Characterization of the structure and function of a new mitogen-activated protein kinase (p38beta)

Combined action of extracellular signal-regulated kinase and p38 kinase rescues Molt4 T cells from nitric oxide-induced apoptotic and necrotic cell death

The mechanisms that regulate nitric oxide (NO)-induced apoptosis, especially in T cell apoptosis, are largely uncharacterized. Here, we report that protection from NO-induced cell death by phorbol 12-myristate 13-acetate (PMA) is dependent on both p38 and extracellular signal-regulated kinase (ERK) activation. Exposure of Molt4 cells to NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) induced both apoptotic and necrotic modes of cell death along with a sustained increase in p38 kinase phosphorylation. However, the p38 inhibitor SB202190 only slightly protected Molt4 cells from NO toxicity. In contrast, PMA rapidly phosphorylated both p38 kinase and ERK, and the phosphorylation statuses were not altered in the presence of SNAP. Interestingly, although each mitogen-activated protein kinase (MAPK) inhibitor by itself had only a modest effect, the combination of inhibitors for both MAPKs almost completely abolished the protective effect of PMA. Furthermore, dominant negative or catalytically inactive variants that modulate p38 and ERK mimicked the effects of MAPK inhibitors. We located the action of p38 and ERK upstream of the p53/mitochondrial membrane potential loss and caspases cascade. Together, these findings suggest that the PMA-induced activations of ERK and p38 kinase are parallel events that are both required for inhibition of NO-induced death of Molt4 cells.

Essential role of p38 mitogen-activated protein kinase in cathepsin K gene expression during osteoclastogenesis through association of NFATc1 and PU.1

The receptor activator of NF-kappaB ligand (RANKL) induces various osteoclast-specific marker genes during osteoclast differentiation mediated by mitogen-activated protein (MAP) kinase cascades. However, the results of transcriptional programming of an osteoclast-specific cathepsin K gene are inconclusive. Here we report the regulatory mechanisms of RANKL-induced cathepsin K gene expression during osteoclastogenesis in a p38 MAP kinase-dependent manner. The reporter gene analysis with sequential 5'-deletion constructs of the cathepsin K gene promoter indicates that limited sets of the transcription factors such as NFATc1, PU.1, and microphthalmia transcription factor indeed enhance synergistically the gene expression when overexpressed in RAW264 cells. In addition, the activation of p38 MAP kinase is required for the maximum enhancement of the gene expression. RANKL-induced NFATc1 forms a complex with PU.1 in nuclei of osteoclasts following the nuclear accumulation of NFATc1 phosphorylated by the activated p38 MAP kinase. These results suggest that the RANKL-induced cathepsin K gene expression is cooperatively regulated by the combination of the transcription factors and p38 MAP kinase in a gradual manner.

The orphan nuclear receptor SHP is involved in monocytic differentiation, and its expression is increased by c-Jun

Small heterodimer partner (SHP) is an atypical member of nuclear receptor superfamily that lacks a DNA binding domain. Here, we show that SHP expression increases during monocytic differentiaton with exposure HL-60 leukemia cells to a 12-O-tetradecanoylphorbol-13-acetate (TPA) response element, whose treatment induced the SHP promoter activity dependent on c-Jun expression, which is well known to be involved in the commitment step in the TPA-induced differentiation of HL-60 leukemia cells. We also show that overexpression and activation signaling of c-Jun increase the SHP promoter activity, suggesting that the level of SHP expression is normally limiting for c-Jun-dependent monocytic differentiation. Electrophoretic mobility shift assays using oligonucleotides derived from the SHP promoter reveal that c-Jun exhibit TPA-induced DNA binding, providing a mechanism for the transcriptional activation of SHP gene expression. It was also found that overexpression of SHP and c-Jun greatly facilitated monocytic differentiation by TPA and surprisingly, that expression of SHP or c-Jun alone was sufficient to make cells differentiate into functionally mature monocytes, but silencing of SHP and c-Jun by RNA interference diminished the TPA-induced monocytic differentiation. Taken together, these works suggest that c-Jun works to activate the expression of SHP genes associated with the cascade regulation of monocytic differentiation.

Active mutants of the human p38alpha mitogen-activated protein kinase

Mitogen-activated protein (MAP) kinases compose a family of serine/threonine kinases that function in many signal transduction pathways and affect various cellular phenotypes. Despite the abundance of available data, the exact role of each MAP kinase is not completely defined, in part because of the inability to activate MAP kinase molecules individually and specifically. Based on activating mutations found in the yeast MAP kinase p38/Hog1 (Bell, M., Capone, R., Pashtan, I., Levitzki, A., and Engelberg, D. (2001) J. Biol. Chem. 276, 25351-25358), we designed and constructed single and multiple mutants of human MAP kinase p38alpha. Single (p38D176A, p38F327L, and p38F327S) and subsequent double (p38D176A/F327L and p38D176A/F327S) mutants acquired high intrinsic activity independent of any upstream regulation and reached levels of 10 and 25%, respectively, in reference to the dually phosphorylated wild type p38alpha. The active p38 mutants have retained high specificity toward p38 substrates and were inhibited by the specific p38 inhibitors SB-203580 and PD-169316. We also show that similar mutations can render p38gamma active as well. Based on the available structures of p38 and ERK2, we have analyzed the p38 mutants and identified a hydrophobic core stabilized by three aromatic residues, Tyr-69, Phe-327, and Trp-337, in the vicinity of the L16 loop region. Upon activation, a segment of the L16 loop, including Phe-327, becomes disordered. Structural analysis suggests that the active p38 mutants emulate the conformational changes imposed naturally by dual phosphorylation, namely, destabilization of the hydrophobic core. Essentially, the hydrophobic core is an inherent stabilizer that maintains low basal activity level in unphosphorylated p38.

Regulation of Involucrin Gene Expression

The epidermis is a dynamic renewing structure that provides life-sustaining protection from the environment. The major cell type of the epidermis, the epidermal keratinocyte, undergoes a carefully choreographed program of differentiation. Alteration of these events results in a variety of debilitating and life-threatening diseases. Understanding how this process is regulated is an important current goal in biology. In this review, we summarize the literature regarding regulation of involucrin, an important marker gene that serves as a model for understanding the mechanisms that regulate the differentiation process. Current knowledge describing the role of transcription factors and signaling cascades in regulating involucrin gene expression are presented. These studies describe a signaling cascade that includes the novel protein kinase C isoforms, Ras, MEKK1, MEK3, and a p38delta-extracellular signal regulated kinase 1/2 complex. This cascade regulates activator protein one, Sp1, and CCATT/enhancer-binding protein transcription factor DNA binding to two discrete involucrin promoter regions, the distal- and proximal-regulatory regions, to regulate involucrin gene expression.

Activation of p38 MAPK during porcine oocyte maturation

The p38 MAPK is a member of the mitogen-activated protein kinase (MAPK) family that participates in a signaling cascade in response to cytokines and stress in somatic cells. The present study was designed to investigate the expression and possible function of p38 MAPK in porcine oocytes during maturation. In immunoblots, p38 MAPK was detected in oocytes and cumulus cells. Its activity was determined during oocyte maturation in vitro by the phosphorylation of its substrate, activated transcription factor 2. As ERK1/2, oocyte p38 MAPK became active around germinal vesicle breakdown (GVBD) and maintained activity until metaphase II (MII). Immunofluorescent microscopy showed phosphorylated p38 MAPK accumulated in the nucleus before GVBD and localized in the cytoplasm and around chromosomes from metaphase I (MI) to MII. In cultured cumulus-oocyte complexes, a specific inhibitor of p38 MAPK, SB203580, inhibited phosphorylation of p38 MAPK in cumulus cells and blocked both FSH-induced cumulus expansion and meiotic resumption of oocytes. During spontaneous meiotic resumption of denuded oocytes, SB203580 did not affect GVBD, but it significantly decreased the number of oocytes reaching MII and conversely increased the number of oocytes arrested at MI. These results suggest that p38 MAPK in porcine oocytes becomes active around GVBD, remains active through MI to MII, and has a role in MI-MII transition, and that cumulus p38 MAPK might be involved in FSH-induced meiotic resumption of oocytes.

Defective transcription factor activation for proinflammatory gene expression in poly(ADP-ribose) polymerase 1-deficient glia

Poly(ADP-ribose) polymerase 1 (PARP-1) activity is detected in both neuronal and nonneuronal cells in the CNS, and excessive PARP-1 activity is known to be detrimental to tissue because of the cellular energy loss. Accordingly, PARP-1-deficient (PARP-1(-/-)) mice have been shown to be resistant to cerebral ischemia and several forms of inflammation. Recently, PARP-1 in glial cells has been shown to mediate the expression of proinflammatory genes in response to inflammatory stimuli by, in part, enhancing cognate DNA-binding capacities of transcription factors such as NF-kappaB and activator protein 1. Here, we demonstrate an additional mechanism whereby a significant reduction of proinflammatory gene expression such as IL-1beta, tumor necrosis factor alpha, and inducible nitricoxide synthase in PARP-1(-/-) glial cells is linked to defective inflammatory stimuli-induced p38MAPK-mediated phosphorylation of ATF-2 and cAMP-response element-binding protein and phosphorylation of NF-kappaB p65. Importantly, an inflammatory stimuli-induced p38MAPK activation is impaired in PARP-1(-/-) glial cells in a signaling pathway- and cell/tissue type-specific manner. These findings indicate that PARP-1 is an essential host factor among factors that actively mediate excessive production of proinflammatory molecules in glial cells, which may in turn contribute to the initiation of neuronal injuries.

