PCV) and macular fibrosis or atrophy. One patient was homozygous and had a form with severe Bruch's membrane (BM) thickening and macular exudation with a dried-out soil pattern in the peripheral retina. The oldest heterozygous patient, who was legally blind, had peripheral nummular pigmentary changes (stage 4). After 4 years, visual acuity was unchanged in 6 of 10 patients. The dried-out soil elementary lesions radically enlarged in patients with a preferential macular extension and confluence. These findings are in line with the progressive thickening of BM noted with age in the mouse model. During follow-up, there was no occurrence of PCV.

CONCLUSIONS

MCRPE is an autosomal dominant, fully penetrant retinal dystrophy with a preclinical stage, an onset after the age of 30 years, and a preserved visual acuity until occurrence of macular complications. The natural history of MCRPE is in relation to the role of MAPKAPK3 in BM modeling, vascular endothelial growth factor activity, retinal pigment epithelial responses to aging, and oxidative stress.

A dominant mutation in MAPKAPK3, an actor of p38 signaling pathway, causes a new retinal dystrophy involving Bruch's membrane and retinal pigment epithelium

Inherited retinal dystrophies are clinically and genetically heterogeneous with significant number of cases remaining genetically unresolved. We studied a large family from the West Indies islands with a peculiar retinal disease, the Martinique crinkled retinal pigment epitheliopathy that begins around the age of 30 with retinal pigment epithelium (RPE) and Bruch's membrane changes resembling a dry desert land and ends with a retinitis pigmentosa. Whole-exome sequencing identified a heterozygous c.518T>C (p.Leu173Pro) mutation in MAPKAPK3 that segregates with the disease in 14 affected and 28 unaffected siblings from three generations. This unknown variant is predicted to be damaging by bioinformatic predictive tools and the mutated protein to be non-functional by crystal structure analysis. MAPKAPK3 is a serine/threonine protein kinase of the p38 signaling pathway that is activated by a variety of stress stimuli and is implicated in cellular responses and gene regulation. In contrast to other tissues, MAPKAPK3 is highly expressed in the RPE, suggesting a crucial role for retinal physiology. Expression of the mutated allele in HEK cells revealed a mislocalization of the protein in the cytoplasm, leading to cytoskeleton alteration and cytodieresis inhibition. In Mapkapk3-/- mice, Bruch's membrane is irregular with both abnormal thickened and thinned portions. In conclusion, we identified the first pathogenic mutation in MAPKAPK3 associated with a retinal disease. These findings shed new lights on Bruch's membrane/RPE pathophysiology and will open studies of this signaling pathway in diseases with RPE and Bruch's membrane alterations, such as age-related macular degeneration.

Nuclear phosphoproteome of developing chickpea seedlings (Cicer arietinum L.) and protein-kinase interaction network

Nucleus, the control centre of eukaryotic cell, houses most of the genetic machineries required for gene expression and their regulation. Post translational modifications of proteins, particularly phosphorylation control a wide variety of cellular processes but its functional connectivity, in plants, is still elusive. This study profiled the nuclear phosphoproteome of a grain legume, chickpea, to gain better understanding of such event. Intact nuclei were isolated from 3-week-old seedlings using two independent methods, and nuclear proteins were resolved by 2-DE. In a separate set of experiments, phosphoproteins were enriched using IMAC method and resolved by 1-DE. The separated proteins were stained with phosphospecific Pro-Q Diamond stain. Proteomic analyses led to the identification of 107 putative phosphoproteins, of which 86 were non-redundant. Multiple sites of phosphorylation were predicted on several key elements, which included both regulatory and functional proteins. The analysis revealed an array of phosphoproteins, presumably involved in a variety of cellular functions, viz., protein folding (24%), signalling and gene regulation (22%), DNA replication, repair and modification (16%), and metabolism (13%), among others. These results represent the first nucleus-specific phosphoproteome map of a non-model legume, which would provide insights into the possible function of protein phosphorylation in plants.

BIOLOGICAL SIGNIFICANCE

Chickpea is grown over 10 million hectares of land worldwide, and global production hovers around 8.5 million metric tons annually. Despite its nutritional merits, it is often referred to as 'orphan' legume and has remained outside the realm of large-scale functional genomics studies. While current chickpea genome initiative has primarily focused on sequence information and functional annotation, proteomics analyses are limited. It is thus important to study the proteome of the cell organelle particularly the nucleus, which harbors most of the genetic information and gene expression machinery. Phosphorylation-dependent modulation of gene expression plays a vital role but the complex networks of phosphorylation are poorly understood. This inventory of nuclear phosphoproteins would provide valuable insights into the dynamic regulation of cellular phenotype through phosphorylation. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Functional redundancy between the transcriptional activation domains of E2A is mediated by binding to the KIX domain of CBP/p300

The E-protein transcription factors play essential roles in lymphopoiesis, with E12 and E47 (hereafter called E2A) being particularly important in B cell specification and maturation. The E2A gene is also involved in a chromosomal translocation that results in the leukemogenic oncoprotein E2A-PBX1. The two activation domains of E2A, AD1 and AD2, display redundant, independent, and cooperative functions in a cell-dependent manner. AD1 of E2A functions by binding the transcriptional co-activator CBP/p300; this interaction is required in oncogenesis and occurs between the conserved ϕ-x-x-ϕ-ϕ motif in AD1 and the KIX domain of CBP/p300. However, co-activator recruitment by AD2 has not been characterized. Here, we demonstrate that the first of two conserved ϕ-x-x-ϕ-ϕ motifs within AD2 of E2A interacts at the same binding site on KIX as AD1. Mutagenesis uncovered a correspondence between the KIX-binding affinity of AD2 and transcriptional activation. Although AD2 is dispensable for oncogenesis, experimentally increasing the affinity of AD2 for KIX uncovered a latent potential to mediate immortalization of primary hematopoietic progenitors by E2A-PBX1. Our findings suggest that redundancy between the two E2A activation domains with respect to transcriptional activation and oncogenic function is mediated by binding to the same surface of the KIX domain of CBP/p300.

