Transient and sustained ERK phosphorylation and nuclear translocation in growth control.
Growth stimulation and inhibition are both associated with tyrosine phosphorylation. We examined the effects of epidermal growth factor (EGF), a growth stimulant, and compound 5 (Cpd 5), a protein-tyrosine phosphatase (PTPase) inhibitor, which inhibits the growth of the same Hep3B hepatoma cells. We found that both EGF and Cpd 5 induced tyrosine phosphorylation of EGF receptor (EGFR) and ERK. However, the phosphorylation caused by EGF was transient and that caused by Cpd 5 was prolonged. Furthermore, Cpd 5 action caused a strong nuclear phospho-ERK signal and induced phospho-Elk-1, a nuclear target of ERK activation, in contrast to the weak effects of EGF. An ERK kinase assay demonstrated that ERK activated by Cpd 5 could phosphorylate its physiological substrate, Elk-1. The MEK inhibitors PD098056 and U0126 abrogated both the induction by Cpd 5 of phospho-ERK, its nuclear translocation and phospho-Elk-1 and also antagonized its growth inhibitory effects. Furthermore, phospho-ERK phosphatase and phospho-Elk-1 activities were lost from nuclear extracts from Cpd 5 treated, but not EGF treated cells. In conclusion, the data show that Cpd 5 causes growth inhibition as a consequence of prolonged ERK and Elk-1 phosphorylation, likely a result of inhibition of multiple PTPases, including those acting on phospho-EGFR, on phospho-ERK, and on phospho-Elk-1, in contrast to the kinase driven transient activation resulting from EGF.
Adachi
Takahito
T
Department of Surgery, Thomas E. Starzl Transplantation Institute, University of Pittsburgh, Pennsylvania 15213, USA.
Kar
Siddhartha
S
Wang
Meifang
M
Carr
Brian I
BI
D021581:Active Transport, Cell Nucleus; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D014812:Vitamin K / Q000031:analogs & derivatives / Q000494:pharmacology*; D050807:ets-Domain Protein Elk-1
C446520:2-(2-hydroxyethylsulfanyl)-3-methyl-1,4-naphthoquinone; D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D004791:Enzyme Inhibitors; D006131:Growth Inhibitors; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D014812:Vitamin K; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D010744:Phosphoric Monoester Hydrolases