Regulation of Nrf2 transactivation domain activity. The differential effects of mitogen-activated protein kinase cascades and synergistic stimulatory effect of Raf and CREB-binding protein

Transcription factor NF-E2-related factor 2 (Nrf2) regulates the induction of Phase II detoxifying enzymes as well as anti-oxidative enzymes. In this study, we investigated the transactivation potential of different Nrf2 transactivation domain regions by using the Gal4-Nrf2 chimeras and Gal4-Luc reporter co-transfection assay system in HepG2 cells. The results indicated that chimera Gal4-Nrf2-(1-370), which contains the full transactivation domain showed very potent transactivation activity. The high transactivation activity of Gal4-Nrf2-(113-251) and the diminished transactivation activities of chimera Gal4-Nrf2-(1-126) and Gal4-Nrf2-(230-370) suggested that the Nrf2 N-terminal 113-251 amino acids region is critical in maintaining its transactivation activity. Overexpression of upstream MAPKs such as Raf, MEKK1, TAK1-DeltaN, and ASK1 up-regulated the transactivation activities of Gal4-Nrf2-(1-370) and Gal4-Nrf2-(113-251) in a dose-dependent manner. Further investigation on the effects of the three MAPK pathways on Nrf2 transactivation domain activity demonstrated that both ERK and JNK signaling pathways stimulated the Gal4-Nrf2-(1-370) transactivation activity while the p38 pathway played a negative role. Site-directed mutagenesis studies on potential MAPK phosphorylation sites of Gal4-Nrf2-(113-251) showed no significant effect on its basal transactivation activity or the fold of induction by Raf. Interestingly, the nuclear transcription coactivator CREB-binding protein (CBP), which can bind to Nrf2 transactivation domain and can be activated by ERK cascade, showed synergistic stimulation with Raf on the transactivation activities of both the chimera Gal4-Nrf2-(1-370) and the full-length Nrf2. Taken together, this study clearly demonstrated that different segments of Nrf2 transactivation domain have different transactivation potential and different MAPKs have differential effects on Nrf2 transcriptional activity. It also suggested that the up-regulation of Nrf2 transactivation domain activity by upstream MAPKs such as Raf may not be mediated by direct phosphorylation of the Nrf2 transactivation domain, but rather by regulation of the transcriptional activity of coactivator CBP.

Inhibition of p38 mitogen-activated protein kinase enhances adrenergic-stimulated arylalkylamine N-acetyltransferase activity in rat pinealocytes

We have previously shown that inhibition of p38(MAPK) increases adrenergic-stimulated p42/44(MAPK) activation in rat pinealocytes. In this study we investigated whether p38(MAPK) played a role in the adrenergic regulation of arylalkylamine-N-acetyltransferase (AA-NAT) induction and melatonin (MT) synthesis. Treatment of pinealocytes with norepinephrine (NE) caused a time-dependent increase in the levels of AA-NAT mRNA, AA-NAT protein, and enzymatic activity as well as MT production. Cotreatment with SB202190, a selective p38(MAPK) inhibitor, although having no effect on AA-NAT activity or protein level 3 h after NE treatment, caused a sustained increase in AA-NAT activity and protein level after 6 h of NE treatment. The increases in NE-stimulated AA-NAT activity and protein level by SB202190 occurred in the absence of an increase in AA-NAT mRNA. Similar results were obtained when AA-NAT was induced by (Bu)(2)cAMP or when SB203580 was used to inhibit p38(MAPK). In comparison, SB202474, the inactive analog, had no effect on NE or (Bu)(2)cAMP-stimulated AA-NAT activity or protein level. SB202190 also increased cumulative NE-stimulated MT production, provided that the medium was supplemented with 5-methoxytryptamine. p38(MAPK) inhibitors had no effect on hydroxyindole-O-methyltransferase activity. These results show that inhibition of p38(MAPK), although having no effect on cAMP-mediated AA-NAT transcription, appears to increase AA-NAT activity either by increasing translation or by reducing degradation of the AA-NAT protein. The lack of effect on NE-stimulated MT accumulation by p38(MAPK) inhibitors in the absence of 5-methoxytryptamine could be secondary to a lack of substrate, or alternatively, hydroxyindole-O-methyltransferase may become limiting.

Hypertonicity promotes survival of corticospinal motoneurons via mitogen-activated protein kinase p38 signaling

Extracellular hypertonicity can induce the phosphorylation of mitogen-activated protein kinases (MAPKs). Of these, both extracellular signal-regulated kinases (ERKs) and the stress-activated kinase p38 have been implicated in neuronal cell survival. Resuscitation with hypertonic saline decreases secondary brain injury after trauma, as well as neuronal damage, after ischemia. Since hypertonicity has been shown to support somatic cell survival, we investigated if hypertonicity can also prevent neuronal cell death via MAPK signaling. Death of postnatal rat corticospinal motoneurons (CSMNs) was induced by serum deprivation, and survival in both isotonic and hypertonic media was assessed after 20 h. Addition of NaCl (4-250 mM) to isotonic medium significantly and dose dependently protected CSMN in enriched cultures, increasing cell survival by up to 70% over that in isotonic medium. This response was not restricted to NaCl; addition of KCl, choline chloride, and sucrose had similar effects on cell survival. In addition, hypertonicity supported the survival of pure CSMN populations, albeit with lower potency. In cortical cell suspensions, hypertonic NaCl (20-100 mM) increased basal phosphorylation of p38 and ERK. The activation of both MAPKs, which was induced by 40 mM NaCl, was transient. Cultivation of CSMNs in media containing the specific p38 inhibitor SB203580 abolished the protective effect of hypertonic NaCl, indicating a central role for p38. We therefore conclude that hypertonicity can prevent neuronal cell death via MAPK signaling.

Chromatin-mediated regulation of nucleolar structure and RNA Pol I localization by TOR

The target of rapamycin (TOR) protein is a conserved regulator of ribosome biogenesis, an important process for cell growth and proliferation. However, how TOR is involved remains poorly understood. In this study, we find that rapamycin and nutrient starvation, conditions inhibiting TOR, lead to significant nucleolar size reduction in both yeast and mammalian cells. In yeast, this morphological change is accompanied by release of RNA polymerase I (Pol I) from the nucleolus and inhibition of ribosomal DNA (rDNA) transcription. We also present evidence that TOR regulates association of Rpd3-Sin3 histone deacetylase (HDAC) with rDNA chromatin, leading to site-specific deacetylation of histone H4. Moreover, histone H4 hypoacetylation mutations cause nucleolar size reduction and Pol I delocalization, while rpd3Delta and histone H4 hyperacetylation mutations block the nucleolar changes as a result of TOR inhibition. Taken together, our results suggest a chromatin-mediated mechanism by which TOR modulates nucleolar structure, RNA Pol I localization and rRNA gene expression in response to nutrient availability.

Inhibitors of p38 mitogen-activated protein kinase: potential as anti-inflammatory agents in asthma?

Asthma is an inflammatory disease of the airways, which in patients with mild to moderate symptoms is adequately controlled by either beta(2)-adrenoceptor agonists or corticosteroids, or a combination of both. Despite this, there are classes of patients that fail to respond to these treatments. In addition, there is a general trend towards increasing morbidity and mortality due to asthma, which suggests that there is a need for new and improved treatments. The p38 mitogen-activated protein kinases (MAPKs) represent a point of convergence for multiple signalling processes that are activated in inflammation and that impact on a diverse range of events that are important in inflammation. Small molecule pyridinyl imidazole inhibitors of p38 MAPK have proved to be highly effective in reducing various parameters of inflammation, in particular cytokine expression. Like corticosteroids, inhibitors of p38 MAPK appear to be able to repress gene expression at multiple levels, for example, by transcriptional, posttranscriptional and translational repression, and this raises the possibility of a similarly broad spectrum of anti-inflammatory activities. Indeed these molecules have proved to be effective in numerous in vitro and in vivo models of inflammation and septicaemia, which suggests that such compounds may be effective as therapeutic agents against inflammatory disorders. Despite these very promising indications of the possible therapeutic use of p38 MAPK inhibitors, a number of events that are p38-dependent are in fact also beneficial to the resolution or modulation of diseases such as asthma. We conclude that the overall effect of p38 MAPK inhibition would be beneficial in inflammatory diseases such as rheumatoid arthritis and asthma. However, these drugs may result in a complex phenotype that will require careful evaluation. Currently, a number of second or third generation inhibitors of p38 MAPK are being tested in phase I and phase II clinical trials.

