Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.11.18 (MAP)
 7,412 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The induction of T-cell growth by the T-cell antigen receptor (TcR) is dependent on a co-ordinated process of phosphorylation and dephosphorylation of intracellular proteins. An intermediary in this signalling pathway is the serine kinase, p42 mitogen-activated protein kinase (p42MAPK), also known as microtubule-associated protein-2 kinase (MAP-2K). MAP-kinase is activated upon the acquisition of tyrosine as well as threonine phosphate groups and removal of either by specific tyrosine or serine/threonine phosphatases abrogates kinase activity. Okadaic acid (OA), a tumour promoter and potent inhibitor of type 1 and 2A serine/threonine protein phosphatases (PP1 and PP2A), induced MAP-kinase activity in Jurkat T cells in a dose-dependent fashion with optimal effect at 1 microM. Compared to rapid activation (peak < 10 min) of MAP-kinase by another tumour promoter, the phorbol ester, PMA, the effect of OA was delayed (> 30 min) and more sustained. In spite of activating a growth-promoting kinase, OA differed from PMA by its lack of mitogenic activity and failure to induce CD25 [interleukin-2R alpha (IL-2R alpha)] expression in normal human T cells. This implies that PP1 and PP2A also act downstream of MAP-kinase to facilitate later cell cycle events. PMA induced a 42,000 MW tyrosine phosphoprotein which co-electrophoresed and co-chromatographed with ERK-2, a p42 MAP-kinase. Although OA induced an identical Mono-Q peak, there was less avid tyrosine phosphorylation of p42. OA also differed from PMA to the extent by which it induced mobility shift of the tyrosine protein kinase, p56lck, which has been implicated in p42MAPK activation in T cells. Taken together, these results indicate that OA and PMA exert both overlapping as well as divergent effects on lymphocyte growth pathways.
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PMID:Contrasting effects of two tumour promoters, phorbol myristate acetate and okadaic acid, on T-cell responses and activation of p42 MAP-kinase/ERK-2. 838 30

The involvement of serine/threonine protein phosphatases in signaling pathways that control the expression of the cyclooxygenase-2 (COX-2) gene in human chondrocytes was examined. Okadaic acid (OKA), an inhibitor of protein phosphatases 1 (PP-1) and 2A (PP-2A), induced a delayed, time-dependent increase in the rate of COX-2 gene transcription (runoff assay) resulting in increased steady-state mRNA levels and enzyme synthesis. The latter response was dose dependent over a narrow range of 1-30 nmol/L with declining expression and synthesis of COX-2 at higher concentrations due to cell toxicity. The delayed increase in COX-2 mRNA expression was accompanied by the induction of the proto-oncogenes c-jun, junB, junD, and c-fos (but not FosB or Fra-1). Increased phosphorylation of CREB-1/ATF-1 transcription factors was observed beginning at 4 h and reached a zenith at 8 h. Gel-shift analysis confirmed the up-regulation of AP-1 and CRE nuclear binding proteins, though there was little or no OKA-induced nuclear protein binding to SP-1, AP-2, NF-kappaB or NF-IL-6 regulatory elements. OKA-induced nuclear protein binding to 32P-CRE oligonucleotides was abrogated by a pharmacological inhibitor of protein kinase A (PKA), KT-5720; the latter compound also inhibited OKA-induced COX-2 enzyme synthesis. Calphostin C (CalC), an inhibitor of PKC isoenzymes, had little effect in this regard. Inhibition of 12P-CRE binding was also observed in the presence of an antibody to CREB-binding protein (265-kDa CBP), an integrator and coactivator of cAMP-responsive genes. The binding to 32P-CRE was unaffected in the presence of excess radioinert AP-1 and COX-2 NF-IL-6 oligonucleotides, although a COX-2 CRE-oligo competed very efficiently. 32P-AP-1 consensus sequence binding was unaffected by incubation of chondrocytes with KT-5720 or CalC, but was dramatically diminished by excess radioinert AP-1 and CRE-COX-2 oligos. Supershift analysis in the presence of antibodies to c-Jun, c-Fos, JunD, and JunB suggested that AP-1 complexes were composed of c-Fos, JunB, and possibly c-Jun. OKA has no effect on total cellular PKC activity but caused a delayed time-dependent increase in total PKA activity and synthesis. OKA suppressed the activity of the MAP kinases, ERK1/2 in a time-dependent fashion, suggesting that the Raf-1/MEKK1/MEK1/ERK1,2 cascade was compromised by OKA treatment. By contrast, OKA caused a dramatic increase in SAPK/JNK expression and activity, indicative of an activation of MEKK1/JNKK/SAPK/JNK pathway. OKA stimulated a dose-dependent activation of CAT activity using transfected promoter-CAT constructs harboring the regulatory elements AP-1 (c-jun promoter) and CRE (CRE-tkCAT). We conclude that in primary phenotypically stable human chondrocytes, COX-2 gene expression may be controlled by critical phosphatases that interact with phosphorylation dependent (e.g., MAP kinases:AP-1, PKA:CREB/ATF) signaling pathways. AP-1 and CREB/ATF families of transcription factors may be important substrates for PP-1/PP-2A in human chondrocytes.
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PMID:Transcriptional induction of cyclooxygenase-2 gene by okadaic acid inhibition of phosphatase activity in human chondrocytes: co-stimulation of AP-1 and CRE nuclear binding proteins. 962 Jan 67

