Protein phosphatase inhibitors induce the sustained expression of the Egr-1 gene and the hyperphosphorylation of its gene product.
The immediate-early gene Egr-1 is strongly and rapidly induced in human and mouse Balb/c fibroblasts by okadaic acid and calyculin A, both specific inhibitors of protein serine/threonine phosphatases 1 and 2A. In contrast to the transient induction of the Egr-1 gene by serum or phorbol 12-myristate 13-acetate, these phosphatase inhibitors stimulated a sustained induction of the Egr-1 gene. The induction is shown to occur transcriptionally and is sustained post-transcriptionally. Okadaic acid-induced Egr-1 mRNA is significantly more stable than serum-induced Egr-1 mRNA. The half-life of serum-induced Egr-1 mRNA is estimated to be 12 min, compared with a half life of 2 h for okadaic acid-induced Egr-1 mRNA. Okadaic acid also induced the expression of the related immediate-early genes Egr-2 and Egr-3 albeit to a lesser extent than Egr-1. Treatment of cells with okadaic acid and calyculin A also induced the synthesis of Egr-1 protein. The Egr-1 protein is weakly or not phosphorylated in quiescent cells, but multiple species of the phosphorylated forms of the Egr-1 protein are detected in cells treated with either of the phosphatase inhibitors. Simultaneous treatment of cells with TPA and okadaic acid synergistically induced Egr-1 gene expression, and H7 strongly inhibits this induction. Taken together, the results indicate that the induction of Egr-1 gene transcription and the phosphorylation of the induced Egr-1 protein are under the control of protein kinase(s) and protein phosphatase(s). The phosphorylation and dephosphorylation of Egr-1 protein may play a role in controlling cell growth.
Cao
X
X
Signal Transduction Laboratory, National University of Singapore.
Mahendran
R
R
Guy
G R
GR
Tan
Y H
YH
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001769:Blood; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D004247:DNA; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D051766:Early Growth Response Protein 1; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D017874:Immediate-Early Proteins; D007700:Kinetics; D008387:Marine Toxins; D051379:Mice; D008969:Molecular Sequence Data; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D011233:Precipitin Tests; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D004988:Ethers, Cyclic; D017874:Immediate-Early Proteins; D008387:Marine Toxins; D010080:Oxazoles; D014157:Transcription Factors; D019319:Okadaic Acid; C059041:calyculin A; D004247:DNA; D010749:Phosphoprotein Phosphatases