Differentiation stage-specific activation of p38 mitogen-activated protein kinase isoforms in primary human erythroid cells

p38alpha, p38beta, p38gamma, and p38delta are four isoforms of p38 mitogen-activated protein (MAP) kinase (MAPK) involved in multiple cellular functions such as cell proliferation, differentiation, apoptosis, and inflammation response. In the present study, we examined the mRNA expression pattern of each of the four isoforms during erythroid differentiation of primary erythroid progenitors. We show that p38alpha and p38gamma transcripts are expressed in early hematopoietic progenitors as well as in late differentiating erythroblasts, whereas p38delta mRNA is only expressed and active during the terminal phase of erythroid differentiation. On the other hand, p38beta is minimally expressed in early CD34(+) hematopoietic progenitors but not expressed in lineage-committed erythroid progenitors. We also determined the phosphorylation/activation of p38alpha, MAPK kinase 3/6, and MAPKAP-2 in response to erythropoietin and stem cell factor. We found that phosphorylation of p38alpha, MAPK kinase kinase 3/6 and MAPKAP-2 occurs only upon growth factor withdrawal in primary erythroid progenitors. Moreover, our data indicate that activation of p38alpha does not induce apoptosis or promote proliferation of erythroid progenitors. On the other hand, under steady-state culture conditions, both p38alpha and p38delta isoforms are increasingly phosphorylated activated in the terminal phase of differentiation. This increased phosphorylation/activity was accompanied by up-regulation of heat shock protein 27 phosphorylation. Finally, we demonstrate that tumor necrosis factor alpha, an inflammatory cytokine that is modulated by p38alpha, is expressed by differentiating erythroblasts and inhibition of p38alpha or tumor necrosis factor alpha results in reduction in differentiation. Taken together, our data demonstrate that both p38alpha and delta isoforms function to promote the late-stage differentiation of primary erythroid progenitors and are likely to be involved in functions related to erythrocyte membrane remodeling and enucleation.

Potential for TRAIL as a Therapeutic Agent in Ovarian Cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to induce apoptosis, otherwise known as programmed cell death, in many malignant cells without any known detrimental effects to normal cells. These aspects of TRAIL indicate the potential of TRAIL as a therapeutic agent in cancer. Ovarian cancer remains the deadliest gynecologic malignancy and is the fourth leading cause of death due to cancer in women. However, it has been shown in studies that ovarian cancer cells are sensitive to TRAIL-induced cell death when treated with TRAIL alone or in combination with chemotherapeutic agents. TRAIL signals through two death receptors, TRAIL-R1 and TRAIL-R2, to induce apoptosis. TRAIL also binds to two other cell surface receptors, TRAIL-R3 and TRAIL-R4, which do not have intracellular death domains and therefore do not transmit the apoptotic signal upon ligation with TRAIL. It has been shown that a chemokine, interleukin-8 (IL-8), may play a role in ovarian tumor progression due to its elevated presence in the fluid surrounding ovarian cancer tissues. Possible roles for IL-8 in ovarian tumorigenesis include angiogenesis and metastasis. Because the mechanism of regulation for TRAIL-induced apoptosis needs to be clarified, the role of IL-8 in TRAIL-induced apoptosis of ovarian cancer cells was studied. Results showed that the presence of IL-8 regulates cell-surface expression of TRAIL receptors in ovarian cancer cell lines in vitro. There may be a role for the p38 mitogen-activated protein kinase (MAPK) pathway in TRAIL-induced apoptosis of ovarian cancer cell.

Suppression by p38 MAP Kinase Inhibitors (Pyridinyl Imidazole Compounds) of Ah Receptor Target Gene Activation by 2,3,7,8-Tetrachlorodibenzo-p-dioxin and the Possible Mechanism

Cytochrome P-450 1A1 (CYP1A1) is known to be induced by aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), through activation of the aryl hydrocarbon receptor (AhR). We found that p38 MAP kinase inhibitors (SB203580 and SB202190; 40 microm each; pyridinyl imidazole compounds) suppressed CYP1A1-mRNA induction by TCDD (2 nm) in mouse hepatoma Hepa-1 cells and in human hepatoma HepG2 cells, and also suppressed CYP1B1-mRNA induction by TCDD (2 nm) in human breast adenocarcinoma MCF7 cells. An analogue compound, SB202474, which does not inhibit p38 MAP kinase, also suppressed CYP1A1-mRNA induction by TCDD. Moreover, overexpression of a dominant-negative gene for p38 MAP kinase in Hepa-1 cells did not suppress Cyp1a1 reporter gene induction by TCDD. Therefore, the suppression of Cyp1a1 transcription by pyridinyl imidazole compounds is not because of their inhibition of p38 MAP kinase activity. Because SB203580 did not inhibit in vitro AhR transformation by TCDD, this compound was not acting as a simple AhR antagonist. SB203580 decreased TCDD-induced histone acetylation levels in the region of the Cyp1a1 gene promoter, especially around the TATA box sequence. This result suggests the possibility that pyridinyl imidazole compounds suppress the recruitment of some co-activator that has the histone acetyltransferase activity necessary for CYP1A1-mRNA transcription.

Involvement of p42/p44 MAPK, JNK, and NF-?B in IL-1?-induced ICAM-1 expression in human pulmonary epithelial cells

Interleukin-1beta (IL-1beta) has been shown to induce the expression of intercellular adhesion molecule-1 (ICAM-1) on airway epithelial cells and contributes to inflammatory responses. However, the mechanisms regulating ICAM-1 expression by IL-1beta in human A549 cells was not completely understood. Here, the roles of mitogen-activated protein kinases (MAPKs) and NF-kappaB pathways for IL-1beta-induced ICAM-1 expression were investigated in A549 cells. IL-1beta induced expression of ICAM-1 protein and mRNA in a time- and concentration-dependent manner. The IL-1beta induction of ICAM-1 mRNA and protein were partially inhibited by U0126 and PD98059 (specific inhibitors of MEK1/2) and SP600125 [a specific inhibitor of c-Jun-N-terminal kinase (JNK)]. U0126 was more potent than other inhibitors to attenuate IL-1beta-induced ICAM-1 expression. Consistently, IL-1beta stimulated phosphorylation of p42/p44 MAPK and JNK which was attenuated by pretreatment with U0126 or SP600125, respectively. Moreover, transfection with dominant negative mutants of MEK1/2 (MEK K97R) or ERK2 (ERK2 K52R) also attenuated IL-1beta-induced ICAM-1 expression. The combination of PD98059 and SP600125 displayed an additive effect on IL-1beta-induced ICAM-1 gene expression. IL-1beta-induced ICAM-1 expression was almost completely blocked by a specific NF-kappaB inhibitor helenalin. Consistently, IL-1beta stimulated translocation of NF-kappaB into the nucleus and degradation of IkappaB-alpha which was blocked by helenalin, U0126, or SP600125. Taken together, these results suggest that activation of p42/p44 MAPK and JNK cascades, at least in part, mediated through NF-kappaB pathway is essential for IL-1beta-induced ICAM-1 gene expression in A549 cells. These results provide new insight into the mechanisms of IL-1beta action that cytokines may promote inflammatory responses in the airway disease.

Distinctive regulation and function of PI 3K/Akt and MAPKs in doxorubicin-induced apoptosis of human lung adenocarcinoma cells

Regulation and function of PI 3K/Akt and mitogen-activated protein kinases (MAPKs) in doxorubicin-induced cell death were investigated in human lung adenocarcinoma cells. Doxorubicin induced dose-dependent apoptosis of human lung adenocarcinoma NCI-H522 cells. Prior to cell death, both Akt and the MAPK family members (MAPKs: ERK1/2, JNK, and p38) were activated in response to the drug treatment. The kinetics of the inductions for Akt and MAPKs are, however, distinct. The activation of Akt was rapid and transient, activated within 30 min of drug addition, then declined after 3 h, whereas the activations of three MAPKs occurred later, 4 h after addition of the drug and sustained until cell death occurred. Inhibition of PI 3K/Akt activation had no effect on MAPKs' activation, suggesting that the two pathways are independently activated in response to the drug treatment. Inhibition of PI 3K/Akt and p38 accelerated and enhanced doxorubicin-induced cell death. On the contrary, inhibition of ERK1/2 or JNK had no apparent effect on the cell death. Taken together, these results suggest that PI 3K/Akt and MAPKs signaling pathways are all activated, but with distinct mechanisms, in response to doxorubicin treatment. Activation of PI 3K/Akt and p38 modulates apoptotic signal pathways and inhibits doxorubicin-induced cell death. These responses of tumor cells to cancer drug treatment may contribute to their drug resistance. Understanding of the mechanism and function of the responses will be beneficial for the development of novel therapeutic approaches for improvement of drug efficacy and circumvention of drug resistance.

p38 MAP kinase activation mediates gamma-globin gene induction in erythroid progenitors

OBJECTIVE

Our goal was to determine the role of p38 mitogen-activated protein kinase (MAPK) signaling in fetal hemoglobin (HbF) induction. Two histone deacetylase inhibitors (HDAIs), sodium butyrate (NB), and trichostatin (TSA) and hemin were analyzed. In addition, the effect of direct activation of p38 MAPK on gamma-globin gene activity was studied.

METHOD

Primary erythroid progenitors derived from peripheral blood mononuclear cell and K562 erythroleukemia cells were analyzed. Cells were grown in NB, TSA, hemin, or anisomycin either alone or in the presence of the p38 MAPK inhibitor SB203580. The effects of the various treatments on gamma-globin RNA, HbF, and phosphorylated p38 MAPK levels were measured by RNase protection assay, alkaline denaturation, and Western blot analysis, respectively. A K562 stable line overexpressing constitutively active p38 MAPK was established using MAPK kinase kinase 3 (MKK3) and MKK6, the immediate upstream activators of p38. The direct effect of p38 MAPK overexpression on gamma-globin mRNA synthesis was analyzed.

