Polyamine depletion stabilizes p53 resulting in inhibition of normal intestinal epithelial cell proliferation

Abstract

The p53 nuclear phosphoprotein plays a critical role in transcriptional regulation of target genes involved in growth arrest and apoptosis. The natural polyamines, including spermidine, spermine, and their precursor putrescine, are required for cell proliferation, and decreasing cellular polyamines inhibits growth of the small intestinal mucosa. In the current study, we investigated the mechanisms of regulation of p53 gene expression by cellular polyamines and further determined the role of the gene product in the process of growth inhibition after polyamine depletion. Studies were conducted both in vivo and in vitro using rats and the IEC-6 cell line, derived from rat small intestinal crypt cells. Levels for p53 mRNA and protein, transcription and posttranscription of the p53 gene, and cell growth were examined. Depletion of cellular polyamines by treatment with alpha-difluoromethylornithine (DFMO) increased p53 gene expression and caused growth inhibition in the intact small intestinal mucosa and the cultured cells. Polyamine depletion dramatically increased the stability of p53 mRNA as measured by the mRNA half-life but had no effect on p53 gene transcription in IEC-6 cells. Induction of p53 mRNA levels in DFMO-treated cells was paralleled by an increase in the rate of newly synthesized p53 protein. The stability of p53 protein was also increased after polyamine depletion, which was associated with a decrease in Mdm2 expression. When polyamine-deficient cells were exposed to exogenous spermidine, a decrease in p53 gene expression preceded an increase in cellular DNA synthesis. Inhibition of the p53 gene expression by using p53 antisense oligodeoxyribonucleotides significantly promoted cell growth in the presence of DFMO. These findings indicate that polyamines downregulate p53 gene expression posttranscriptionally and that growth inhibition of small intestinal mucosa after polyamine depletion is mediated, at least partially, through the activation of p53 gene.

Nuclear Magnetic Resonance Spectroscopy-Based Metabolite Profiling of Transgenic Tomato Fruit Engineered to Accumulate Spermidine and Spermine Reveals Enhanced Anabolic and Nitrogen-Carbon Interactions

“…Data are represented as means 6 SEM; n 5 8. between different coactivators without altering the state of the chromatin (Maeda et al, 2002) or by affecting histone acetylation/deacetylation (Hobbs and Gilmour, 2000). Also, a posttranscriptional role for polyamines has been shown in down-regulating animal genes (Li et al, 2001), while a certain group of Escherichia coli genes is controlled by the diamine putrescine at the translational level (Yoshida et al, 2004). In the latter case, it was suggested that putrescine enhances transcription of a group of genes by increasing the level of transcription factors.…”

Polyamines as anabolic growth regulators revealed by transcriptome analysis and metabolite profiles of tomato fruits engineered to accumulate spermidine and spermine

“…In animal cells, higher PAs regulate transcription by acting as a switch between different coactivators without altering the state of the chromatin (Maeda et al 2002) or by affecting histone acetylation/deacetylation (Hobbs and Gilmour 2000). Also, a posttranscriptional role for PAs has been shown in down-regulating animal genes (Li et al 2001) while a certain group of Escherichia coli genes is controlled by the diamine putrescine at the translational level (Yoshida et al 2004). In the latter case, it was suggested that putrescine enhances transcription of a group of genes by increasing the level of transcription factors.…”

Protective Role of Arginase in a Mouse Model of Colitis

“…Because NO can inhibit ODC by S-nitrosylation (34), this could interfere with colonic ODC activity. Polyamines have been shown to have numerous biological functions that may be relevant to amelioration of colitis, including inhibition of monocyte activation and Th1 cytokine production (35), stimulation of epithelial restitution by enhancing cell migration (36) and proliferation (37), and regulation of apoptosis (38). It has been demonstrated that polyamine production is essential for the repair of rat duodenal mucosa after stress (39), and that ODC activity is increased in the acetic acid colitis model (40).…”