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Biomedical subjects

M Karin

Publications and source records attributed to M Karin.

At least 37 records · Page 2Linked to original sources
PubMed2001

HLA alleles and haplotypes in the Turkish population: relatedness to Kurds, Armenians and other Mediterraneans.

Turkish and Kurdish HLA profiles are studied for the first time. The comparative study of their allele frequencies, characteristic haplotypes, genetic distances with other Mediterraneans is complemented by neighbor-joining dendrograms and correspondence analyses. Turks, Kurds, Armenians, Iranians, Jews, Lebanese and other (Eastern and Western) Mediterranean groups seem to share a common ancestry: the older "Mediterranean" substratum. No sign of the postulated Indo-European (Aryan) invasion (1200 B.C.) is detected by our genetic analysis. It is concluded that this invasion, if occurred, had a relatively few invaders in comparison to the already settled populations, i.e. Anatolian Hittite and Hurrian groups (older than 2000 B.C.). These may have given rise to present-day Kurdish, Armenian and Turkish populations.

Alleles↗
PubMed2001

The alpha and beta subunits of IkappaB kinase (IKK) mediate TRAF2-dependent IKK recruitment to tumor necrosis factor (TNF) receptor 1 in response to TNF.

The activation of IkappaB kinase (IKK) is a key step in the nuclear translocation of the transcription factor NF-kappaB. IKK is a complex composed of three subunits: IKKalpha, IKKbeta, and IKKgamma (also called NEMO). In response to the proinflammatory cytokine tumor necrosis factor (TNF), IKK is activated after being recruited to the TNF receptor 1 (TNF-R1) complex via TNF receptor-associated factor 2 (TRAF2). We found that the IKKalpha and IKKbeta catalytic subunits are required for IKK-TRAF2 interaction. This interaction occurs through the leucine zipper motif common to IKKalpha, IKKbeta, and the RING finger domain of TRAF2, and either IKKalpha or IKKbeta alone is sufficient for the recruitment of IKK to TNF-R1. Importantly, IKKgamma is not essential for TNF-induced IKK recruitment to TNF-R1, as this occurs efficiently in IKKgamma-deficient cells. Using TRAF2(-/-) cells, we demonstrated that the TNF-induced interaction between IKKgamma and the death domain kinase RIP is TRAF2 dependent and that one possible function of this interaction is to stabilize the IKK complex when it interacts with TRAF2.

Animals↗
PubMed2001

AP-1 repressor protein JDP-2: inhibition of UV-mediated apoptosis through p53 down-regulation.

Members of the AP-1 transcription factor family, especially c-Jun and c-Fos, have long been known to mediate critical steps in the cellular response to ultraviolet (UV) irradiation. We sought to examine whether two newly discovered members of the AP-1 family, JDP-1 and JDP-2, also participate in the mammalian UV response. Here we report that JDP-2, but not JDP-1, is transiently induced upon UV challenge and that elevated levels of JDP-2 increase cell survival following UV exposure. This protective function of JDP-2 appears to be mediated through repression of p53 expression at the transcriptional level, via a conserved atypical AP-1 site in the p53 promoter.

3T3 Cells↗
PubMed2001

Prevention of fat-induced insulin resistance by salicylate.

Insulin resistance is a major factor in the pathogenesis of type 2 diabetes and may involve fat-induced activation of a serine kinase cascade involving IKK-beta. To test this hypothesis, we first examined insulin action and signaling in awake rats during hyperinsulinemic-euglycemic clamps after a lipid infusion with or without pretreatment with salicylate, a known inhibitor of IKK-beta. Whole-body glucose uptake and metabolism were estimated using [3-(3)H]glucose infusion, and glucose uptake in individual tissues was estimated using [1-(14)C]2-deoxyglucose injection during the clamp. Here we show that lipid infusion decreased insulin-stimulated glucose uptake and activation of IRS-1-associated PI 3-kinase in skeletal muscle but that salicylate pretreatment prevented these lipid-induced effects. To examine the mechanism of salicylate action, we studied the effects of lipid infusion on insulin action and signaling during the clamp in awake mice lacking IKK-beta. Unlike the response in wild-type mice, IKK-beta knockout mice did not exhibit altered skeletal muscle insulin signaling and action following lipid infusion. In summary, high-dose salicylate and inactivation of IKK-beta prevent fat-induced insulin resistance in skeletal muscle by blocking fat-induced defects in insulin signaling and action and represent a potentially novel class of therapeutic agents for type 2 diabetes.

Animals↗
PubMed2001

c-Jun N-terminal kinase is required for metalloproteinase expression and joint destruction in inflammatory arthritis.

Mitogen-activated protein kinase (MAPK) cascades are involved in inflammation and tissue destruction in rheumatoid arthritis (RA). In particular, c-Jun N-terminal kinase (JNK) is highly activated in RA fibroblast-like synoviocytes and synovium. However, defining the precise function of this kinase has been difficult because a selective JNK inhibitor has not been available. We now report the use of a novel selective JNK inhibitor and JNK knockout mice to determine the function of JNK in synoviocyte biology and inflammatory arthritis. The novel JNK inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one) completely blocked IL-1--induced accumulation of phospho-Jun and induction of c-Jun transcription in synoviocytes. Furthermore, AP-1 binding and collagenase mRNA accumulation were completely suppressed by SP600125. In contrast, complete inhibition of p38 had no effect, and ERK inhibition had only a modest effect. The essential role of JNK was confirmed in cultured synoviocytes from JNK1 knockout mice and JNK2 knockout mice, each of which had a partial defect in IL-1--induced AP-1 activation and collagenase-3 expression. Administration of SP600125 modestly decreased the rat paw swelling in rat adjuvant-induced arthritis. More striking was the near-complete inhibition of radiographic damage that was associated with decreased AP-1 activity and collagenase-3 gene expression. Therefore, JNK is a critical MAPK pathway for IL-1--induced collagenase gene expression in synoviocytes and in joint arthritis, indicating that JNK is an important therapeutic target for RA.

Activating Transcription Factor 2↗
PubMed2001

Potentiation of estrogen receptor activation function 1 (AF-1) by Src/JNK through a serine 118-independent pathway.

Estrogen receptor (ER) is activated either by ligand or by signals from tyrosine kinase-linked cell surface receptors. We investigated whether the nonreceptor Src tyrosine kinase could affect ER activity. Expression of constitutively active Src or stimulation of the endogenous Src/JNK pathway enhances transcriptional activation by the estrogen-ER complex and strongly stimulates the otherwise weak activation by the unliganded ER and the tamoxifen-ER complex. Src affects ER activation function 1 (AF-1), and not ER AF-2, and does so through its tyrosine kinase activity. This effect of Src is mediated partly through a Raf/mitogen-activated ERK kinase/extracellular signal-regulated kinase (Raf/MEK/ERK) signaling cascade and partly through a MEKK/JNKK/JNK cascade. Although, as previously shown, Src action through activated ERK stimulates AF-1 by phosphorylation at S118, Src action through activated JNK neither leads to phosphorylation of S118 nor requires S118 for its action. We therefore suggest that the Src/JNK pathway enhances AF-1 activity by modification of ER AF-1-associated proteins. Src potentiates activation functions in CREB-binding protein (CBP) and glucocorticoid receptor interacting protein 1 (GRIP1), and we discuss the possibility that the Src/JNK pathway enhances the activity of these coactivators, which are known to mediate AF-1 action.

CREB-Binding Protein↗
PubMed2001

AP-1--glucocorticoid receptor crosstalk taken to a higher level.

More than a decade ago our view of gene regulation by glucocorticoids (GC) and other steroid hormones underwent a dramatic change with the discovery of negative crosstalk (transcriptional interference) between the GC receptor (GCR) and transcription factor AP-1 (Jun:Fos). It was initially observed that induction of the collagenase type 1 gene, which is mediated through activation of AP-1 by growth factors and inflammatory cytokines, is repressed by GC. This repression was attributed to mutual negative interactions between AP-1 and GCR. Although the exact molecular mechanism underlying this particular case of transcriptional interference is yet to be determined, it has become clear that this and analogous interactions with other transcription factors (e.g. nuclear factor-kappaB) underlie the anti-inflammatory and immunosuppressive activity of GC. Recent studies conducted at the whole animal level indicate that the interactions between the AP-1 and GC signaling pathways are much more extensive. AP-1-related signaling via the Jun N-terminal kinases can lead to increased levels of circulating GC, which eventually down-modulate AP-1 activity via transcriptional interference. This negative feedback loop is likely to be of great importance for maintenance of homeostasis and regulation of stress responses, including acute and chronic inflammation.

Gene Expression Regulation↗
PubMed2000

ATM is required for IkappaB kinase (IKKk) activation in response to DNA double strand breaks.

Following challenge with proinflammatory stimuli or generation of DNA double strand breaks (DSBs), transcription factor NF-kappaB translocates from the cytoplasm to the nucleus to activate expression of target genes. In addition, NF-kappaB plays a key role in protecting cells from proapoptotic stimuli, including DSBs. Patients suffering from the genetic disorder ataxia-telangiectasia, caused by mutations in the ATM gene, are highly sensitive to inducers of DSBs, such as ionizing radiation. Similar hypersensitivity is displayed by cell lines derived from ataxia-telangiectasia patients or Atm knockout mice. The ATM protein, a member of the phosphatidylinositol 3-kinase (PI3K)-like family, is a multifunctional protein kinase whose activity is stimulated by DSBs. As both ATM and NF-kappaB deficiencies result in increased sensitivity to DSBs, we examined the role of ATM in NF-kappaB activation. We report that ATM is essential for NF-kappaB activation in response to DSBs but not proinflammatory stimuli, and this activity is mediated via the IkappaB kinase complex. DNA-dependent protein kinase, another member of the PI3K-like family, PI3K itself, and c-Abl, a nuclear tyrosine kinase, are not required for this response.

Androstadienes↗
PubMed2000

The mammalian UV response: c-Jun induction is required for exit from p53-imposed growth arrest.

The mammalian UV response results in rapid and dramatic induction of c-jun. Induction of a protooncogene, normally involved in mitogenic responses, by a genotoxic agent that causes growth arrest seems paradoxical. We now provide an explanation for the role of c-Jun in the UV response of mouse fibroblasts. c-Jun is necessary for cell-cycle reentry of UV-irradiated cells, but does not participate in the response to ionizing radiation. Cells lacking c-Jun undergo prolonged cell-cycle arrest, but resist apoptosis, whereas cells that express c-Jun constitutively do not arrest and undergo apoptosis. This function of c-Jun is exerted through negative regulation of p53 association with the p21 promoter. Cells lacking c-Jun exhibit prolonged p21 induction, whereas constitutive c-Jun inhibits UV-mediated p21 induction.

Animals↗
PubMed2000

DNA-PKcs is required for activation of innate immunity by immunostimulatory DNA.

Bacterial DNA and related synthetic immunostimulatory oligodeoxyribonucleotides (ISS-ODN) stimulate innate immunity. However, the molecular recognition mechanism that initiates signaling in response to bacterial DNA and ISS-ODN has not been identified. Herein, we demonstrate that administration of bacterial DNA and ISS-ODN to mice lacking the catalytic subunit of DNA-PK (DNA-PKcs) and in vitro stimulation of BMDM from these mice result in defective induction of IL-6 and IL-12. Further analysis using BMDM of IKKbeta(-/-) revealed that both DNA-PKcs and IKKbeta are essential for normal cytokine production in response to ISS-ODN or bacterial DNA. ISS-ODN and bacterial DNA activate DNA-PK, which in turn contributes to activation of IKK and NF-kappaB. These results reveal a novel role of DNA-PKcs in innate immune responses and a link between DNA repair and innate immunity.

Androstadienes↗
PubMed2000

Inhibition of NF-kappa B activation by arsenite through reaction with a critical cysteine in the activation loop of Ikappa B kinase.

Arsenite is a potent environmental toxin that causes various pathologies including cancers and skin disorders. Arsenite is believed to exert its biological effects through reaction with exposed sulfhydryl groups, especially pairs of adjacent thiols. Here, we describe the mechanism by which arsenite affects the NF-kappaB signaling pathway. Activation of transcription factor NF-kappaB depends on the integrity of the IkappaB kinase (IKK) complex. We found that arsenite potently inhibits NF-kappaB and IKK activation by binding to Cys-179 in the activation loop of the IKK catalytic subunits, IKKalpha/beta. The affinity of IKKbeta for trivalent arsenic was verified in vitro by the ability of IKKbeta to enhance the fluorescence of an arsenic-substituted fluorescein dye. The addition of 1,2-dithiol antidotes or replacement of Cys-179 with an alanine residue abolished dye binding to and arsenite inhibition of IKKbeta. Overexpression of IKKbeta (C179A) protects NF-kappaB from inhibition by arsenite, indicating that despite the involvement of a large number of distinct gene products in this activation pathway, the critical target for inhibition by arsenite is on the IKK catalytic subunits.

Amino Acid Sequence↗
PubMed2000

Requirement for p38alpha in erythropoietin expression: a role for stress kinases in erythropoiesis.

Activity of the p38alpha MAP kinase is stimulated by various stresses and hematopoietic growth factors. A role for p38alpha in mouse development and physiology was investigated by targeted disruption of the p38alpha locus. Whereas some p38alpha(-/-) embryos die between embryonic days 11.5 and 12.5, those that develop past this stage have normal morphology but are anemic owing to failed definitive erythropoiesis, caused by diminished erythropoietin (Epo) gene expression. As p38alpha-deficient hematopoietic stem cells reconstitute lethally irradiated hosts, p38alpha function is not required downstream of Epo receptor. Inhibition of p38 activity also interferes with stabilization of Epo mRNA in human hepatoma cells undergoing hypoxic stress. The p38alpha MAP kinase plays a critical role linking developmental and stress-induced erythropoiesis through regulation of Epo expression.

Anemia↗
PubMed2000

Differentiation of lactotrope precursor GHFT cells in response to fibroblast growth factor-2.

The mechanisms that control the emergence of different anterior pituitary cells from a common stem cell population are largely unknown. The immortalized GHFT cells derived from targeted expression of SV40 T antigen to mouse pituitary display characteristics of somatolactotropic progenitors in that they express the transcription factor GHF-1 (Pit-1) but not growth hormone (GH) or prolactin (PRL). We searched for factors capable of inducing lactotropic differentiation of GHFT cells. PRL gene expression was not observed in cells subjected to a variety of stimuli, which induce PRL gene expression in mature lactotropes. Only fibroblast growth factor-2 (FGF-2) was able to initiate the transcription, synthesis, and release of PRL in GHFT cells. However, induction of PRL expression was incomplete in FGF-2-treated cells, suggesting that additional factors are necessary to attain high levels of PRL transcription in fully differentiated lactotropes. We also show that the FGF-2 response element is located in the proximal PRL promoter. Stimulation of PRL expression by FGF-2 requires endogenous Ets factors and these factors as well as GHF-1 are expressed at low levels in the committed precursor, suggesting that these low levels are limiting for full PRL expression. Moreover, FGF-2 effect on lactotrope differentiation is mediated, at least partially, by stimulation of the Ras-signaling pathway. Our results suggest that, indeed, GHFT cells represent a valid model for studying lactotropic differentiation and that FGF-2 could play a key role both in initiating lactotrope differentiation and maintaining PRL expression.

Animals↗
PubMed2000

Cell cycle-regulated modification of the ribosome by a variant multiubiquitin chain.

Ubiquitin is ligated to L28, a component of the large ribosomal subunit, to form the most abundant ubiquitin-protein conjugate in S. cerevisiae. The human ortholog of L28 is also ubiquitinated, indicating that this modification is highly conserved in evolution. During S phase of the yeast cell cycle, L28 is strongly ubiquitinated, while reduced levels of L28 ubiquitination are observed in G1 cells. L28 ubiquitination is inhibited by a Lys63 to Arg substitution in ubiquitin, indicating that L28 is modified by a variant, Lys63-linked multiubiquitin chain. The K63R mutant of ubiquitin displays defects in ribosomal function in vivo and in vitro, including a dramatic sensitivity to translational inhibitors. L28, like other ribosomal proteins, is metabolically stable. Therefore, these data suggest a regulatory role for multiubiquitin chains that is reversible and does not function to target the acceptor protein for degradation.

Amino Acid Sequence↗
PubMed2000

Nucleolin and YB-1 are required for JNK-mediated interleukin-2 mRNA stabilization during T-cell activation.

Regulated mRNA turnover is a highly important process, but its mechanism is poorly understood. Using interleukin-2 (IL-2) mRNA as a model, we described a role for the JNK-signaling pathway in stabilization of IL-2 mRNA during T-cell activation, acting via a JNK response element (JRE) in the 5' untranslated region (UTR). We have now identified two major RNA-binding proteins, nucleolin and YB-1, that specifically bind to the JRE. Binding of both proteins is required for IL-2 mRNA stabilization induced by T-cell activation signals and for JNK-induced stabilization in a cell-free system that duplicates essential features of regulated mRNA decay. Nucleolin and YB-1 are required for formation of an IL-2 mRNP complex that responds to specific mRNA stabilizing signals.

Amino Acid Sequence↗
PubMed2000

MEK kinase 1 is critically required for c-Jun N-terminal kinase activation by proinflammatory stimuli and growth factor-induced cell migration.

Exposure of eukaryotic cells to extracellular stimuli results in activation of mitogen-activated protein kinase (MAPK) cascades composed of MAPKs, MAPK kinases (MAP2Ks), and MAPK kinase kinases (MAP3Ks). Mammals possess a large number of MAP3Ks, many of which can activate the c-Jun N-terminal kinase (JNK) MAPK cascade when overexpressed, but whose biological function is poorly understood. We examined the function of the MAP3K MEK kinase 1 (MEKK1) in proinflammatory signaling. Using MEKK1-deficient embryonic stem cells prepared by gene targeting, we find that, in addition to its function in JNK activation by growth factors, MEKK1 is required for JNK activation by diverse proinflammatory stimuli, including tumor necrosis factor alpha, IL-1, double-stranded RNA, and lipopolysaccharide. MEKK1 is also essential for induction of embryonic stem cell migration by serum factors, but is not required for activation of other MAPKs or the IkappaB kinase signaling cascade.

Animals↗