RESULTS

NB and TSA activated p38 MAPK and increased gamma-globin mRNA levels in K562 cells and primary erythroid progenitors. Pretreatment with SB203580 blocked p38 MAPK and gamma-globin gene activation. In contrast, no change in p38 activity was observed with hemin inductions. Direct activation of p38 by anisomycin or constitutive overexpression also increased gamma-globin mRNA in the absence of HbF inducers in wild-type K562 cells and in the MKK stable lines.

CONCLUSION

This study supports a novel role for p38 MAPK in gamma-globin regulation in human erythroid progenitors.

Mitogenic signaling pathways in airway smooth muscle

Increased airway smooth muscle mass has been demonstrated in patients with asthma, bronchopulmonary dysplasia and most recently, cystic fibrosis. These observations emphasize the need for further knowledge of the events involved in airway smooth muscle mitogenesis and hypertrophy. Workers in the field have developed cell culture systems involving tracheal and bronchial myocytes from different species. An emergent body of literature indicates that mutual signal transduction pathways control airway smooth muscle cell cycle entry across species lines. This article reviews what is known about mitogen-activated signal transduction in airway myocytes. The extracellular signal regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI 3-kinase) pathways appear to be key positive regulators of airway smooth muscle mitogenesis; recent studies have also demonstrated specific roles for reactive oxygen and the JAK/STAT pathway. It is also possible that growth factor stimulation of airway smooth muscle concurrently elicits signaling through negative regulatory intermediates such as p38 mitogen-activated protein (MAP) kinase and protein kinase C (PKC) delta, conceivably as a defense against extreme growth.

Effect of OFR and [Ca2+]i on the activation of p38 MAPK in isolated rabbit liver during cold preservation and reperfusion period

AIM

To study the effect of OFR (oxygen-derieved free radicals) and calcium on the activation of p38 MAPK in isolated rabbit liver during cold preservation and reperfusion period.

METHODS

Based on the cold preservation-reperfusion model of isolated rabbit liver, isolated livers were divided into 4 groups according to the concentration of allopurinol or verapamil in the preservation solution. Liver tissue samples were harvested at the time points of before cold preservation, at the end of cold preservation, and during reperfusion period (5 min, 10 min, 60 min, 120 min). The phosphorylation level of p38MAPK and its activity in liver tissue were detected by Western-Blotting and immunoprecipitation respectively. The content of OFR and concentration of intracellular calciumion ([Ca²⁺]_i) were also measured by the corresponding method.

RESULTS

The content of OFR was increased to its peak value at 5 min during reperfusion period, the difference among the four groups was significant (groups A, B, C, D: 2.32±0.22, 1.82±0.15, 1.63±0.11, 1.29±0.10, P<0.05, t = 2.57). At 10 min during reperfusion period, the phosphorylation level and its activity of p38MAPK reached its peak value, and there was significant difference among the four groups (Groups A, B, C, D: p38MAPK phosphorylation level (76.2±7.0, 61.4±5.9, 47.3±2.5, 37.7±3.0, P<0.05, t = 2.61.Groups A, B, C, D: p38MAPK activity) 82.7±6.8, 69.7±5.2, 54.5±5.5, 41.2±3.1, P<0.05, t = 2.61. Groups A, E, F, G: p38MAPK phosphorylation level (80.3±8.7, 63.3±4.2, 50.4±5.6, 39.2±5.7, P<0.05, t = 2.61. Groups A, E, F, G: p38MAPK activity (80.8±8.9, 66.7±4.2, 53.7±4.1, 39.4±5.5, P<0.05, t = 2.61). The peak value of OFR content and [Ca²⁺]_i was significantly and positively correlated with the peak value of p38MAPK phosphorylation level and activity (P<0.05, R_OFR = 0.976, R_Ca = 0.970).

CONCLUSION

Allopurinol can significantly inhibit the OFR content of isolated liver tissues while verapamil can significantly inhibit the overload of Ca²⁺ concentration of isolated liver cells. The OFR content and overload of intracellular calciumion concentration are closely related with p38MAPK activation during cold preservation and reperfusion period. So activation of p38MAPK signal pathway may be an important mechanism of OFR and Ca²⁺ , which play a critical role in the ischemia-reperfusion injury of donor liver.

p38gamma MAPK regulation of glucose transporter expression and glucose uptake in L6 myotubes and mouse skeletal muscle

Skeletal muscle expresses at least three p38 MAPKs (alpha, beta, gamma). However, no studies have examined the potential regulation of glucose uptake by p38gamma, the isoform predominantly expressed in skeletal muscle and highly regulated by exercise. L6 myotubes were transfected with empty vector (pCAGGS), activating MKK6 (MKK6CA), or p38gamma-specific siRNA. MKK6CA-transfected cells had higher rates of basal 2-deoxy-d-[3H]glucose (2-DG) uptake (P < 0.05) but lower rates of 2,4-dinitrophenol (DNP)-stimulated glucose uptake, an uncoupler of oxidative phosphorylation that operates through an insulin-independent mechanism (P < 0.05). These effects were reversed when MKK6CA cells were cotransfected with p38gamma-specific siRNA. To determine whether the p38gamma isoform is involved in the regulation of contraction-stimulated glucose uptake in adult skeletal muscle, the tibialis anterior muscles of mice were injected with pCAGGS or wild-type p38gamma (p38gammaWT) followed by intramuscular electroporation. Basal and contraction-stimulated 2-DG uptake in vivo was determined 14 days later. Overexpression of p38gammaWT resulted in higher basal rates of glucose uptake compared with pCAGGS (P < 0.05). Muscles overexpressing p38gammaWT showed a trend for lower in situ contraction-mediated glucose uptake (P = 0.08) and significantly lower total GLUT4 levels (P < 0.05). These data suggest that p38gamma increases basal glucose uptake and decreases DNP- and contraction-stimulated glucose uptake, partially by affecting levels of glucose transporter expression in skeletal muscle. These findings are consistent with the hypothesis that activation of stress kinases such as p38 are negative regulators of stimulated glucose uptake in peripheral tissues.

MAPK pathways mediate hyperoxia-induced oncotic cell death in lung epithelial cells

Cell injury and cell death of pulmonary epithelium plays an important role in the pathogenesis of acute lung injury in animals exposed to prolonged hyperoxia. The aim of this study was to decipher the molecular mechanisms modulating cell death induced by hyperoxia in lung epithelium. Cell death is thought to be either apoptotic, with shrinking phenotypes and activated caspases, or oncotic, with swelling organelles. Exposure to 95% O2 (hyperoxia) induced cell death of MLE-12 cells with cellular as well as nuclear swelling, cytosolic vacuolation, and loss of mitochondrial structure and enzyme function. Neither elevated caspase-3 activity nor phosphatidylserine translocation were detected, suggesting that in hyperoxia, MLE-12 cells die via oncosis rather than apoptosis. In addition, hyperoxia triggered a sustained activation of the transcription factor AP-1, as well as mitogen-activated protein kinase (MAPK) family members p38 and JNK. Importantly, survival of MLE-12 cells in hyperoxia was significantly enhanced when either AP-1, p38, or JNK activation was inhibited by either specific inhibitors or dominant negative DNA constructs, indicating that in lung epithelial cells hyperoxia induces a program-driven oncosis, involving AP-1, JNK, and p38 MAPK. Interestingly, hydrogen peroxide-induced oxidative apoptosis of MLE-12 cells, with a shrinking nuclear morphology and activated caspase-3 activity, is also mediated by AP-1, JNK, and p38. Therefore, our data indicate that although they have divergent downstream events, oxidative oncosis and apoptosis share upstream JNK/p38 and AP-1 pathways, which could be used as potential targets for reducing hyperoxic inflammatory lung injury.

Indole-based heterocyclic inhibitors of p38alpha MAP kinase: designing a conformationally restricted analogue

p38alpha Mitogen Activated Protein Kinase (MAP kinase) is an intracellular soluble serine threonine kinase. p38alpha kinase is activated in response to cellular stresses, growth factors and cytokines such as interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha). The central role of p38alpha activation in settings of both chronic and acute inflammation has led efforts to find inhibitors of this enzyme as possible therapies for diseases such as rheumatoid arthritis, where p38alpha activation is thought to play a causal role. Herein, we report structure-activity relationship studies on a series of indole-based heterocyclic inhibitors that led to the design and identification of a new class of p38alpha inhibitors.

Nuclear factor of activated T cells c is a target of p38 mitogen-activated protein kinase in T cells

p38 mitogen activated protein kinase (MAPK) is essential for T-cell activation. Here we demonstrated that nuclear factor of activated T cells (NFAT) is a direct target of p38 MAPK. Inhibition of p38 MAPK led to selective inactivation of NFAT in T cells. We further linked a strict requirement of p38 MAPK to activation of NFATc. A stimulatory effect of p38 MAPK on at least four other stages of NFATc activation was found. First, the p38 MAPK cascade activated the NFATc promoter and induced the transcription of NFATc mRNA. Second, p38 MAPK mildly increased the mRNA stability of NFATc. Third, p38 MAPK enhanced the translation of NFATc mRNA. Fourth, p38 MAPK promoted the interaction of NFATc with the coactivator CREB-binding protein. In contrast, p38 MAPK moderately enhanced the expulsion of NFATc from the nucleus in T cells. Therefore, p38 MAPK has opposite effects on different stages of NFATc activation. All together, the overall effect of p38 MAPK on NFATc in T cells is clear activation.

p38 MAP kinases: key signalling molecules as therapeutic targets for inflammatory diseases

The p38 MAP kinases are a family of serine/threonine protein kinases that play important roles in cellular responses to external stress signals. Since their identification about 10 years ago, much has been learned of the activation and regulation of the p38 MAP kinase pathways. Inhibitors of two members of the p38 family have been shown to have anti-inflammatory effects in preclinical disease models, primarily through the inhibition of the expression of inflammatory mediators. Several promising compounds have also progressed to clinical trials. In this review, we provide an overview of the role of p38 MAP kinases in stress-activated pathways and the progress towards clinical development of p38 MAP kinase inhibitors in the treatment of inflammatory diseases.

Angiogenesis in collagen I requires alpha2beta1 ligation of a GFP*GER sequence and possibly p38 MAPK activation and focal adhesion disassembly

Angiogenesis depends on proper collagen biosynthesis and cross-linking, and type I collagen is an ideal angiogenic scaffold, although its mechanism is unknown. We examined angiogenesis using an assay wherein confluent monolayers of human umbilical vein endothelial cells were overlain with collagen in a serum-free defined medium. Small spaces formed in the cell layer by 2 h, and cells formed net-like arrays by 6-8 h and capillary-like lumens by 24 h. Blocking of alpha2beta1, but not alpha1 or alpha(v)beta3 integrin function halted morphogenesis. We found that a triple-helical, homotrimeric peptide mimetic of a putative alpha2beta1 binding site: alpha1(I)496-507 GARGERGFP*GER (where single-letter amino acid nomenclature is used, P* = hydroxyproline) inhibited tube formation, whereas a peptide carrying another putative site: alpha1(I)127-138 GLP*GERGRP*GAP* or control peptides did not. A chemical inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), SB202190, blocked tube formation, and p38 MAPK activity was increased in collagen-treated cultures, whereas targeting MAPK kinase (MEK), focal adhesion kinase (FAK), or phosphatidylinositol 3-kinase (PI3K) had little effect. Collagen-treated cells had fewer focal adhesions and 3- to 5-fold less activated FAK. Thus capillary morphogenesis requires endothelial alpha2beta1 integrin engagement of a single type I collagen integrin-binding site, possibly signaling via p38 MAPK and focal adhesion disassembly/FAK inactivation.

Regulation of 90-kilodalton ribosomal S6 kinase phosphorylation in the rat pineal gland

In this study we investigated diurnal changes in the activation state of the 90-kDa ribosomal S6 kinase (p90RSK) in the rat pineal gland. In animals housed under a lighting regimen with 12 h of light, we found an increase in phosphorylated p90RSK during the dark phase, and this increase was abolished by treatment with propranolol or continuous exposure to light. To determine the intracellular mechanism involved, rat pinealocytes were treated with norepinephrine. Norepinephrine caused a parallel increase in phosphorylated p42/44 MAPK (p42/44(MAPK)) and p90RSK that was reduced by prazosin or propranolol, indicating involvement of both alpha(1)- and beta-adrenergic receptors. Treatment with dibutyryl cGMP, 4beta-phorbol 12-myristate 13-acetate, or ionomycin mimicked norepinephrine-stimulated p90RSK phosphorylation, whereas dibutyryl cAMP caused a decrease in p90RSK phosphorylation. Inhibition of p42/44(MAPK) activation by UO126 was effective in reducing norepinephrine-stimulated p90RSK phosphorylation. Moreover, UO126 had an inhibitory effect on norepinephrine-stimulated arylalkyl-N-acetyltransferase activity. These results indicate that the adrenergically regulated nocturnal increase in p90RSK phosphorylation is mainly mediated through a cGMP-->p42/44(MAPK)-dependent mechanism.

cFLIP-L inhibits p38 MAPK activation: an additional anti-apoptotic mechanism in bile acid-mediated apoptosis

In cholestasis, toxic bile acids accumulate within the liver inducing hepatocyte apoptosis, which exacerbates liver injury. Although bile acids activate both death receptors and mitogen-activated kinase (MAPK) pathways, the mechanistic link between death receptor signaling and MAPK activation in bile acid apoptosis remains unclear. The aim of this study was to ascertain if MAPKs contribute to bile acid cytotoxicity. Although deoxycholate induced apoptosis and activated all three classic mediators of the MAPK pathways including JNK 1/2, p38, and p42/44, only p38 MAPK inhibition attenuated apoptosis. Suppressing FADD expression with siRNA or employing a caspase inhibitor, zVAD-fmk, did not block p38 MAPK activation suggesting its activation was not death receptor-dependent. Unexpectedly, expression of cFLIP-L in a stably transfected cell line blocked apoptosis and p38 MAPK phosphorylation. Based on these data we postulated a direct effect of cFLIP on p38 MAPK activation. The nonphosphorylated but not the phosphorylated/active form of p38 MAPK co-immunoprecipitated with cFLIP-L. In reverse immunoprecipitation experiments, cFLIP-L long but not cFLIP-S co-immunoprecipitate with p38 MAPK. In conclusion, these data suggest that cFLIP-L exerts its anti-apoptotic activity, in part, by inhibiting p38 MAPK activation, an additional anti-apoptotic effect for this protein.

Inhibition of tumor necrosis factor-alpha-dependent cardiomyocyte apoptosis by metallothionein

Myocardial cell death is an important cellular event of heart failure. Tumor necrosis factor-alpha (TNF) accumulates in the failing heart and causes myocyte apoptosis, but the mechanism of this action is unclear. This study was undertaken to examine the relationship between TNF-induced cardiomyocyte apoptosis and activation of p38 mitogen-activated protein kinase (MAPK) through oxidative stress. Primary cultures of neonatal cardiomyocytes isolated from transgenic mouse hearts that overexpress metallothionein (MT) as well as cardiomyocytes isolated from wild-type mice were used. The treatment of wildtype cardiomyocytes with TNF at 10 ng/mL induced apoptosis, as detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and confirmed by Annexin V-fluorescein isothiocyanate binding. The apoptotic effect of TNF was significantly inhibited in the MT-overexpressing cardiomyocytes. Corresponding to the apoptotic effect, TNF at 10 ng/mL caused rapid phosphorylation of p38 MAPK in wild-type cardiomyocytes. The activation of p38 MAPK was further confirmed by an in vivo experiment treating the mice with TNF and measuring p38 MAPK activity using an immune complex kinase assay. The activation of p38 MAPK was not observed in the MT-overexpressing cardiomyocytes either in vitro or in vivo. Importantly, TNF-induced accumulation of reactive oxygen species was dramatically reduced in the MT-overexpressing cardiomyocytes as determined by a carboxy-H(2)-DCFDA staining method. This study thus suggests that p38 MAPK activation is likely involved in TNFinduced cardiomyocyte apoptosis, which is also related to reactive oxygen species accumulation.

Renal Abnormalities in Mice Caused by Insufficiency of p38α

p38MAP kinase (p38) is activated by hypertonicity and has been implicated to play a pivotal role in the renal system in survival under hypertonic conditions, both in vitro and in vivo. Although there are many aspects of the molecular events via the p38 pathway, its contribution to renal physiology and pathophysiology remains unclear. To elucidate the physiological relevance of p38 in renal function, we performed histochemical and biochemical characterization of p38alpha+/- mice. Although p38alpha+/- mice appeared normal, they showed 24% higher water intake (P < 0.05) and 16% higher kidney weight to total body weight ratio (P < 0.01) at 21 weeks of age. Histological examination of the kidney showed abnormalities such as dilation of proximal convoluted tubules, vacuolar degeneration, focal interstitial fibrosis, and inflammation and enlargement of Bowman's capsule with advancing age. Taken together, these results suggest that p38alpha plays an important role in the structural and functional maintenance of the normal kidney and its insufficiency causes renal abnormalities.

S100B inhibits myogenic differentiation and myotube formation in a RAGE-independent manner

S100B is a Ca(2+)-modulated protein of the EF-hand type with both intracellular and extracellular roles. S100B, which is most abundant in the brain, has been shown to exert trophic and toxic effects on neurons depending on the concentration attained in the extracellular space. S100B is also found in normal serum, and its serum concentration increases in several nervous and nonnervous pathological conditions, suggesting that S100B-expressing cells outside the brain might release the protein and S100B might exert effects on nonnervous cells. We show here that at picomolar to nanomolar levels, S100B inhibits myogenic differentiation of rat L6 myoblasts via inactivation of p38 kinase with resulting decrease in the expression of the myogenic differentiation markers, myogenin, muscle creatine kinase, and myosin heavy chain, and reduction of myotube formation. Although myoblasts express the multiligand receptor RAGE, which has been shown to transduce S100B effects on neurons, S100B produces identical effects on myoblasts overexpressing either full-length RAGE or RAGE lacking the transducing domain. This suggests that S100B affects myoblasts by interacting with another receptor and that RAGE is not the only receptor for S100B. Our data suggest that S100B might participate in the regulation of muscle development and regeneration by inhibiting crucial steps of the myogenic program in a RAGE-independent manner.

Review article: mitogen-activated protein kinases in chronic intestinal inflammation - targeting ancient pathways to treat modern diseases

Conventional treatment of chronic inflammatory disorders, including inflammatory bowel diseases, employs broad-range anti-inflammatory drugs. In order to reduce the side-effects and increase the efficacy of treatment, several strategies have been developed in the last decade to interfere with intercellular and intracellular inflammatory signalling processes. The highly conserved mitogen-activated protein kinase pathways regulate most cellular processes, particularly defence mechanisms such as stress reactions and inflammation. In this review, we provide an overview of the current knowledge of the specificity and interconnection of mitogen-activated protein kinase pathways, their functions in the gut immune system and published and ongoing studies on the role of mitogen-activated protein kinases in inflammatory bowel disease. The development of mitogen-activated protein kinase inhibitors and their use for the therapy of inflammatory disorders is a paradigm of the successful bridging of the gap between basic research and clinical practice.

Map kinase signaling pathways and hematologic malignancies

Mitogen-activated protein (Map) kinases are widely expressed serine-threonine kinases that mediate important regulatory signals in the cell. Three major groups of Map kinases exist: the p38 Map kinase family, the extracellular signal-regulated kinase (Erk) family, and the c-Jun NH2-terminal kinase (JNK) family. The members of the different Map kinase groups participate in the generation of various cellular responses, including gene transcription, induction of cell death or maintenance of cell survival, malignant transformation, and regulation of cell-cycle progression. Depending on the specific family isoform involved and the cellular context, Map kinase pathways can mediate signals that either promote or suppress the growth of malignant hematopoietic cells. Over the last few years, extensive work by several groups has established that Map kinase pathways play critical roles in the pathogenesis of various hematologic malignancies, providing new molecular targets for future therapeutic approaches. In this review, the involvement of various Map kinase pathways in the pathophysiology of hematologic malignances is summarized and the clinical implications of the recent advances in the field are discussed.

Prior exercise increases basal and insulin-induced p38 mitogen-activated protein kinase phosphorylation in human skeletal muscle

We have examined the effects of insulin on p38 mitogen-activated protein kinase (MAPK) phosphorylation in human skeletal muscle and the effects of prior exercise hereon. Seven men performed 1-h one-legged knee extensor exercise 3 h before the initiation of a 100-min euglycemic-hyperinsulinemic (600 pmol/l) clamp. Glucose uptake across the legs was measured with the leg balance technique, and muscle biopsies were obtained from the rested and exercised vastus lateralis before and during insulin infusion. Net glucose uptake during the clamp was approximately 50% higher (P < 0.05) in the exercised leg than in the rested leg. Insulin induced a modest sustained 1.2- and 1.3-fold increase (P < 0.05) in p38 MAPK phosphorylation in the rested and exercised legs, respectively. However, p38 phosphorylation was approximately 50% higher (P < 0.05) in the exercised compared with the rested leg before and during insulin infusion. We conclude that a physiological concentration of insulin causes modest but sustained activation of the p38 MAPK pathway in human skeletal muscle. Furthermore, the stimulatory effect of exercise on p38 phosphorylation is persistent for at least 3 h after exercise and remains evident during subsequent insulin stimulation. Because p38 MAPK has been suggested to play a necessary role in activation of GLUT-4 at the cell surface, the present data may suggest a putative role of p38 MAPK in the increased insulin sensitivity of skeletal muscle after exercise.

Role of Smad4 on TGF-beta-induced extracellular matrix stimulation in mesangial cells

BACKGROUND

The best characterized signaling pathway employed by transforming growth factor-beta (TGF-beta) is the Smad pathway; however, its role in matrix production in mesangial cells is unclear. We focused on Smad4, as Smad4 is essential for the activation of Smad-dependent target genes.

METHODS

To investigate the function of Smad4 in extracellular matrix (ECM) production, we generated several stably transfected mesangial cell lines (MMC) that have a deletion in the linker region (Smad4 Delta M4: Delta 275-322) or have a deletion in MH1 of Smad4 (Smad4N4: Delta 1-136). The ECM genes, alpha1 type I collagen (COL1A1), plasminogen activator inhibitor-1 (PAI-1) and fibronectin (FN) were assessed in wild-type mesangial cells and stably transfected Smad4-DN cell lines in the absence and presence of TGF-beta.

RESULTS

As compared to wild-type MMC that had a 10.8-fold stimulation of TGF-beta-induced p3TP-Lux activity, MMC stably transfected with Smad4 Delta M4 and Smad4N4 had only a 2.0-fold and 1.3-fold stimulation, respectively, indicating that they had dominant-negative effects on TGF-beta signaling. Basal and TGF-beta-induced COL1A1 expression in Smad4 dominant-negative cells were dramatically reduced to very low levels. The early (2 hours) TGF-beta-induced PAI-1 mRNA expression was inhibited; however, the sustained (24 to 48 hours) TGF-beta-induced expression was not affected in Smad4 dominant-negative cells. For FN, TGF-beta-induced expression was maintained in Smad4-dominant negative cells.

CONCLUSION

These results indicate that Smad4 is essential for basal and TGF-beta-induced COL1A1 expression, and contributes to the early, but not sustained TGF-beta-induced PAI-1 expression in mesangial cells. However, TGF-beta-induced FN expression is independent of Smad4. In conclusion, Smad4 has a discriminate effect in mediating specific ECM molecules stimulated by TGF-beta in mesangial cells.

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.

Cytokine-suppressive anti-inflammatory drugs (CSAIDs) inhibit invasion and MMP-1 production of ovarian carcinoma cells

The development of therapeutic strategies for inhibition of peritoneal dissemination and invasion would be central for the treatment of ovarian carcinoma. In the microenvironment of ovarian carcinomas, various inflammatory cytokines like tumor necrosis factor alpha (TNF-alpha) are present. In this study we investigated the role of inflammatory cytokines in the regulation of invasion of SKOV-3 ovarian carcinoma cells in-vitro. Treatment of cells with TNF-alpha or interleukin 1beta (IL-1beta) lead to increased phosphorylation of the stress-activated p38 mitogen-activated protein kinase (p38MAPK). Furthermore, TNF-alpha as well as IL-1beta stimulated matrigel invasion of tumor cells. An inhibitor of stress-activated protein kinase pathways, the cytokine-suppressive anti-inflammatory drug (CSAID) SB203580 inhibited invasion of cytokine-stimulated SKOV-3 cells. The MEK-1 inhibitor PD98059 similarly inhibited invasion of cytokine-stimulated cells, but to a lesser extent. Expression of mRNA and protein levels of matrix metalloproteinase-1 (MMP-1) by SKOV-3 cells could be stimulated by inflammatory cytokines and inhibited by SB203580, and partially also by PD98059. Our results show that CSAIDs reduce invasion and MMP expression of ovarian carcinoma cells. Further studies are required to investigate whether inhibition of cytokine-induced signal transduction may be of value in therapy of ovarian carcinomas in-vivo.

Transcriptional regulation of heme oxygenase-1 gene expression by MAP kinases of the JNK and p38 pathways in primary cultures of rat hepatocytes

Heme oxygenase-1 (HO-1) gene expression is induced by various oxidative stress stimuli including sodium arsenite. Since mitogen-activated protein kinases (MAPKs) are involved in stress signaling we investigated the role of arsenite and MAPKs for HO-1 gene regulation in primary rat hepatocytes. The Jun N-terminal kinase (JNK) inhibitor SP600125 decreased sodium arsenite-mediated induction of HO-1 mRNA expression. HO-1 protein and luciferase activity of reporter gene constructs with -754 bp of the HO-1 promoter were induced by overexpression of kinases of the JNK pathway and MKK3. By contrast, overexpression of Raf-1 and ERK2 did not affect expression whereas overexpression of p38alpha, beta, and delta decreased and p38gamma increased HO-1 expression. Electrophoretic mobility shift assays (EMSA) revealed that a CRE/AP-1 element (-668/-654) bound c-Jun, a target of the JNK pathway. Deletion or mutation of the CRE/AP-1 obliterated the JNK- and c-Jun-dependent up-regulation of luciferase activity. EMSA also showed that an E-box (-47/-42) was bound by a putative p38 target c-Max. Mutation of the E-box strongly reduced MKK3, p38 isoform-, and c-Max-dependent effects on luciferase activity. Thus, the HO-1 CRE/AP-1 element mediates HO-1 gene induction via activation of JNK/c-Jun whereas p38 isoforms act through a different mechanism via the E-box.

