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      Euphorbias of South Africa: Two new phorbol esters from Euphorbia bothae

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          Abstract

          Two known phorbol esters, 12-deoxyphorbol-13-isobutyrate-20-acetate (1) and 12-deoxyphorbol-13-(2-methylbutyrate)-20-acetate (2), and two new phorbol esters, 12-deoxyphorbol-13-isobutyrate-16-angelate-20-acetate (3) and 12-deoxyphorbol-13-(2-methylbutyrate)-16-angelate-20-acetate (4), were isolated from the endemic South African plant Euphorbia bothae. Standard spectroscopic techniques were used to elucidate the structures of all four compounds. The interaction of 1-4 with opioid receptors was explored in an attempt to explain the unexplained stupor occasionally observed in herbivores browsing on E. bothae.

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          Structural biology of NCAM homophilic binding and activation of FGFR.

          Vladimir Berezin, Vladislav Soroka, Vladislav Kiselyov … (2005)
          In this review, we analyse the structural basis of the homophilic interactions of the neural cell adhesion molecule (NCAM) and the NCAM-mediated activation of the fibroblast growth factor receptor (FGFR). Recent structural evidence suggests that NCAM molecules form cis-dimers in the cell membrane through a high affinity interaction. These cis-dimers, in turn, mediate low affinity trans-interactions between cells via formation of either one- or two-dimensional 'zippers'. We provide evidence that FGFR is probably activated by NCAM very differently from the way by which it is activated by FGFs, reflecting the different conditions for NCAM-FGFR and FGF-FGFR interactions. The affinity of FGF for FGFR is approximately 10(6) times higher than that of NCAM for FGFR. Moreover, in the brain NCAM is constantly present on the cell surface in a concentration of about 50 microm, whereas FGFs only appear transiently in the extracellular environment and in concentrations in the nanomolar range. We discuss the structural basis for the regulation of NCAM-FGFR interactions by two molecular 'switches', polysialic acid (PSA) and adenosine triphosphate (ATP), which determine whether NCAM acts as a signalling or an adhesion molecule.
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            Induction of an immediate early gene egr-1 by zinc through extracellular signal-regulated kinase activation in cortical culture: its role in zinc-induced neuronal death.

            Timothy J. Koh, J. Park, B. Venton (1999)
            Egr-1 is one of the immediate early transcription factors that are induced after brain insults. However, the mechanism and the role of Egr-1 induction are not yet determined. In the present study, using mouse cortical cultures, we examined the ionic mechanism of Egr-1 induction and its role in neuronal death. Although zinc, NMDA, or ionomycin induced comparable neuronal death in cortical culture, only zinc increased Egr-1 expression, which was attenuated by blocking zinc influx. It is intriguing that brief exposure to zinc induced sustained extracellular signal-regulated kinase (Erk) activation. PD098059, an inhibitor of the Erk 1/2 upstream kinase mitogen-activated protein kinase kinase 1 (MEK1), blocked Erk 1/2 activation, Egr-1 induction, and neuronal death by zinc. The present study has demonstrated that zinc, rather than calcium, induces lasting Egr-1 expression in cortical culture by activating Erk 1/2, which is part of a cascade that may play an active role in zinc neurotoxicity. We propose that translocation of endogenous zinc may be the key mechanism of Egr-1 induction and neuronal death in brain ischemia.
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              The production of arachidonic acid can account for calcium channel activation in the second messenger pathway underlying neurite outgrowth stimulated by NCAM, N-cadherin, and L1.

              Nathalie E. Williams, Judy P. Doherty, Michael F. Walsh (1994)
              We have used monolayers of control 3T3 fibroblasts and 3T3 fibroblasts expressing transfected cell adhesion molecules (CAMs)--NCAM, N-cadherin, and L1--as a culture substrate for cerebellar neurones. The transfected CAMs promote neurite outgrowth by activating a second messenger pathway that culminates in calcium influx into neurones through N- and L-type calcium channels. We show that the same neurite outgrowth response can be directly induced by arachidonic acid (10 microM) and that this response can be inhibited by N- and L-type calcium channel antagonists. In cells, arachidonic acid can be generated by phospholipase A2 or by the sequential activities of a phospholipase C (to generate diacylglycerol) and diacylglycerol lipase. In the present study we show the neurite outgrowth stimulated by CAMs (but not by various other agents) can be abolished by an inhibitor of diacylglycerol lipase acting at a site upstream from calcium channel activation. The results suggest that arachidonic acid and/or one of its metabolites is the second messenger that activates calcium channels in the CAM signalling pathway leading to axonal growth, and this is supported by recent evidence that shows the same concentrations of arachidonic acid can increase voltage-dependent calcium currents in cardiac myocytes.
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                Author and article information

                Contributors
                Wendy L. Popplewell: Role: ND
                Eloise A. Marais: Role: ND
                Linda Brand: Role: ND
                Brian H. Harvey: Role: ND
                Michael T. Davies-Coleman: Role: ND
                Journal
                Journal ID (publisher): sajc
                Title: South African Journal of Chemistry
                Abbreviated Title: S.Afr.j.chem. (Online)
                Publisher: The South African Chemical Institute (Durban )
                ISSN: 1996-840X
                Publication date (Print): 2010
                Volume: 63
                Issue: 0
                Pages: 175-179
                Affiliations
                [1 ] Rhodes University South Africa
                [2 ] North-West University South Africa
                Article
                Publisher ID: S0379-43502010000100027
                SO-VID: 66ae1b39-7a82-4984-b0c2-f9501041c9fd
                License:

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO South Africa

                Self URI (journal page): http://www.scielo.org.za/scielo.php?script=sci_serial&pid=0379-4350&lng=en
                Categories
                Subject: Chemistry, Analytical
                Subject: Chemistry, Applied
                Subject: Chemistry, Inorganic & Nuclear
                Subject: Chemistry, Medicinal
                Subject: Chemistry, Multidisciplinary
                Subject: Chemistry, Organic
                Subject: Chemistry, Physical
                Subject: Electrochemistry

                ScienceOpen disciplines: Electrochemistry,Clinical chemistry,Organic & Biomolecular chemistry,Physical chemistry,Analytical chemistry,General chemistry,Industrial chemistry,Inorganic & Bioinorganic chemistry
                Keywords: Euphorbia bothae,Euphorbiaceae,phorbol ester,opioid receptor
                Data availability:
                ScienceOpen disciplines: Electrochemistry, Clinical chemistry, Organic & Biomolecular chemistry, Physical chemistry, Analytical chemistry, General chemistry, Industrial chemistry, Inorganic & Bioinorganic chemistry
                Keywords: Euphorbia bothae, Euphorbiaceae, phorbol ester, opioid receptor

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