Activation and function of the MAPKs and their substrates, the MAPK-activated protein kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

Activation and Function of the MAPKs and Their Substrates, the MAPK-Activated Protein Kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

Identification of RANBP16 and RANBP17 as novel interaction partners for the bHLH transcription factor E12

The ubiquitously expressed basic helix-loop-helix (bHLH) transcription factors E12 and E47, products of alternative splicing of the E2A/TCF3 gene, regulate diverse biological processes including cell growth, differentiation and development. To search for novel protein interactions for E12, we utilized the bHLH domain of E12 as a bait in yeast two-hybrid screening. Yeast two-hybrid, mammalian two-hybrid, and co-immunoprecipitation analyses demonstrate specific interaction of E12 with RANBP17, a novel member of the importin-beta superfamily; this interaction maps to the CRM1 homology region of RANBP17. Ectopic expression of RANBP17 leads to a approximately 3-fold increase in E2A/MyoD mediated transactivation of an E-box regulated luciferase reporter gene. Interaction and transactivation studies also revealed similar functions for RANBP16/XPO7. Furthermore, ectopic expression of either RANBP16 or RANBP17 resulted in increased level of endogenous transcript for the cyclin-dependent kinase inhibitor, p21(Waf1/Cip1), a well-characterized E2A target gene. Together, these biochemical and functional data reveal RANBP16 and RANBP17 as novel regulators of E2A protein action.

Characterization of a novel MK3 splice variant from murine ventricular myocardium

p38 MAP kinase (MAPK) isoforms alpha, beta, and gamma, are expressed in the heart. p38alpha appears pro-apoptotic whereas p38beta is pro-hypertrophic. The mechanisms mediating these divergent effects are unknown; hence elucidating the downstream signaling of p38 should further our understanding. Downstream effectors include MAPK-activated protein kinase (MK)-3, which is expressed in many tissues including skeletal muscles and heart. We cloned full-length MK3 (MK3.1, 384 aa) and a novel splice variant (MK3.2, 266 aa) from murine heart. For MK3.2, skipping of exons 8 and 9 resulted in a frame-shift in translation of the first 85 base pairs of exon 10 followed by an in-frame stop codon. Of 3 putative phosphorylation sites for p38 MAPK, only Thr-203 remained functional in MK3.2. In addition, MK3.2 lacked nuclear localization and export signals. Quantitative real-time PCR confirmed the presence of these mRNA species in heart and skeletal muscle; however, the relative abundance of MK3.2 differed. Furthermore, whereas total MK3 mRNA was increased, the relative abundance of MK3.2 mRNA decreased in MK2(-/-) mice. Immunoblotting revealed 2 bands of MK3 immunoreactivity in ventricular lysates. Ectopically expressed MK3.1 localized to the nucleus whereas MK3.2 was distributed throughout the cell; however, whereas MK3.1 translocated to the cytoplasm in response to osmotic stress, MK3.2 was degraded. The p38alpha/beta inhibitor SB203580 prevented the degradation of MK3.2. Furthermore, replacing Thr-203 with alanine prevented the loss of MK3.2 following osmotic stress, as did pretreatment with the proteosome inhibitor MG132. In vitro, GST-MK3.1 was strongly phosphorylated by p38alpha and p38beta, but a poor substrate for p38delta and p38gamma. GST-MK3.2 was poorly phosphorylated by p38alpha and p38beta and not phosphorylated by p38delta and p38gamma. Hence, differential regulation of MKs may, in part, explain diverse downstream effects mediated by p38 signaling.

Mixed lineage kinase phosphorylates transcription factor E47 and inhibits TrkB expression to link neuronal death and survival pathways

E47 is a basic helix-loop-helix transcription factor involved in neuronal differentiation and survival. We had previously shown that the basic helix-loop-helix protein E47 binds to E-box sequences within the promoter of the TrkB gene and activates its transcription. Proper expression of the TrkB receptor plays a key role in development and function of the vertebrate nervous system, and altered levels of TrkB have been associated with important human diseases. Here we show that E47 interacts with MLK2, a mixed lineage kinase (MLK) involved in JNK-mediated activation of programmed cell death. MLK2 enhances phosphorylation of the AD2 activation domain of E47 in vivo in a JNK-independent manner and phosphorylates in vitro defined serine and threonine residues within a loop-helix structure of AD2 that also contains a putative MLK docking site. Although these residues are essential for MLK2-mediated inactivation of E47, inhibition of MLKs by CEP11004 causes up-regulation of TrkB at a transcriptional level in cerebellar granule neurons and differentiating neuroblastoma cells. These findings allow us to propose a novel mechanism by which MLK regulates TrkB expression through phosphorylation of an activation domain of E47. This molecular link would explain why MLK inhibitors not only prevent activation of cell death processes but also enhance cell survival signaling as a key aspect of their neuroprotective potential.

A polymorphism in MAPKAPK3 affects response to interferon therapy for chronic hepatitis C

BACKGROUND & AIMS

This study aimed to identify host single nucleotide polymorphisms (SNPs) that are associated with the efficacy of interferon (IFN) therapy in patients with chronic hepatitis C.

METHODS

We examined whether 116 tagging-SNPs from 13 genes that are involved in type I IFN signaling associate with the outcome of IFN therapy in Japanese case-control groups; the study included 468 sustained responders and 587 nonresponders.

RESULTS

We identified 2 SNPs (rs3792323 [A/T] and rs616589 [G/A]), located in intron 2 of mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3) that were associated with the outcome of IFN therapy in patients infected with hepatitis C virus (HCV) genotype 1b (P = 4.6 x 10(-5) and 4.8 x 10(-5), respectively). The 2 SNPs were in strong linkage disequilibrium and multivariate logistic regression analysis showed that rs3792323 is an independent factor associated with the IFN efficacy (genotype 1b; P = .0011). MAPKAPK3 is a kinase involved in the mitogen and stress responses, but the biological significance of MAPKAPK3 in IFN responses is poorly understood. By using an allele-specific transcript quantification assay in liver biopsy, we showed that allele-specific expression of MAPKAPK3 messenger RNA, corresponding to the risk allele for nonresponse, was significantly higher than that of the other allele. Luciferase reporter assay data indicated that overexpression of MAPKAPK3 inhibits IFN-alfa-induced gene transcription via IFN-stimulated response element and IFN-gamma-activated site.

CONCLUSIONS

The SNP rs3792323 in MAPKAPK3 associates with the outcome of IFN therapy in patients with HCV genotype 1b. Our functional analyses indicate that MAPKAPK3 inhibits IFN-alfa-induced antiviral activity.

E2A proteins promote development of lymphoid-primed multipotent progenitors

The first lymphoid-restricted progeny of hematopoietic stem cells (HSCs) are lymphoid-primed multipotent progenitors (LMPPs), which have little erythromyeloid potential but retain lymphoid, granulocyte, and macrophage differentiation capacity. Despite recent advances in the identification of LMPPs, the transcription factors essential for their generation remain to be identified. Here, we demonstrated that the E2A transcription factors were required for proper development of LMPPs. Within HSCs and LMPPs, E2A proteins primed expression of a subset of lymphoid-associated genes and prevented expression of genes that are not normally prevalent in these cells, including HSC-associated and nonlymphoid genes. E2A proteins also restricted proliferation of HSCs, MPPs, and LMPPs and antagonized differentiation of LMPPs toward the myeloid fate. Our results reveal that E2A proteins play a critical role in supporting lymphoid specification from HSCs and that the reduced generation of LMPPs underlies the severe lymphocyte deficiencies observed in E2A-deficient mice.

Modulation of F-actin rearrangement by the cyclic AMP/cAMP-dependent protein kinase (PKA) pathway is mediated by MAPK-activated protein kinase 5 and requires PKA-induced nuclear export of MK5

The MAPK-activated protein kinases belong to the Ca2+/calmodulin-dependent protein kinases. Within this group, MK2, MK3, and MK5 constitute three structurally related enzymes with distinct functions. Few genuine substrates for MK5 have been identified, and the only known biological role is in ras-induced senescence and in tumor suppression. Here we demonstrate that activation of cAMP-dependent protein kinase (PKA) or ectopic expression of the catalytic subunit Calpha in PC12 cells results in transient nuclear export of MK5, which requires the kinase activity of both Calpha and MK5 and the ability of Calpha to enter the nucleus. Calpha and MK5, but not MK2, interact in vivo, and Calpha increases the kinase activity of MK5. Moreover, Calpha augments MK5 phosphorylation, but not MK2, whereas MK5 does not seem to phosphorylate Calpha. Activation of PKA can induce actin filament accumulation at the plasma membrane and formation of actin-based filopodia. We demonstrate that small interfering RNA-triggered depletion of MK5 interferes with PKA-induced F-actin rearrangement. Moreover, cytoplasmic expression of an activated MK5 variant is sufficient to mimic PKA-provoked F-actin remodeling. Our results describe a novel interaction between the PKA pathway and MAPK signaling cascades and suggest that MK5, but not MK2, is implicated in PKA-induced microfilament rearrangement.

Snail, Zeb and bHLH factors in tumour progression: an alliance against the epithelial phenotype?

The molecular mechanisms that underlie tumour progression are still poorly understood, but recently our knowledge of particular aspects of some of these processes has increased. Specifically, the identification of Snail, ZEB and some basic helix-loop-helix (bHLH) factors as inducers of epithelial-mesenchymal transition (EMT) and potent repressors of E-cadherin expression has opened new avenues of research with potential clinical implications.

The mitogen-activated protein kinase (MAPK)-activated protein kinases MK2 and MK3 cooperate in stimulation of tumor necrosis factor biosynthesis and stabilization of p38 MAPK

MK2 and MK3 represent protein kinases downstream of p38 mitogen-activated protein kinase (MAPK). Deletion of the MK2 gene in mice resulted in an impaired inflammatory response although MK3, which displays extensive structural similarities and identical functional properties in vitro, is still present. Here, we analyze tumor necrosis factor (TNF) production and expression of p38 MAPK and tristetraprolin (TTP) in MK3-deficient mice and demonstrate that there are no significant differences with wild-type animals. We show that in vivo MK2 and MK3 are expressed and activated in parallel. However, the level of activity of MK2 is always significantly higher than that of MK3. Accordingly, we hypothesized that MK3 could have significant effects only in an MK2-free background and generated MK2/MK3 double-knockout mice. Unexpectedly, these mice are viable and show no obvious defects due to loss of compensation between MK2 and MK3. However, there is a further reduction of TNF production and expression of p38 and TTP in double-knockout mice compared to MK2-deficient mice. This finding, together with the observation that ectopically expressed MK3 can rescue MK2 deficiency similarly to MK2, indicates that both kinases share the same physiological function in vivo but are expressed to different levels.

Treatment of neurodegenerative diseases using adult bone marrow stromal cell-derived neurons

Many neurodegenerative diseases are attributed to the degeneration of neurons with subsequent functional loss. Cell transplantation is a strategy with potential for treating such diseases, and many kinds of cells are considered candidates for transplantation therapy. Bone marrow stromal cells (MSCs) have great potential as therapeutic agents, as they are easy to isolate and expand from patients without serious ethical and technical problems. The authors have found a method for the highly efficient, exclusive and specific induction of functional postmitotic neuronal cells from both rat and human MSCs. Gene transfer of Notch intracellular domain (NICD) followed by the administration of certain trophic factors induced mature neurons expressing neuronal markers, some of which showed action potentials. Induced neurons were transplanted to animal models of neurodegenerative disorders, including Parkinson's disease and ischaemic brain injury, resulting in the successful integration of transplanted cells and improvement in function of the transplanted animals. This review summarises the respective potentials, benefits and drawbacks of MSC-derived neurons, and discusses the possibility of their clinical application in neurodegenerative diseases.

MAPKAP kinases - MKs - two's company, three's a crowd

Downstream of mitogen-activated protein kinases (MAPKs), three structurally related MAPK-activated protein kinases (MAPKAPKs or MKs) - MK2, MK3 and MK5 - signal to diverse cellular targets. Although there is no known common function for all three MKs, these kinases are involved in important processes: MKs regulate gene expression at the transcriptional and post-transcriptional level, control cytoskeletal architecture and cell-cycle progression, and are implicated in inflammation and cancer.

MAP kinases as structural adaptors and enzymatic activators in transcription complexes

Mitogen-activated protein kinase (MAPK) pathways regulate eukaryotic gene expression in response to extracellular stimuli. MAPKs and their downstream kinases phosphorylate transcription factors, co-regulators and chromatin proteins to initiate transcriptional changes. However, the spatial context in which the MAPKs operate in transcription complexes is poorly understood. Recent findings in budding yeast show that MAPKs can form integral components of transcription complexes and have novel structural functions in addition to phosphorylating local substrates. Hog1p MAPK is stably recruited to target promoters by specific transcription factors in response to osmotic stress, and acts as both a structural adaptor and enzymatic activator driving the assembly and activation of the transcription complex. We review the evidence that suggests a similar bifunctional role for MAPKs in mammalian transcription complexes.

MAPKAP Kinase 3pK Phosphorylates and Regulates Chromatin Association of the Polycomb Group Protein Bmi1

Polycomb group (PcG) proteins form chromatin-associated, transcriptionally repressive complexes, which are critically involved in the control of cell proliferation and differentiation. Although the mechanisms involved in PcG-mediated repression are beginning to unravel, little is known about the regulation of PcG function. We showed previously that PcG complexes are phosphorylated in vivo, which regulates their association with chromatin. The nature of the responsible PcG kinases remained unknown. Here we present the novel finding that the PcG protein Bmi1 is phosphorylated by 3pK (MAPKAP kinase 3), a convergence point downstream of activated ERK and p38 signaling pathways and implicated in differentiation and developmental processes. We identified 3pK as an interaction partner of PcG proteins, in vitro and in vivo, by yeast two-hybrid interaction and co-immunoprecipitation, respectively. Activation or overexpression of 3pK resulted in phosphorylation of Bmi1 and other PcG members and their dissociation from chromatin. Phosphorylation and subsequent chromatin dissociation of PcG complexes were expected to result in de-repression of targets. One such reported Bmi1 target is the Cdkn2a/INK4A locus. Cells overexpressing 3pK showed PcG complex/chromatin dissociation and concomitant de-repression of p14(ARF), which was encoded by the Cdkn2a/INK4A locus. Thus, 3pK is a candidate regulator of phosphorylation-dependent PcG/chromatin interaction. We speculate that phosphorylation may not only affect chromatin association but, in addition, the function of individual complex members. Our findings linked for the first time MAPK signaling pathways to the Polycomb transcriptional memory system. This suggests a novel mechanism by which a silenced gene status can be modulated and implicates PcG-mediated repression as a dynamically controlled process.

MAPKAP kinase-2 is a primary response gene induced by depolarization in PC12 cells and in brain

Using a combination of targeted differential display for induced protein kinases and differential library screening, we identified mitogen-activated protein kinase activated protein kinase 2 (MAPKAPK2), as a primary response gene whose transcription is stimulated by membrane depolarization and by forskolin in rat PC12 pheochromocytoma cells. MAPKAPK3 was neither induced nor repressed by similar treatments. The increase in MAPKAPK2 mRNA is preceded by an increase in a MAPKAPK2 intron-containing RNA precursor, indicating that the increase in message is due at least in part to increased transcription. The open reading frame of full-length rat MAPKAPK2 cDNA is 99% identical to mouse MAPKAPK2 and 92% identical to human MAPKAPK2. The human MAPKAPK2 predicted protein contains 14 additional amino acids in the proline-rich N-terminal domain, when compared to murine and rat MAPKAPK2 predicted proteins. The MAPKAPK2 form found in PC12 cells corresponds to variant 2 in the human; this ortholog carries a nuclear translocation signal near its C-terminus. MAPKAPK2 message is also induced in the dentate gyrus, CA1, and CA3 of the rat hippocampus between 2-4 hr after the onset of kainic acid-induced seizures.

Immunocytochemical localization of MAPKAPK-2 and Hsp25 in the rat temporomandibular joint

One series of our research has shown an intense expression of immunoreaction for heat shock protein 25 (Hsp25) in various cellular elements in the rat temporomandibular joint (TMJ). This protein is the major substrate of mitogen-activated protein kinase-activated protein kinase-2 (MAPKAPK-2), which mediates an intracellular stress-activated signaling pathway to stimulate cytosolic actin reorganization under various stresses. The present study was undertaken to examine the localization of MAPKAPK-2 in the rat TMJ by immunocytochemical techniques. Furthermore, confocal microscopy with double staining was employed to demonstrate the colocalization of MAPKAPK-2 and Hsp25. Immunocytochemistry for MAPKAPK-2 showed an intense immunoreaction in the cytoplasm of the synovial lining cells, the endothelial cells, and the fibroblasts in the synovial membrane of the rat TMJ. Double immunostaining under a confocal microscope succeeded in demonstrating the colocalization of MAPKAPK-2 and Hsp25 immunoreactions in the cytoplasm of fibroblastic type B synoviocytes in the TMJ. On the other hand, the macrophage-like type A-cells expressed MAPKAPK-2 immunoreactions but lacked Hsp25 immunoreactivity. The cells in the articular disk and the chondrocytes in the maturative and hypertrophic layer of the mandibular cartilage also showed intense immunoreactions for MAPKAPK-2 and Hsp25. In addition to cytoplasmic localization, MAPKAPK-2 immunoreactions were found in the nucleus of some synovial lining cells, cells in the articular disk, and chondrocytes. Current observations imply the presence of the phosphorylation of Hsp25 via activated MAPKAPK-2 in the cytoplasm. MAPKAPK-2 and Hsp25 possibly participate in the induction of cytoskeletal changes to the various cellular elements in rat TMJ under normal conditions.

Mitogen-activated 3p kinase is active in the nucleus

The MAPK-activated kinase 3pK (chromosome 3p kinase), also known as MAPKAPK-3, is a member of a family of kinases that are activated by more than one mitogen-activated protein kinase (MAPK). 3pK is unique since it was shown to be activated by three members of the MAPK family, namely extracellular-signal-regulated kinase (ERK), p38, and Jun-N-terminal kinase (JNK). Accordingly, 3pK is highly activated both by mitogens and by stress-inducing agents or proinflammatory cytokines. Studies utilizing dominant interfering mutants and pharmacological agents revealed that upon mitogenic stimulation, 3pK is exclusively activated via the classical MAPK cascade, while stress-induced activation of 3pK is mainly mediated by p38. The mechanism defining the specificity of kinase action in response to mitogenic versus stress activation remains unknown. Here we show that 3pK is transported to the cytoplasm upon both stress and mitogenic stimulation. While kinetics of nuclear export are similar in both situations, the activation pattern differs substantially. In the mitogenic situation, active 3pK remains in the nucleus for a significant time and there may fulfill mitogen-specific functions. These data not only show that nuclear export of the kinase is mechanistically uncoupled from its activation, but also provide a novel mechanism by which cells may modulate enzyme activity toward a stimulus-specific response.