Induction of cyclooxygenase-2 by lipopolysaccharide in canine tracheal smooth muscle cells: involvement of p42/p44 and p38 mitogen-activated protein kinases and nuclear factor-kappaB pathways

Lipopolysaccharide (LPS) was found to induce inflammatory responses in the airways and exerted as a potent stimulus for PG synthesis. This study was to determine the mechanisms of LPS-enhanced cyclooxygenase (COX)-2 expression associated with PGE(2) synthesis in tracheal smooth muscle cells (TSMCs). LPS markedly increased the expression of COX-2 and release of PGE(2) in a time- and concentration-dependent manner, whereas COX-1 remained unaltered. Both the expression of COX-2 and the generation of PGE(2) in response to LPS were attenuated by a tyrosine kinase inhibitor genistein, a phosphatidylcholine-phospholipase C inhibitor D609, a phosphatidylinositol-phospholipase C inhibitor U73122, protein kinase C inhibitors, GF109203X and staurosporine, removal of Ca(2+) by addition of BAPTA/AM plus EGTA, and phosphatidylinositol 3-kinase (PI3-K) inhibitors, LY294002 and wortmannin. Furthermore, LPS-induced NF-kappaB activation correlated with the degradation of IkappaB-alpha, COX-2 expression, and PGE(2) synthesis, was inhibited by transfection with dominant negative mutants of NIK and IKK-alpha, but not by IKK-beta. LPS-induced COX-2 expression and PGE(2) synthesis were completely inhibited by PD98059 (an inhibitor of MEK1/2) and SB203580 (an inhibitor of p38 MAPK inhibitor), but these two inhibitors had no effect on LPS-induced NF-kappaB activation, indicating that NF-kappaB is activated by LPS independently of activation of p42/p44 MAPK and p38 MAPK pathways in TSMCs. Taken together, these findings suggest that the increased expression of COX-2 correlates with the release of PGE(2) from LPS-challenged TSMCs, at least in part, independently mediated through MAPKs and NF-kappaB signalling pathways. LPS-mediated responses were modulated by PLC, Ca(2+), PKC, tyrosine kinase, and PI3-K in these cells.

The p38 mitogen-activated protein kinase pathway and its role in interferon signaling

Interferons (IFNs) are pleiotropic cytokines that exhibit multiple biological effects on cells and tissues. IFN receptors are expressed widely in mammalian cells and virtually all different cell types express them on their surface. The Type I IFN receptor has a multichain structure, composed of at least two distinct receptor subunits, IFNalphaR1 and IFNalphaR2. Two Jak-kinases, Tyk-2 and Jak-1, associate with the different receptor subunits and are activated in response to IFNalpha or IFNbeta to regulate engagement of multiple downstream signaling cascades. These include the Stat-pathway, whose function is essential for transcriptional activation of IFN-sensitive genes, and the insulin receptor substrate pathway, which regulates downstream activation of the phosphatidyl-inositol-3' kinase. Members of the Map family of kinases are also activated by the Type I IFN receptor and participate in the generation of IFN signals. The p38 Map kinase pathway appears to play a very important role in the induction of IFN responses. p38 is rapidly activated during engagement of the Type I IFN receptor, and such an activation is regulated by the small G-protein Rac1, which functions as its upstream effector in a tyrosine kinase-dependent manner. The activated form of p38 regulates downstream activation of other serine kinases, notably MapKapK-2 and MapKapK-3, indicating the existence of Type I IFN-dependent signaling cascades activated downstream of p38. Extensive studies have shown that p38 plays a critical role in Type I IFN-dependent transcriptional regulation, without modifying activation of the Stat-pathway. It is now well established that the function of p38 is essential for gene transcription via ISRE or GAS elements, but has no effects on the phosphorylation of Stat-proteins, the formation of Stat-complexes, and their binding to the promoters of IFN-sensitive genes. As Type I IFNs regulate gene expression for proteins with antiviral properties, it is not surprising that pharmacological inhibition of the p38 pathway blocks induction of IFNalpha-antiviral responses. In addition, pharmacological inhibition of p38 abrogates the suppressive effects of Type I IFNs on normal human hematopoietic progenitors, indicating a critical role for this signaling cascade in the induction of the regulatory effects of Type I IFNs on hematopoiesis. p38 is also activated during IFNalpha-treatment of primary leukemia cells from patients with chronic myelogenous leukemia. Such activation is required for IFNalpha-dependent suppression of leukemic cell progenitor growth, indicating that this pathway plays a critical role in the induction of the antileukemic effects of IFNalpha.

p38 Mitogen-activated protein kinases on the body surface--a function for p38 delta

The p38 family of mitogen-activated protein kinases includes p38 alpha (SAPK2a, CSBP), p38 beta (SAPK2b), p38 delta (SAPK4), and p38 gamma (SAPK3/ERK6). p38 alpha and p38 beta are widely expressed p38 isoforms that are involved in regulation of cell proliferation, differentiation, development, and response to stress. Relatively less is known regarding the function of the p38 delta isoform. In this review, we discuss the role of the p38 alpha, p38 beta, and p38 gamma isoforms and then present recent findings that define a role for p38 delta as a regulator of differentiation-dependent gene expression in keratinocytes.

MAPK signal transduction pathway mediates agrin effects on neurite elongation in cultured hippocampal neurons

We have previously shown that agrin regulates the rates of axonal and dendritic elongation by modulating the expression of microtubule-associated proteins in cultured hippocampal neurons. However, the mechanisms by which agrin-induced signals are propagated to the nucleus where they can lead to the phosphorylation, and hence the activation, of transcription factors, are not known. In the present study, we identified downstream elements that play essential roles in the agrin-signaling pathway in developing central neurons. Our results indicate that agrin induces the combined activation of the extracellular signal-regulated kinases (ERK1/ERK2) and p38 in central neurons. In addition, they showed that PD98059 and SB202190, synthetic inhibitors of ERK1/ERK2 and p38 respectively, prevented the changes in the rate of neurite elongation induced by agrin in cultured hippocampal neurons. Collectively, these results suggest that agrin might modulate the expression of neuron-specific genes involved in neurite elongation by inducing CREB phosphorylation through the activation of the MAPK signal transduction pathway in cultured hippocampal neurons.

Characterization of apoptosis signal transduction pathways in HL-5 cardiomyocytes exposed to ischemia/reperfusion oxidative stress model

During ischemia/reperfusion (I/R), cardiomyocytes are exposed to sudden lack of nutrients and successively to radical oxygen species (ROS). In the present study, we used the HL-5 cardiac atrial myocyte cell line exposed to serum/glucose depletion added or not in H(2)O(2) to mimic ROS during ischemia, then replaced in their standard culture medium to simulate reperfusion. We investigated the effects of serum/glucose depletion combined or not to ROS exposure on AKT and MAP kinases activation to address the role of each event with respect to apoptosis. We demonstrate that serum/glucose depletion per se did not induce apoptosis when compared to ROS exposure. In particular, ROS recruited p38MAPK and JNK pathways. SB202190 preventing p38MAPK activity, partially protected HL-5 from apoptosis while blocking JNK, thanks to JNKI, further enhanced apoptosis. Blocking phosphatidylinositol (PI) 3-kinase with LY294002 or ERKs with U0126 was without consequence on apoptosis. Finally, BCL-2 and BCL-X(L/S) expression levels were analyzed in cells exposed to 1 h ischemia followed by 12-h reperfusion in the presence or not of SB202190; BCL-2, but not BCL-X(L/S), expression was decreased in ROS treated cells but SB202190 failed to restore BCL-2 level. Our data suggest that p38MAPK activation primarily mediates ROS-induced apoptosis while concomitant JNK activation would represent a scavenger pathway for cells trying to escape apoptosis.

Nitric oxide-induced epidermal growth factor-dependent phosphorylations in A431 tumour cells

Nitric oxide (NO*) strongly inhibits the proliferation of human A431 tumour cells. It also inhibits tyrosine phosphorylation of a 170-kDa band corresponding to the epidermal growth factor receptor (EGFR) and induces the phosphorylation at tyrosine residue(s) of a 58-kDa protein which we have denoted NOIPP-58 (nitric oxide-induced 58-kDa phosphoprotein). The NO*-induced phosphorylation of NOIPP-58 is strictly dependent on the presence of EGF. Phosphorylation of NOIPP-58 and inhibition of the phosphorylation of the band corresponding to EGFR are both cGMP-independent processes. We also demonstrate that the p38 mitogen-activated protein kinase (p38MAPK) pathway is activated by NO* in the absence and presence of EGF, whereas the activity of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and the c-Jun N-terminal kinase 1/2 (JNK1/2) pathways are not significantly affected or are slightly decreased, respectively, on addition of this agent. Moreover, we show that the p38MAPK inhibitor, SB202190, induces rapid vanadate/peroxovanadate-sensitive dephosphorylation of prephosphorylated EGFR and NOIPP-58. We propose that the dephosphorylation of both NOIPP-58 and EGFR are mediated by a p38MAPK-controlled phosphotyrosine-protein phosphatase (PYPP). Activation of the p38MAPK pathway during nitrosative stress probably prevents the operation of this PYPP, allowing NOIPP-58, and in part EGFR, to remain phosphorylated and therefore capable of generating signalling events.

