Search

20-Hydroxyeicosatetraenoic acid (20-HETE) has been reported to promote mitogenicity in a variety of cell types, including renal epithelial cells. However, the signal transduction pathways activated by 20-HETE have not been fully defined. The present study evaluated the effects of 20-HETE and its more stable agonist analogs 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid (5,14-20-HEDE) and N-[20-hydroxyeicosa-5(Z),14(Z)-dienoyl]glycine (5,14-20-HEDGE) on the Raf/MEK/ERK and phosphatidylinositol 3-kinase (PI3K)-Akt pathway in LLC-PK~ renal epithelial cells. 20-HETE (20 [micro]M) increased phosphorylation of Raf-1 (2.5 [+ or -] 0.2-fold), MEK 1/2 (6.3 [+ or -] 1.6-fold), and ERKI/2 (5.8 [+ or -] 0.3-fold) compared with vehicle-treated cells. Similarly, the 20-HETE analogs also strongly activated ERK1/2 in a Raf-1- and MEK 1/2-dependent manner. Moreover, 5,14-20-HEDE increased Akt phosphorylation by 2.2 [+ or -] 0.3-fold. 20-HETE and 5,14-20-HEDE also promoted activation (Y1086) of epidermal growth factor receptor (EGFR; Y1086) by 1.9 [+ or -] 0.2- and 2.5 [+ or -] 0.2-fold, respectively. These effects were completely blocked by the EGFR inhibitor EKB-569 (0.1 [micro]M). Moreover, EKB-569 (0.1 [micro]M), as well as a c-Src inhibitor, SKI-606 (0.05 [micro]M), completely abolished the 20-HETE-mediated activation of the Raf/MEK/ERK and PI3K-Akt pathways. Blockade of PKC with bisindolylmaleimide I had no effect on 20-HETE-induced ERK1/2 activation. This study demonstrated that 20-HETE activated the Raf/ MEK/ERK and Akt pathways in renal epithelial cells secondary to the activation of c-Src and EGFR. epithelial cell proliferation; epidermal growth factor receptor; cell signaling

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tibs.2009.02.007 Byline: Linda Vermeulen, Wim Vanden Berghe, Ilse M.E. Beck, Karolien De Bosscher, Guy Haegeman Abstract: Among the mitogen-activated protein kinase (MAPK) targets, MSKs (mitogen- and stress-activated protein kinases) comprise a particularly interesting protein family. Because MSKs can be activated by both extracellular-signal-regulated kinase and p38 MAPKs, they are activated by many physiological and pathological stimuli. About ten years after their original discovery, they have been recognized as versatile kinases regulating gene transcription at multiple levels. MSKs directly target transcription factors, such as cAMP-response-element-binding protein and nuclear factor-[kappa]B, thereby enhancing their transcriptional activity. They also induce histone phosphorylation, which is accompanied by chromatin relaxation and facilitated binding of additional regulatory proteins. Here, we review the current knowledge on MSK activation and its molecular targets, focusing on recent insights into the role of MSKs at multiple levels of transcriptional regulation. Author Affiliation: Laboratory of Eukaryotic Gene Expression & Signal Transduction (LEGEST), Department of Physiology, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium

Research shows that the superantigen gene ypm, encoding Yersinia pseudotuberculosis-derived mitogen, is not associated with mobile genetic elements and inserts into the bacterial genome in an unstable locus on the chromosome. Data indicate that DNA deletion in this locus occurs with high frequency.

The Drosophila p38 MAPK pathway is necessary for egg asymmetric development in oogenesis. The role of p38 MAPK signaling in unchallenged conditions is not well understood. Mutations in a Drosophila p38 MAPKK gene homolog, licorne (lic) has been isolated. It was shown that in oogenesis lic is necessary in the germ line for the asymmetric development of the egg to take place as it should. Loss of lic function in the germ line brings reduced EGF receptor activity in dorsal follicle cells and ventralization of the egg shell. Results of the study constitute the first genetic demonstration of an essential development function of a p38 pathway.