Specific induction of neuronal cells from bone marrow stromal cells and application for autologous transplantation

Bone marrow stromal cells (MSCs) have the capability under specific conditions of differentiating into various cell types such as osteocytes, chondrocytes, and adipocytes. Here we demonstrate a highly efficient and specific induction of cells with neuronal characteristics, without glial differentiation, from both rat and human MSCs using gene transfection with Notch intracellular domain (NICD) and subsequent treatment with bFGF, forskolin, and ciliary neurotrophic factor. MSCs expressed markers related to neural stem cells after transfection with NICD, and subsequent trophic factor administration induced neuronal cells. Some of them showed voltage-gated fast sodium and delayed rectifier potassium currents and action potentials compatible with characteristics of functional neurons. Further treatment of the induced neuronal cells with glial cell line-derived neurotrophic factor (GDNF) increased the proportion of tyrosine hydroxylase-positive and dopamine-producing cells. Transplantation of these GDNF-treated cells showed improvement in apomorphine-induced rotational behavior and adjusting step and paw-reaching tests following intrastriatal implantation in a 6-hydroxy dopamine rat model of Parkinson disease. This study shows that a population of neuronal cells can be specifically generated from MSCs and that induced cells may allow for a neuroreconstructive approach.

Specific induction of neuronal cells from bone marrow stromal cells and application for autologous transplantation

Bone marrow stromal cells (MSCs) have the capability under specific conditions of differentiating into various cell types such as osteocytes, chondrocytes, and adipocytes. Here we demonstrate a highly efficient and specific induction of cells with neuronal characteristics, without glial differentiation, from both rat and human MSCs using gene transfection with Notch intracellular domain (NICD) and subsequent treatment with bFGF, forskolin, and ciliary neurotrophic factor. MSCs expressed markers related to neural stem cells after transfection with NICD, and subsequent trophic factor administration induced neuronal cells. Some of them showed voltage-gated fast sodium and delayed rectifier potassium currents and action potentials compatible with characteristics of functional neurons. Further treatment of the induced neuronal cells with glial cell line-derived neurotrophic factor (GDNF) increased the proportion of tyrosine hydroxylase-positive and dopamine-producing cells. Transplantation of these GDNF-treated cells showed improvement in apomorphine-induced rotational behavior and adjusting step and paw-reaching tests following intrastriatal implantation in a 6-hydroxy dopamine rat model of Parkinson disease. This study shows that a population of neuronal cells can be specifically generated from MSCs and that induced cells may allow for a neuroreconstructive approach.

ERK and p38 MAPK-activated protein kinases: a family of protein kinases with diverse biological functions

Conserved signaling pathways that activate the mitogen-activated protein kinases (MAPKs) are involved in relaying extracellular stimulations to intracellular responses. The MAPKs coordinately regulate cell proliferation, differentiation, motility, and survival, which are functions also known to be mediated by members of a growing family of MAPK-activated protein kinases (MKs; formerly known as MAPKAP kinases). The MKs are related serine/threonine kinases that respond to mitogenic and stress stimuli through proline-directed phosphorylation and activation of the kinase domain by extracellular signal-regulated kinases 1 and 2 and p38 MAPKs. There are currently 11 vertebrate MKs in five subfamilies based on primary sequence homology: the ribosomal S6 kinases, the mitogen- and stress-activated kinases, the MAPK-interacting kinases, MAPK-activated protein kinases 2 and 3, and MK5. In the last 5 years, several MK substrates have been identified, which has helped tremendously to identify the biological role of the members of this family. Together with data from the study of MK-knockout mice, the identities of the MK substrates indicate that they play important roles in diverse biological processes, including mRNA translation, cell proliferation and survival, and the nuclear genomic response to mitogens and cellular stresses. In this article, we review the existing data on the MKs and discuss their physiological functions based on recent discoveries.

P66ShcAinteracts with MAPKAP kinase 2 and regulates its activity

Three mitogen activated protein kinase-activated protein kinase 2 (MAPKAP kinase 2, MK2) interacting proteins were identified using a yeast two-hybrid approach. ShcA, a signaling phospho-protein, human polyhomeotic 2 (HPH2), a transcriptional regulator, and highly similar to smoothelin (HSTS), which is related to the cytoskeletal associated protein smoothelin, interact specifically with MK2. The interaction of MK2 with the 66 kDa isoform of ShcA, p66(ShcA), and HPH2 was confirmed using co-immunoprecipitation. MK2 is activated with p66(ShcA) co-expression and p66(ShcA) is an in vitro substrate for MK2, further demonstrating their association and suggesting a biological role for p66(Shc) in MK2 activation.

Elimination of protein kinase MK5/PRAK activity by targeted homologous recombination

MK5 (mitogen-activated protein kinase [MAPK]-activated protein kinase 5), also designated PRAK (p38-regulated and -activated kinase), was deleted from mice by homologous recombination. Although no MK5 full-length protein and kinase activity was detected in the MK5 knockout mice, the animals were viable and fertile and did not display abnormalities in tissue morphology or behavior. In addition, these mice did not show increased resistance to endotoxic shock or decreased lipopolysaccharide-induced cytokine production. Hence, MK5 deletion resulted in a phenotype very different from the complex inflammation-impaired phenotype of mice deficient in MK2, although MK2 and MK5 exhibit evolutional, structural, and apparent extensive functional similarities. To explain this discrepancy, we used wild-type cells and embryonic fibroblasts from both MK2 and MK5 knockout mice as controls to reexamine the mechanism of activation, the interaction with endogenous p38 MAPK, and the substrate specificity of both enzymes. In contrast to MK2, which shows interaction with and chaperoning properties for p38 MAPK and which is activated by extracellular stresses such as arsenite or sorbitol treatment, endogenous MK5 did not show these properties. Furthermore, endogenous MK5 is not able to phosphorylate Hsp27 in vitro and in vivo. We conclude that the differences between the phenotypes of MK5- and MK2-deficient mice result from clearly different functional properties of both enzymes.

Transcriptional regulation by the MAP kinase signaling cascades

A major function of the mitogen-activated protein kinase (MAPK) pathways is to control eukaryotic gene expression programmes in response to extracellular signals. MAPKs directly control gene expression by phosphorylating transcription factors. However, it is becoming clear that transcriptional regulation in response to MAPK signaling is more complex. MAPKs can also target coactivators and corepressors and affect nucleosomal structure by inducing histone modifications. Furthermore, multiple inputs into individual promoters can be elicited by MAPKs by targeting different components of the same coregulatory complex or by triggering different events on the same transcription factor. "Postgenomic approaches" are beginning to impact on our understanding of these gene regulatory networks. In this review, we summarise the current knowledge of MAPK-mediated gene regulation, and focus on how complexities in signaling outcomes are achieved and how this relates to physiological processes.

Elimination of protein kinase MK5/PRAK activity by targeted homologous recombination

MK5 (mitogen-activated protein kinase [MAPK]-activated protein kinase 5), also designated PRAK (p38-regulated and -activated kinase), was deleted from mice by homologous recombination. Although no MK5 full-length protein and kinase activity was detected in the MK5 knockout mice, the animals were viable and fertile and did not display abnormalities in tissue morphology or behavior. In addition, these mice did not show increased resistance to endotoxic shock or decreased lipopolysaccharide-induced cytokine production. Hence, MK5 deletion resulted in a phenotype very different from the complex inflammation-impaired phenotype of mice deficient in MK2, although MK2 and MK5 exhibit evolutional, structural, and apparent extensive functional similarities. To explain this discrepancy, we used wild-type cells and embryonic fibroblasts from both MK2 and MK5 knockout mice as controls to reexamine the mechanism of activation, the interaction with endogenous p38 MAPK, and the substrate specificity of both enzymes. In contrast to MK2, which shows interaction with and chaperoning properties for p38 MAPK and which is activated by extracellular stresses such as arsenite or sorbitol treatment, endogenous MK5 did not show these properties. Furthermore, endogenous MK5 is not able to phosphorylate Hsp27 in vitro and in vivo. We conclude that the differences between the phenotypes of MK5- and MK2-deficient mice result from clearly different functional properties of both enzymes.

Mirk/dyrk1B is a Rho-induced kinase active in skeletal muscle differentiation

The Rho family of small GTPases regulates numerous signaling pathways that control the organization of the cytoskeleton, transcription factor activity, and many aspects of the differentiation of skeletal myoblasts. We now demonstrate that the kinase Mirk (minibrain-related kinase)/dyrk1B is induced by members of the Rho-family in myoblasts and that Mirk is active in skeletal muscle differentiation. Mirk is an arginine-directed serine/threonine kinase which is expressed at elevated levels in skeletal muscle compared with other normal tissues. A Mirk promoter construct was activated when C2C12 myoblasts were switched from growth to differentiation medium and was also activated by the Rho family members RhoA, Cdc42, and to a lesser degree Rac1, but not by MyoD or Myf5. Mirk protein levels increased following transient expression of constitutively active Cdc42-QL, RhoA-QL, or Rac1-QL in C2C12 cells. High concentrations of serum mitogens down-regulated Mirk through activation of the Ras-MEK-Erk pathway. As a result, Mirk transcription was induced by the MEK1 inhibitor PD98059 and by the switch from growth to differentiation medium. Mirk was induced with similar kinetics to another Rho-induced differentiation gene, myogenin. Mirk protein levels increased 10-fold within 24-48 h after primary cultured muscle cells; C2C12 mouse myoblasts or L6 rat myoblasts were induced to differentiate. Thus Mirk was induced following the commitment stage of myogenesis. Stable overexpression of Mirk enabled myoblasts to fuse more rapidly when placed in differentiation medium. The function of Mirk in muscle differentiation was established by depletion of endogenous Mirk by small interfering RNA, which prevented myoblast fusion into myotubes and inhibited induction of markers of differentiation, including myogenin, fast twitch troponin T, and muscle myosin heavy chain. Other members of the dyrk/minibrain/HIPK family of kinases in lower organisms have been shown to regulate the transition from growth to differentiation, and Mirk is now shown to participate in skeletal muscle development.

Functional cooperation between multiple regulatory elements in the untranslated exon 1 stimulates the basal transcription of the human GnRH-II gene

The wide distribution of GnRH-II and conservation of its structure over all vertebrate classes suggest that the neuropeptide possesses vital biological functions. Although recent studies have shown that the expression of the human GnRH-II gene is regulated by cAMP and estrogen, the molecular mechanisms governing its basal transcription remain poorly understood. Using the neuronal TE-671 and placental JEG-3 cells, we showed that the minimal human GnRH-II promoter was located between nucleotide -1124 and -750 (relative to the translation start codon) and that the untranslated exon 1 was important to produce full promoter activity. Two putative E-box binding sites and one Ets-like element were identified within the first exon, and mutational analysis demonstrated that these cis-acting elements functioned cooperatively to stimulate the human GnRH-II gene transcription. EMSAs, UV cross-linking, and Southwestern blot analyses indicated that the basic helix-loop-helix transcription factor AP-4 bound specifically to the two E-box binding sites, whereas an unidentified protein bound to the Ets-like element. The functional importance of AP-4 in controlling human GnRH-II gene transcription was demonstrated by overexpression of sense and antisense full-length AP-4 cDNAs. Taken together, our present data demonstrate a novel mechanism in stimulating basal human GnRH-II gene transcription mediated by cooperative actions of multiple regulatory elements within the untranslated first exon of the gene.

Regulation of PRAK subcellular location by p38 MAP kinases

The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in cellular responses to inflammatory stimuli and environmental stress. p38 regulated/activated protein kinase (PRAK, also known as mitogen-activated protein kinase activated protein kinase 5 [MAPKAPK5]) functions downstream of p38alpha and p38beta in mediating the signaling of the p38 pathway. Immunostaining revealed that endogenous PRAK was predominantly localized in the cytoplasm. Interestingly, ectopically expressed PRAK was localized in the nucleus and can be redistributed by coexpression of p38alpha or p38beta to the locations of p38alpha and p38beta. Mutations in the docking groove on p38alpha/p38beta, or the p38-docking site in PRAK, disrupted the PRAK-p38 interaction and impaired the ability of p38alpha and p38beta to redistribute ectopically expressed PRAK, indicating that the location of PRAK could be controlled by its docking interaction with p38alpha and p38beta. Although the majority of PRAK molecules were detected in the cytoplasm, PRAK is consistently shuttling between the cytoplasm and the nucleus. A sequence analysis of PRAK shows that PRAK contains both a putative nuclear export sequence (NES) and a nuclear localization sequence (NLS). The shuttling of PRAK requires NES and NLS motifs in PRAK and can be regulated through cellular activation induced by stress stimuli. The nuclear content of PRAK was reduced after stimulation, which resulted from a decrease in the nuclear import of PRAK and an increase in the nuclear export of PRAK. The nuclear import of PRAK is independent from p38 activation, but the nuclear export requires p38-mediated phosphorylation of PRAK. Thus, the subcellular distribution of PRAK is determined by multiple factors including its own NES and NLS, docking interactions between PRAK and docking proteins, phosphorylation of PRAK, and cellular activation status. The p38 MAPKs not only regulate PRAK activity and PRAK activation-related translocation, but also dock PRAK to selected subcellular locations in resting cells.

Mkp1 and Mkp2, two MAPKAP-kinase homologues in Schizosaccharomyces pombe, interact with the MAP kinase Sty1

Mkp1 ( MAPKAP kinase Schizosaccharomyces pombe 1) and Mkp2 are two members from fission yeast of the sub-class of putative MAPK-activated protein kinases in yeasts, the other known members being Rck1 and Rck2 from Saccharomyces cerevisiae. The Mkp1 protein is readily co-immunoprecipitated with Sty1 from S. pombe extracts; Mkp2 shows a weaker interaction with Sty1. In mkp1 mutants, conjugation and meiosis proceed more readily and rapidly than in wild-type cells, in analogy to what was previously found for S. cerevisiae rck1 mutants. Conversely, overexpression of mkp1(+) delays meiosis. Mkp1 is phosphorylated in vivo in a sty1(+)-dependent manner; this modification is removed when cells are starved for nitrogen, a condition that is conducive to entry into stationary phase and meiosis. Overexpression of mkp1(+), like a sty1 mutation, also causes vegetative cells to elongate. The level of Mkp1 phosphorylation drops as cells enter mitosis. We have localised Mkp1 to the cytoplasm, excluded from the nucleus, in vegetative cells. The Mkp1 protein accumulates in zygotic asci and is concentrated within spores. The mkp2(+) gene has no noticeable impact on meiosis. Mkp2 is excluded from the nucleus in vegetative cells, and is concentrated at the septa of dividing cells. Mkp2 does not accumulate in meiotic cells.

Structure of mitogen-activated protein kinase-activated protein (MAPKAP) kinase 2 suggests a bifunctional switch that couples kinase activation with nuclear export

MAPK-activated protein kinase 2 (MAPKAPK2), one of several kinases directly phosphorylated and activated by p38 MAPK, plays a central role in the inflammatory response. The activated MAPKAPK2 phosphorylates its nuclear targets CREB/ATF1, serum response factor, and E2A protein E47 and its cytoplasmic targets HSP25/27, LSP-1, 5-lipoxygenase, glycogen synthase, and tyrosine hydroxylase. The crystal structure of unphosphorylated MAPKAPK2, determined at 2.8 A resolution, includes the kinase domain and the C-terminal regulatory domain. Although the protein is inactive, the kinase domain adopts an active conformation with aspartate 366 mimicking the missing phosphorylated threonine 222 in the activation loop. The C-terminal regulatory domain forms a helix-turn-helix plus a long strand. Phosphorylation of threonine 334, which is located between the kinase domain and the C-terminal regulatory domain, may serve as a switch for MAPKAPK2 nuclear import and export. Phosphorylated MAPKAPK2 masks the nuclear localization signal at its C terminus by binding to p38. It unmasks the nuclear export signal, which is part of the second C-terminal helix packed along the surface of kinase domain C-lobe, and thereby carries p38 to the cytoplasm.

Both binding and activation of p38 mitogen-activated protein kinase (MAPK) play essential roles in regulation of the nucleocytoplasmic distribution of MAPK-activated protein kinase 5 by cellular stress

The p38 mitogen-activated protein kinase (MAPK) pathway is an important mediator of cellular responses to environmental stress. Targets of p38 include transcription factors, components of the translational machinery, and downstream serine/threonine kinases, including MAPK-activated protein kinase 5 (MK5). Here we have used enhanced green fluorescent protein fusion proteins to analyze the subcellular localization of MK5. Although this protein is predominantly nuclear in unstimulated cells, MK5 shuttles between the nucleus and the cytoplasm. Furthermore, we have shown that the C-terminal domain of MK5 contains both a functional nuclear localization signal (NLS) and a leucine-rich nuclear export signal (NES), indicating that the subcellular distribution of this kinase reflects the relative activities of these two signals. In support of this, we have shown that stress-induced activation of the p38 MAPK stimulates the chromosomal region maintenance 1 protein-dependent nuclear export of MK5. This is regulated by both binding of p38 MAPK to MK5, which masks the functional NLS, and stress-induced phosphorylation of MK5 by p38 MAPK, which either activates or unmasks the NES. These properties may define the ability of MK5 to differentially phosphorylate both nuclear and cytoplasmic targets or alternatively reflect a mechanism whereby signals initiated by activation of MK5 in the nucleus may be transmitted to the cytoplasm.

In the cellular garden of forking paths: how p38 MAPKs signal for downstream assistance

Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved enzymes which connect cell-surface receptors to regulatory targets within cells and convert receptor signals into various outputs. In mammalian cells, four distinct MAPKs have been identified: the extracellular signal-related kinases (ERK)-1/2, the c-jun N-terminal kinases or stress-activated protein kinases 1 (JNK1/2/3, or SAPK1s), the p38 MAPKs (p38 alpha/beta/gamma/delta, or SAPK2s), and the ERK5 or big MAP kinase 1 (BMK1). The p38 MAPK cascade is activated by stress or cytokines and leads to phosphorylation of its central elements, the p38 MAPKs. Downstream of p38 MAPKs there is a diversification and extensive branching of signalling pathways. For that reason, we will focus in this review on the different signalling events that are triggered by p38 activity, and analyse how these events contribute to specific gene expression and cellular responses.

Human cell lines engineered for tetracycline-regulated expression of tumor suppressor candidate genes from a frequently affected chromosomal region, 3p21

BACKGROUND

We modified a tetracycline-regulated system that can control the activity of individual genes quantitatively and reversibly in transgenic mammals. Despite these advances, there remained one problem in the intensive use of the tet-system: the limited range of acceptor cell lines, expressing a tetracycline-controlled transcriptional activator (tTA). This study describes in detail new vectors and a unifying strategy to generate tTA-expressing cell lines.