Grape seed extract inhibits EGF-induced and constitutively active mitogenic signaling but activates JNK in human prostate carcinoma DU145 cells: possible role in antiproliferation and apoptosis

A loss of functional androgen receptor and an enhanced expression of growth factor receptors and associated ligands are causal genetic events in prostate cancer (PCA) progression. These genetic alterations lead to an epigenetic mechanism where a feedback autocrine loop between membrane receptor and ligand (e.g. EGFR-TGFalpha) results in a constitutive activation of MAPK-Elk1-AP1-mediated mitogenic signaling in human PCA at an advanced and androgen-independent stage. We rationalized that inhibiting these epigenetic events could be useful in controlling advanced PCA growth. Recently, we found that grape seed extract (GSE), a dietary supplement rich in flavonoid procyanidins, inhibits advanced and androgen-independent human PCA DU145 cell growth in culture and nude mice. Here, we performed detailed mechanistic studies to define the effect of GSE on EGFR-Shc-MAPK-Elk1-AP1-mediated mitogenic signaling in DU145 cells. Pretreatment of serum-starved cells with GSE resulted in 70% to almost complete inhibition of EGF-induced EGFR activation and 50% to complete inhibition of Shc activation, which corroborated with a comparable decrease in EGF-induced Shc binding to EGFR. Conversely, EGF-induced ERK1/2 phosphorylation was inhibited only by lower doses of GSE; in fact, higher doses showed an increase. Additional studies showed that GSE alone causes a dose- and time-dependent increase in ERK1/2 phosphorylation in starved DU145 cells that is inhibited by an MEK1 inhibitor PD98059. Independent of this increase in ERK1/2 phosphorylation, GSE showed a strong inhibition of ERK1/2 kinase activity to Elk1 in both cellular and cell-free systems. GSE treatment of cells also inhibited both EGF-induced and constitutively active Elk1 phosphorylation and AP1 activation. GSE treatment also showed DNA synthesis inhibition in starved and EGF-stimulated cells as well as loss of cell viability and apoptotic death that was further increased by adding MEK1 inhibitor. Since GSE strongly induced apoptosis independent of its affect on an increase in phospho-ERK1/2, we hypothesized that apoptotic effect of GSE could be by other mechanism(s) including its effect on stress-associated MAPK, the JNK. Indeed, GSE-treated cells showed a strong and sustained increase in phospho-JNK1/JNK2 levels, JNK activity and phospho-cJun levels. An inhibition of GSE-induced JNK activation by a novel JNK inhibitor SP600125 resulted in a significant reversal of GSE-induced apoptotic death suggesting the involvement of JNK activation by GSE in its apoptosis response. Together, these results suggest that anticancer effects of GSE in PCA be mediated via impairment of EGFR-ERK1/2-Elk1-AP1-mediated mitogenic signaling and activation of JNK causing growth inhibition and apoptosis, respectively.

Enhanced sensitivity to cis-diamminedichloroplatinum(II) of a human carcinoma cell line with mutated p53 gene by cyclin-dependent kinase inhibitor p21(WAF1) expression

p53-mediated induction of p21(WAF1), a cyclin-dependent protein kinase inhibitor, is known to protect cancer cells from the cytotoxic effects of anti-cancer drugs or gamma-irradiation. Since the p53 gene is frequently inactivated in cancer cells, we examined whether p21(WAF1) expression may alter the sensitivity of cancer cells with mutated p53 gene to anti-cancer drugs. Cells of a colon cancer cell line DLD-1 were transfected with p21(WAF1) expression vector controlled by a tetracycline-repressable promoter and transfectants were cloned (Dp21-1). p21(WAF1) expression induced by removal of tetracycline from culture media repressed cell proliferation and resulted in altered cell shape, suggesting induction of differentiation. Dp21-1 cells with p21(WAF1) expression were more sensitive to cis-diamminedichloroplatinum(II) (CDDP) (IC(50) value, 10 microM) than those without p21(WAF1) expression (IC(50), 22 microM). Sensitivity to doxorubicin was not different between Dp21-1 cells with and without p21(WAF1) expression. DNA ladder formation was observed in Dp21-1 cells treated with CDDP, indicating that the enhanced sensitivity to CDDP involves apoptosis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cytosolic protein revealed that subunit protein bands with M(r) 55 kDa and 44 kDa were markedly increased in cells with p21(WAF1) expression. By immunoblotting, these proteins were identified as c-Jun N-terminal kinase (JNK) 2 and p38 mitogen-activated protein kinase (MAPK) delta, respectively, both of which are believed to be involved in apoptosis induction by CDDP. These results suggest that p21(WAF1) may enhance the sensitivity of colon cancer cells with mutated p53 gene to CDDP, possibly through the JNK and p38 MAPK pathways.

p38 isoforms have opposite effects on AP-1-dependent transcription through regulation of c-Jun. The determinant roles of the isoforms in the p38 MAPK signal specificity

p38 MAPK pathway signaling is known to participate in cell proliferation, apoptosis, and differentiation, in a manner dependent on the cellular context. The factors that determine the specific biological response in a given cell type, however, remain largely unknown. We report opposite effects of the p38 isoforms on regulation of AP-1-dependent activities by p38 activators MAPK kinase 6 (MKK6) and/or arsenite in human breast cancer cells. The p38beta isoform increases the activation of AP-1 transcriptional activities by MKK6 and/or arsenite, whereas p38gamma/p38delta inhibits or has no effect on the stimulation. The p38beta does so by increasing the levels of phosphorylated c-Jun, whereas the p38gamma and -delta isoforms may act by regulating the c-jun transcription. AP-1-dependent processes such as vitamin D receptor gene promoter activation and cellular proliferation were similarly activated by the p38beta or inhibited by the p38gamma and/or -delta isoforms. Whereas the human breast cancer cells express all four isoforms, mouse NIH 3T3 and EMT-6 cells express only some of the p38 family members, with p38beta higher in 3T3 cells but p38delta only detected in the EMT-6 line. Consistent with the positive and negative roles of p38beta and p38delta in AP-1 regulation, MKK6 stimulates AP-1-dependent transcription in NIH 3T3 but not EMT-6 cells. In support of a role of c-Jun regulation by p38 isoforms in determining AP-1 activity, the levels of endogenous c-Jun and its phosphorylated form on p38 activation are higher in NIH 3T3 cells. These results demonstrate the contrasting activities of the different p38 isoforms in transmitting the upstream signal to AP-1 and show that the expression profile of p38 isoforms determines whether the p38 signal pathway activates or inhibits AP-1-dependent processes.

Transforming growth factor-beta1 (TGF-beta)-induced apoptosis of prostate cancer cells involves Smad7-dependent activation of p38 by TGF-beta-activated kinase 1 and mitogen-activated protein kinase kinase 3

The inhibitory Smad7, a direct target gene for transforming growth factor-beta (TGF-beta), mediates TGF-beta1-induced apoptosis in several cell types. Herein, we report that apoptosis of human prostate cancer PC-3U cells induced by TGF-beta1 or Smad7 overexpression is caused by a specific activation of the p38 mitogen-activated protein kinase pathway in a TGF-beta-activated kinase 1 (TAK1)- and mitogen-activated protein kinase kinase 3 (MKK3)-dependent manner. Expression of dominant negative p38, dominant negative MKK3, or incubation with the p38 selective inhibitor [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole], prevented TGF-beta1-induced apoptosis. The expression of Smad7 was required for TGF-beta-induced activation of MKK3 and p38 kinases, and endogenous Smad7 was found to interact with phosphorylated p38 in a ligand-dependent manner. Ectopic expression of wild-type TAK1 promoted TGF-beta1-induced phosphorylation of p38 and apoptosis, whereas dominant negative TAK1 reduced TGF-beta1-induced phosphorylation of p38 and apoptosis. Endogenous Smad7 was found to interact with TAK1, and TAK1, MKK3, and p38 were coimmunoprecipitated with Smad7 in transiently transfected COS1 cells. Moreover, ectopically expressed Smad7 enhanced the coimmunoprecipitation of HA-MKK3 and Flag-p38, supporting the notion that Smad7 may act as a scaffolding protein and facilitate TAK1- and MKK3-mediated activation of p38.

Involvement of p38 mitogen-activated protein kinase in different stages of thymocyte development

Positive selection of thymocytes during T-cell development is mediated by T-cell receptor (TCR)-activated signals. For different mitogen-activated protein kinases (MAPKs) activated by TCR complex, a selective involvement of extracellular signal-regulated kinase, but not p38 MAPK, in positive selection has been suggested. Using transgenic mice with dominant-negative mutation of both MAP kinase kinase 3 (MMK3) and MKK6, we obtained mice with different extents of inhibition of p38 MAPK activation. Partial inhibition of p38 MAPK impaired CD4(-)CD8(-) thymocyte development and T-cell proliferation, but not positive selection. Interference with thymocyte positive selection was observed in mice with effective suppression of p38 MAPK. Our results suggest that, in addition to early thymocyte development, p38 is involved in positive selection.

Regulation of myeloid zinc finger protein 2A transactivation activity through phosphorylation by mitogen-activated protein kinases

The myeloid zinc finger protein (MZF)-2 is a C(2)H(2) zinc finger transcription factor that is expressed in myeloid cells and involved in the growth, differentiation, and tumorigenesis of myeloid progenitors. Here we describe a novel isoform of MZF-2, designated MZF-2A, and show that it is phosphorylated by the mitogen-activated protein (MAP) kinases. An in vitro phosphorylation experiment revealed that the transactivation domain (TAD) of MZF-2A was phosphorylated strongly by extracellular signal-regulated kinase (ERK) and phosphorylated weakly by p38 MAP kinase but not by Jun N-terminal kinase. Experiments using "add-back" mutants showed that three serine residues (Ser(257), Ser(275), and Ser(295)) in the TAD were phosphorylated in vitro by ERK. In myeloid LGM-1 cells, various extracellular stimuli induced the phosphorylation of these serine residues, which was differentially inhibited by the protein kinase inhibitors U0126 and SB203580. Substitution of these phosphorylation sites with alanines resulted in a strong enhancement of the ability of MZF-2A to activate transcription in a luciferase reporter assay. Taken together, these results indicate that MZF-2A is a novel target for the ERK and p38 MAP kinase signaling pathways, and its transactivation activity is negatively regulated by MAP kinase-mediated phosphorylation of the TAD.