title: Biphasic regulation of extracellular signal-regulated kinases by scalaradial, a secretory phospholipase A(2) inhibitor.
abstract: The marine natural product scalaradial (SLD) is a potent inhibitor of secretory phospholipase A(2) (sPLA(2)). Our previous work has demonstrated that SLD inhibits epidermal growth factor receptor-mediated Akt phosphorylation, and this effect is independent of sPLA(2). Here we report the role of SLD in extracellular signal-regulated kinase (ERK)1/2 activation. SLD inhibited ERK1/2 phosphorylation within the first 15 min (early inhibition), then stimulated ERK1/2 phosphorylation after 15 min of SLD treatment (late stimulation) in BEL-7402 cells, displaying biphasic regulatory features. Other PLA(2) inhibitors such as the cytosolic and Ca(2+)-independent PLA(2) inhibitor methyl arachidonyl fluorophosphonate, and another sPLA(2) inhibitor, thioetheramide-phosphatidylcholine, only transiently inhibited ERK1/2 phosphorylation and did not display the stimulatory effect. The early inhibition of ERK1/2 phosphorylation by SLD was reversed by the PLA(2) metabolite arachidonic acid, while the late stimulation was abrogated by constitutively active myristolated-Akt. Furthermore, SLD dose- and time-dependently inhibited the phosphorylation of Raf-1 on Ser 259, which is an established event by which Akt inhibits ERK1/2 activation. Taken together, these data demonstrate a biphasic regulation of ERK1/2 phosphorylation by SLD in a time-dependent manner, i.e., early inhibition and late stimulation. The early inhibition of ERK1/2 phosphorylation is mediated by sPLA(2), at least in part, and the late stimulation is effected through SLD inhibition of Akt. These findings provide further insight into the mechanisms underlying the pharmacological effect of SLD.
authors.affiliation: Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Yili
authors.initials: Y
authors.lastname: Xie
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Yu
authors.forename: Lunhua
authors.initials: L
authors.lastname: Liu
authors.forename: Yuewei
authors.initials: Y
authors.lastname: Guo
authors.forename: Liguang
authors.initials: L
authors.lastname: Lou
mesh_terms: D016718:Arachidonic Acid / Q000494:pharmacology; D001095:Arachidonic Acids / Q000494:pharmacology; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D054501:Group II Phospholipases A2; D006718:Homosteroids / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D008113:Liver Neoplasms / Q000201:enzymology / Q000473:pathology; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D063065:Organophosphonates / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D054830:Sesterterpenes; D015398:Signal Transduction; D013729:Terpenes / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D001095:Arachidonic Acids; D004791:Enzyme Inhibitors; D006718:Homosteroids; D063065:Organophosphonates; D010713:Phosphatidylcholines; D054830:Sesterterpenes; D013729:Terpenes; C104810:methyl arachidonylfluorophosphonate; D016718:Arachidonic Acid; C071197:scalaradial; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D010741:Phospholipases A; D054501:Group II Phospholipases A2