METHOD

Two retroviral vectors pLNCtTA-hCMV and pLNCtTA-EF1alpha coding for the tTA were used to engineer cell lines to constitutively express tTA. New expression vectors pETE-Hyg and pETE-Bsd were also created that replicate in episomal form in human cells and facilitate tetracycline-regulated expression of targeted genes.

RESULTS

The primate-tropic retroviruses efficiently delivered the regulatory tTA gene into 12 selected human cancer cell lines. Two candidate tumor suppressor genes from the human 3p21-p22 region MAPKAPK3 (3pK) and MLH1 were cloned into the episomal vector and transfected into engineered A9 and KRC/Y cells. The transfectants were subcutaneously grown in SCID mice, and the expression of the transgene was successfully controlled in vivo by tetracycline administered ad libitum in drinking water. The experiments demonstrated that both transgenes did not antagonize the tumorous growth of these cells.

CONCLUSIONS

New retroviral and episomal vectors appear particularly suited for tight regulation of genes that cause suppression of cell growth. The generated cell lines can be used in various applications to study the effect of an inducible transgene in human cancer cells.

E protein function in lymphocyte development

Lymphocytes arise from hematopoietic stem cells through the coordinated action of transcription factors. The E proteins (E12, E47, HEB and E2-2) have emerged as key regulators of both B and T lymphocyte differentiation. This review summarizes the current data and examines the various functions of E proteins and their antagonists, Id2 and Id3, throughout lymphoid maturation. Beyond an established role in B and T lineage commitment, E proteins continue to be essential at subsequent stages of development. E protein activity regulates the expression of surrogate and antigen receptor genes, promotes Ig and TCR rearrangements, and coordinates cell survival and proliferation with developmental progression in response to TCR signaling. Finally, this review also discusses the role of E47 as a tumor suppressor.

Human serum and glucocorticoid-inducible kinase-like kinase (SGKL) phosphorylates glycogen syntheses kinase 3 beta (GSK-3beta) at serine-9 through direct interaction

Serum and glucocorticoid-inducible kinase-like kinase (SGKL) has been identified as a new integrator that decodes lipid signals produced by the activation of phosphoinositide 3-kinase (PI3K). SGKL is activated via its lipid-binding domain (phox homology domain) in response to PI3K signaling. However, downstream targets of SGKL as well as the role of SGKL as a mediator in PI3K signaling in human tissues remain to be established. In this study, we identified human glycogen synthase kinase 3 beta (GSK-3beta) as a specific interacting partner with SGKL in a yeast two-hybrid screening of human brain cDNA library. The association between these two proteins is confirmed independently in human embryonic kidney (HEK293) cells by co-immunoprecipitation. Furthermore, the kinase activity of wild-type SGKL was required for the in vitro phosphorylation of a GSK-3 crosstide fusion protein at serine-21/9 as demonstrated with a Phospho-GSK-3alpha/beta (Ser21/9) specific antibody. The present results provide strong evidences that SGKL could utilize GSK-3beta as a direct downstream target by phosphorylating GSK-3beta at serine-9.

Microarray analysis of B-cell stimulation

B-cell development to antibody-producing plasma cells requires the concerted function of a large number of genes and proteins. Genome-level expression profiling during human B-cell maturation was studied in anti-immunoglobulin M-stimulated Ramos cells. cDNA microarrays were used to follow changes in the transcriptome over several days. Close to 1500 genes had significantly altered expression at least at one time point. The genes were organized into clusters based on expression profiles and were further characterized based on the functions of the coded proteins. Several groups of genes important for B cells were analyzed. Here we concentrate on genes involved in signal transduction and cytokines and their receptors. The results provide knowledge on the development of humoral immunity. Several new genes were found to be essential for B-cell development. They can be used as targets for research and possibly for drug development.

Posttranslational mechanisms regulate the mammalian circadian clock

We have examined posttranslational regulation of clock proteins in mouse liver in vivo. The mouse PERIOD proteins (mPER1 and mPER2), CLOCK, and BMAL1 undergo robust circadian changes in phosphorylation. These proteins, the cryptochromes (mCRY1 and mCRY2), and casein kinase I epsilon (CKIepsilon) form multimeric complexes that are bound to DNA during negative transcriptional feedback. CLOCK:BMAL1 heterodimers remain bound to DNA over the circadian cycle. The temporal increase in mPER abundance controls the negative feedback interactions. Analysis of clock proteins in mCRY-deficient mice shows that the mCRYs are necessary for stabilizing phosphorylated mPER2 and for the nuclear accumulation of mPER1, mPER2, and CKIepsilon. We also provide in vivo evidence that casein kinase I delta is a second clock relevant kinase.

CR2/CD21 proximal promoter activity is critically dependent on a cell type-specific repressor

Transcription of the human complement receptor type 2 (CR2/CD21) gene is controlled by both proximal promoter and intronic elements. CR2 is primarily expressed on B cells from the immature through mature cell stages. We have previously described the presence of an intronic element that is required for both cell- and stage-specific expression of CR2. In this study, we report the identification of a cell type-specific repressor element within the proximal promoter. This repressor sequence is shown by linker scanning mutagenesis to comprise an E box motif. By supershift analysis this element binds members of the basic helix-loop-helix family of proteins, in particular E2A gene products. Mutational analysis demonstrates that binding of E2A proteins is critical for functioning of this repressor. Thus, E2A activity is key not only for early B cell development, but also for controlling CR2 expression, a gene expressed only during later stages of ontogeny.

The function of E- and Id proteins in lymphocyte development

Helix-loop-helix proteins are essential factors for lymphocyte development and function. In particular, E-proteins are crucial for commitment of lymphoid progenitors to the B- and T-cell lineages. E-proteins are negatively regulated by the Id class of helix-loop-helix proteins. The Id proteins function as dominant-negative inhibitors of E-proteins by inhibiting their ability to bind DNA. Here, we review the role of E-proteins and their Id protein antagonists in lymphocyte proliferation and developmental progression. In addition, we discuss how E-protein activity and Id gene expression are regulated by T-cell receptor (TCR) and pre-TCR-mediated signalling.