Tumor necrosis factor α: Posttranscriptional stabilization of WAF1 mRNA in p53-deficient human leukemic cells

Abstract

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.

Redox‐Mediated Regulation of p21Waf1/Cip1 Expression Involves a Post‐Transcriptional Mechanism and Activation of the Mitogen‐Activated Protein Kinase Pathway

“…Thus, even a modest increase in mRNA stability would result in the rapid accumulation of p21waf1/c1~t mRNA. Our findings are consistent with recent reports of an increase in the half-life of p2Iwt1/"p' mRNA in human KG-1 myeloblastic cells after exposure to tumor necrosis factor-a [36], in normal human fibroblasts (Wl38) after exposure to interleukin-I [37] and in HL-60 cells after treatment with TPA or dihydroxyvitamin D, [ 111. Nevertheless, transcriptional activation may contribute to the p53-independent induction of The physiological role of the MAPK-dependent, p53-independent pathway of p2lWaf1/"p1 mRNA induction is unknown.…”

Resistance of MCF7 human breast carcinoma cells to TNF-induced cell death is associated with loss of p53 function

“…However it should be noted that in some p53 de®cient myeloid leukemic cell lines (K562, HL60), TNF was e cient to induce a cytostatic e ect (Shiohara et al, 1996). This further con®rms that TNF has strikingly di erent e ects according to the cell type.…”

The ability to cleave 28S ribosomal RNA during apoptosis is a cell-type dependent trait unrelated to DNA fragmentation

“…The reason for including three p53-negative cell lines (HL-60, U937 and K562) (Shiohara et al, 1996) was a reported covalent association between 5.8S rRNA and a C-terminal serine-residue in p53 (Samad and Carroll, 1991;Fontoura et al, 1992). Because (wild-type) p53 expression can induce apoptosis, it was of interest to determine if apoptotic 28S rRNA fragmentation correlated with this p53/rRNA association.…”