Okadaic acid (OA) is the major component of diarrhetic shell fish poisoning toxins and a potent inhibitor of protein phosphatase 1 and 2A. We investigated the signal transduction pathways involved in OA induced cell death in HeLa cells. OA induced cytotoxicity and apoptosis at IC50 of 100nM. OA treatment resulted in time dependent increase in reactive oxygen species and depleted intracellular glutathione levels. Loss of mitochondrial membrane permeability led to translocation of bax, cytochrome-c and AIF from mitochondria to cytosol. The cells under fluorescence microscope showed typical apoptotic morphology with condensed chromatin, and nuclear fragmentation. We investigated the mitochondrial-mediated caspase cascade. The time dependent activation and cleavage of of bax, caspases-8, 10, 9, 3 and 7 was observed in Western blot analysis. In addition to caspase-dependent pathway AIF mediated caspase-independent pathway was involved in OA mediated cell death. OA also caused time dependent inhibition of protein phosphatase 2A activity and phosphorylation of p38 and p42/44 MAP kinases. Inhibitor studies with Ac-DEVO-CHO and Z-VAD-FMK could not prevent the phosphorylation of p38 and p42/44 MAP kinases. Our experiments with caspase inhibitors Ac-DEVD-CHO, Z-IETD-FMK and Z-VAD-FMK inhibited capsase-3, 8 cleavages but did not prevent OA-induced apoptosis and DNA fragmentation. Similarly, pretreatment with cyclosporin-A and N-acetylcysteine could not prevent the DNA fragmentation. In summary, the results of our study show that OA induces multiple signal transduction pathways acting either independently or simultaneously leading to apoptosis.
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PMID:Multiple signal transduction pathways in okadaic acid induced apoptosis in HeLa cells. 1908 44

Okadaic acid (OKA) and analogues are frequent contaminants of coastal waters and seafood. Structure analysis of the isolated OKA analogue 19-epi-OKA showed important conformation differences expected to result in lower protein phosphatase (PP) inhibitory potencies than OKA. However, 19-epi-OKA and OKA inhibitory activities versus PP2A were unexpectedly found to be virtually equipotent. To investigate the toxicological relevance of these findings, we tested the effects of 19-epi-OKA on cultured cerebellar cells and compared them with those of OKA and its isomer dinophysistoxin-2. 19-epi-OKA caused degeneration of neurites and neuronal death with much lower potency than its congeners. The concentration of 19-epi-OKA that reduced after 24h the maximum neuronal survival (EC5024) by 50% was ~300nM compared with ~2nM and ~8nM for OKA and dinophysistoxin-2, respectively. Exposure to 19-epi-OKA resulted also in less toxicity for cultured glial cells (EC5024,19-epi-OKA ~ 600nM; EC5024,OKA ~ 20nM). 19-epi-OKA induced apoptotic condensation and fragmentation of chromatin, activation of caspases, and activation of ERK1/2 MAP kinases, features previously reported for OKA and dinophysistoxin-2. Also, differential sensitivity to 19-epi-OKA was observed between neuronal and glial cells, a specific characteristic shared by OKA and dinophysistoxin-2 but not by other toxins. Our results are consistent with 19-epi-OKA being included among the group of toxins of OKA and derivatives and support the suitability of cellular bioassays for the detection of these compounds.
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PMID:Comparative toxicological study of the novel protein phosphatase inhibitor 19-Epi-okadaic acid in primary cultures of rat cerebellar cells. 2333 26