title: EGFR-independent activation of ERK1/2 mediates growth inhibition by a PTPase antagonizing K-vitamin analog.
abstract: The K-vitamin analog Cpd 5 or [2-(2-mercaptoethanol)-3-methyl-1,4-napthoquinone] is a potent cell growth inhibitor in vitro and in vivo, likely due to arylation of enzymes containing a catalytic cysteine. This results in inhibition of protein tyrosine phosphatase (PTPase) activity with resultant hyperphosphorylation of EGF receptors (EGFR) and ERK1/2 protein kinases, which are downstream to EGFR in the MAPK pathway. We used NR6 fibroblast cells, which lack endogenous EGFR and its variant cells transfected with different EGFR mutants to assess the contribution of the EGFR-mediated signaling pathway to Cpd 5-mediated ERK activation and cell growth inhibition. Cpd 5 treatment resulted in enhanced phosphorylation of EGFR at carboxyl-terminal tyrosines. This phosphorylation and activation of EGFR were found to be necessary neither for growth inhibition nor for the activation of the downstream kinases ERK1/2, since both occurred in EGFR-devoid mutant cells. U0126 and PD 098059, specific inhibitors of MEK1/2, the ERK1/2 kinases, antagonized both cell growth inhibition and ERK1/2 phosphorylation mediated by Cpd5. Cpd 5 was also found to inhibit ERK1/2 phosphatase(s) activity in lysates from all the cells tested, irrespective of their EGFR status. These results show that EGFR-independent ERK1/2 phosphorylation was involved in the mechanism of Cpd5 mediated growth inhibition. This is likely due to the observed antagonism of ERK phosphatase activity. A candidate PTPase was found to be Cdc25A, a recently identified ERK phosphatase.
authors.affiliation: Starzl Transplantation Institute, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Kar
authors.forename: Takahito
authors.initials: T
authors.lastname: Adachi
authors.forename: Brian I
authors.initials: BI
authors.lastname: Carr
mesh_terms: D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism*; D006131:Growth Inhibitors / Q000494:pharmacology*; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation / Q000502:physiology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D012016:Reference Values; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000494:pharmacology*; D020687:cdc25 Phosphatases / Q000378:metabolism
chemical_list: C446520:2-(2-hydroxyethylsulfanyl)-3-methyl-1,4-naphthoquinone; D006131:Growth Inhibitors; D014812:Vitamin K; D014443:Tyrosine; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010744:Phosphoric Monoester Hydrolases; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases