Tumor necrosis factor alpha: posttranscriptional stabilization of WAF1 mRNA in p53-deficient human leukemic cells.
The p53 protein directly regulates the expression of the WAF1 (wild-type p53-activated fragment 1) protein which is a cyclin-dependent kinase inhibitor (CDK1). DNA damaging agents such as ionizing or UV radiation, and some chemical agents induce WAF1 in wild-type p53 containing cells, thereby halting cell cycle progression. WAF1 expression is also induced through a p53-independent pathway. Tumor necrosis factor alpha (TNF alpha) is a cytotoxic/cytostatic compound for some human cancer cells. We examined a series of myeloid leukemic cell lines that expressed either no p53 (HL-60, K562) or mutant inactive p53 (KG-1, KCL22,THP-1, U937). The KG-1, HL-60, K562, and KCL22 myeloid leukemic cells increased their levels of WAF1 mRNA in the presence of TNF alpha. We focused on KG-1 cells to determine how TNF alpha modulated WAF1 expression. WAF1 mRNA increased in a dose-dependent manner in the cells after exposure to increasing concentrations of TNF alpha, and this increase occurred in the absence of new protein synthesis. An increase of WAF1 protein and a concominant decrease of cyclin-dependent kinase 2 activity also was found in KG-1 cells. Flow cytometry using 5-bromo-2'-deoxyuridine showed an increase in the proportion of TNF alpha- treated KG-1 cells in the G0/G1 phase of the cell cycle. TNF alpha enhanced the rate of WAF1 transcription only 1.4 fold in TNF alpha-treated KG-1 cells as compared to untreated cells. Notably, however, the half-life (t 1/2) of WAF1 mRNA in TNF alpha-treated cells was 2.5 hours as compared to 0.5 hours in untreated cells. These results indicate that TNF alpha increases WAF1 levels at least in part via a postttranscriptional stabilization of the mRNA; and TNF alpha may mediate its cytostatic effects through WAF1 in some cell types.
Shiohara
M
M
Department of Medicine, Division of Hematology/Oncology, UCLA School of Medicine, Cedars-Sinai Research Institute, Los Angeles, CA 90048, USA.
Akashi
M
M
Gombart
A F
AF
Yang
R
R
Koeffler
H P
HP
D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics*; D003513:Cycloheximide / Q000494:pharmacology; D004791:Enzyme Inhibitors; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007951:Leukemia, Myeloid; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000096:biosynthesis / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D003513:Cycloheximide; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases