Activation of early growth response 1 gene transcription and pp90rsk during induction of monocytic differentiation.
The present work has studied mechanisms responsible for induction of early growth response 1 (EGR-1) gene expression during monocytic differentiation of U-937 myeloid leukemia cells. Differentiation of U-937 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of the serine/threonine protein kinase C, was associated with transcriptional activation of EGR-1 promoter-reporter constructs. The EGR-1 promoter contains six CC(A/T)6GG (CArG) motifs. The two 5'-most distal CArG sequences conferred TPA inducibility. In contrast, there was little effect of TPA on EGR-1 transcription in a TPA-resistant U-937 cell variant, designated TUR. Treatment of both U-937 and TUR cells with okadaic acid, an inhibitor of serine/threonine protein phosphatases 1 and 2A, was associated with induction of monocytic differentiation and EGR-1 transcription through the 5'-most CArG element. Since these findings supported the involvement of serine/threonine protein phosphorylation in the regulation of EGR-1 expression, we studied activation of the 40S ribosomal protein S6 serine/threonine kinases, pp70S6K and pp90rsk. Although both kinases participate in regulating cell growth, there was no detectable activation of pp70S6K during TPA- or okadaic acid-induced monocytic differentiation. Moreover, rapamycin, an inhibitor of pp70S6K activation, had no effect on induction of EGR-1 expression. In contrast, analysis of pp90rsk activity by phosphorylation of a peptide derived from S6 protein demonstrated stimulation of this kinase in TPA-treated U-937, and not TUR, cells. Okadaic acid treatment of both cell types was associated with activation of pp90rsk.(ABSTRACT TRUNCATED AT 250 WORDS)
Kharbanda
S
S
Division of Cancer Pharmacology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
Saleem
A
A
Hirano
M
M
Emoto
Y
Y
Sukhatme
V
V
Blenis
J
J
Kufe
D
D
D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D051766:Early Growth Response Protein 1; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017874:Immediate-Early Proteins; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D019319:Okadaic Acid; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000502:physiology*; D019893:Ribosomal Protein S6 Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D004988:Ethers, Cyclic; D017874:Immediate-Early Proteins; D014157:Transcription Factors; D019319:Okadaic Acid; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D013755:Tetradecanoylphorbol Acetate