In the yeast Saccharomyces cerevisiae, mating pheromone response is initiated by activation of a G protein- and mitogen-activated protein (MAP) kinase-dependent signaling pathway and attenuated by several mechanisms that promote adaptation or desensitization. To identify genes whose products negatively regulate pheromone signaling, we screened for mutations that suppress the hyperadaptive phenotype of wild-type cells overexpressing signaling-defective G protein [Beta] subunits. This identified recessive mutations in MOT3, which encodes a nuclear protein with two [Cys.sub.2]-[His.sub.2] Zn fingers. MOT3 was found to be a dosage-dependent inhibitor of pheromone response and pheromone-induced gene expression and to require an intact signaling pathway to exert its effects. Several results suggested that Mot3 attenuates expression of pheromone-responsive genes by mechanisms distinct from those used by the negative transcriptional regulators Cdc36, Cdc39, and Mot2. First, a Mot3-lexA fusion functions as a transcriptional activator. Second, Mot3 is a dose-dependent activator of several genes unrelated to pheromone response, including CYC1, SUC2, and LEU2. Third, insertion of consensus Mot3 binding sites (C/A/T)AGG(T/G)A activates a promoter in a MOT3-dependent manner. These findings, and the fact that consensus binding sites are found in the 5[prime] flanking regions of many yeast genes, suggest that Mot3 is a globally acting transcriptional regulator. We hypothesize that Mot3 regulates expression of factors that attenuate signaling by the pheromone response pathway.

Mitogen-activated protein kinase (MAPK) is selectively activated by injecting either mos or MAPK kinase (mek) RNA into immature mouse oocytes maintained in the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). IBMX arrests oocyte maturation, but Mos (or MEK) overexpression overrides this block. Under these conditions, meiosis I is significantly prolonged, and MAPK becomes fully activated in the absence of [p34.sup.cdc2] kinase or maturation-promoting factor. In these oocytes, large openings form in the germinal vesicle adjacent to condensing chromatin, and microtubule arrays, which stain for both MAPK and centrosomal proteins, nucleate from these regions. Maturation-promoting factor activation occurs later, concomitant with germinal vesicle breakdown, the contraction of the microtubule arrays into a precursor of the spindle, and the redistribution of the centrosomal proteins into the newly forming spindle poles. These studies define important new functions for the Mos/MAPK cascade in mouse oocyte maturation and, under these conditions, reveal novel detail of the early stages of oocyte meiosis I.

Platelet-derived growth factors (PDGF) associate with phospholipase C-gamma1 (PLC-gamma1), the Ras GTPase activating protein (RasGAP), phosphatidylinositol 3 kinase (P13K) and a 64-kd protein upon ligand-induced tyrosine phosphorylation. A PDGF receptor mutant which can not bind any factor and mutants which can only bind one of these factors were constructed to determine the role of these factors. Results showed that PLC-gamma1 and P13K are the downstream mediators that initiate DNA synthesis. RasGAP and the 64-kd protein are not sufficient mediators of PDGF's mitogenic signal.

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and key regulator of both physiologic and pathologic (e.g., tumor) angiogenesis. In the course of studies designed to assess the ability of constitutive VEGF to block tumor regression in an inducible RAS melanoma model, mice implanted with VEGF-expressing tumors sustained high morbidity and mortality that were out of proportion to the tumor burden. Documented elevated serum levels of VEGF were associated with a lethal hepatic syndrome characterized by massive sinusoidal dilation and endothelial cell proliferation and apoptosis. Systemic levels of VEGF correlated with the severity of liver pathology and overall clinical compromise. A striking reversal of VEGF-induced liver pathology and prolonged survival were achieved by surgical excision of VEGF-secreting tumor or by systemic administration of a potent VEGF antagonist (VEGF-[TRAP.sub.R1R2]), thus defining a paraneoplastic syndrome caused by excessive VEGF activity. Moreover, this VEGF-induced syndrome resembles peliosis hepatis, a rare human condition that is encountered in the setting of advanced malignancies, high-dose androgen therapy, and Bartonella henselae infection. Thus, our findings in the mouse have suggested an etiologic role for VEGF in this disease and may lead to diagnostic and therapeutic options for this debilitating condition in humans.