title: Cdc25A and ERK interaction: EGFR-independent ERK activation by a protein phosphatase Cdc25A inhibitor, compound 5.
abstract: Extracellular signal-regulated kinase (ERK) plays a central role in regulating cell growth, differentiation, and apoptosis. We previously found that 2-(2-mercaptoethanol)-3-methyl-1,4-napthoquinone or Compound 5 (Cpd 5), is a Cdc25A protein phosphatase inhibitor and causes prolonged, strong ERK phosphorylation which is triggered by epidermal growth factor receptor (EGFR) activation. We now report that Cpd 5 can directly cause ERK phosphorylation by inhibiting Cdc25A activity independently of the EGFR pathway. We found that Cdc25A physically interacted with and de-phosphorylated phospho-ERK both in vitro and in cell culture. Inhibition of Cdc25A activity by Cpd 5 resulted in ERK hyper-phosphorylation. Transfection of Hep3B human hepatoma cells with inactive Cdc25A mutant enhanced Cpd 5 action on ERK phosphorylation, whereas over-expression of Cdc25A attenuated this Cpd 5 action. Furthermore, endogenous Cdc25A knock-down by Cdc25A siRNA resulted in a constitutive-like ERK phosphorylation and Cpd 5 treatment further enhanced it. In EGFR-devoid NR6 fibroblasts and MEK (ERK kinase) mutated MCF7 cells, Cpd 5 treatment also resulted in ERK phosphorylation, providing support for the idea that Cpd 5 can directly act on ERK phosphorylation by inhibiting Cdc25A activity. These data suggest that phospho-ERK is likely another Cdc25A substrate, and Cpd 5-caused ERK phosphorylation is probably regulated by both EGFR-dependent and EGFR-independent pathways.
authors.affiliation: Thomas E. Starzl Transplant Institute, Department of Surgery, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Ziqiu
authors.initials: Z
authors.lastname: Wang
authors.forename: Baochun
authors.initials: B
authors.lastname: Zhang
authors.forename: Meifang
authors.initials: M
authors.lastname: Wang
authors.forename: Brian I
authors.initials: BI
authors.lastname: Carr
mesh_terms: D045744:Cell Line, Tumor; D002474:Cell-Free System; D018076:DNA, Complementary / Q000494:pharmacology; D004347:Drug Interactions; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D008623:Mercaptoethanol / Q000031:analogs & derivatives* / Q000494:pharmacology; D009285:Naphthoquinones / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D014162:Transfection; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism*
chemical_list: C111898:2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D009285:Naphthoquinones; D034741:RNA, Small Interfering; D008623:Mercaptoethanol; D066246:ErbB Receptors; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases