Aberrant methylation of c-myc and c-fos protooncogenes and p53 tumor suppressor gene in myelodysplastic syndromes and acute non-lymphocytic leukemia.

PURPOSE: Aberrant methylation, as an epigenetic phenomenon, may precede and regulate the expression of genes involved in transformation mechanisms that lead to leukemogenesis of hemopoietic cells. The genes involved mostly encode transcription factors and cell cycle specific inhibitors. The aim of this project was to study the DNA methylation pattern of c-myc, c-fos and p53 in myelodysplastic syndromes (MDS) and in acute non-lymphocytic leukemias (ANLL). PATIENTS AND METHODS: DNA was isolated from the monocyte cell layer harvested from bone marrow or peripheral blood samples of 44 patients suffering from MDS and ANLL. Genomic DNA was digested with methylation-specific enzymes, and was electrophoresed and hybridized with probes specific for human c-myc, c-fos and p53 genes. RESULTS: In MDS, the c-myc gene in exons 2 and 3 was regionally hypomethylated, whereas exon 2 in ANLL was hypermethylated and exon 3 hypomethylated. The c-fos gene was hypomethylated in ANLL type 4 and presented aberrant hypomethylation in the different types of MDS. The p53 anti-oncogene appeared extensively hypomethylated in MDS. CONCLUSION: Aberrant DNA methylation pattern of the c-myc, c-fos and p53 tumor suppressor gene seems to be a primary event in the transformation process from myelodysplasia to acute leukemia, affecting their expression, and, consequently, altering the proliferation, differentiation or apoptosis of hemopoietic precursor cells. The p53 hypomethylation predisposes to critical mutations that enhance the transformation process of myelodysplasia to leukemia. The recognition of altered methylation of these genes in myelodysplasia may have prognostic implications and may lead to novel therapeutic modalities.

Growth hormone and insulin-like growth factor I protect intestinal cells from radiation induced apoptosis.

We studied whether programmed cell death (or apoptosis) is the predominant mechanism in radiation-induced cell damage to rat intestinal mucosa and investigated the mechanism of the protective effect of GH and IGF-I in the same model. Male albino Wistar rats were divided into four groups: controls, radiation, radiation plus GH and radiation plus IGF-I. Radiation was administered on the first day and on day 4. All animals were sacrificed and segments of the terminal ileum were stained with hematoxylin-eosin. Apoptosis of the epithelial cells was identified at the cellular level by the TUNEL stain and was distinguished from necrosis by the characteristic morphology of the cells (cytoplasmic shrinkage, marginal chromatin condensation and generation of nuclear apoptotic bodies). Apoptotic cells in the control animals were few and detected only at the tips of the villi while in the irradiated animals almost all the epithelial cells were apoptotic, distributed from the crypts to the tips of the villi and the mucosa showed severe epithelial atrophy and ulceration. The histologic picture of the mucosa in the GH and IGF-I treated animals was similar to normal controls and apoptotic cells were restricted only at the tips of the villi. DNA and RNA from the mucosa cells were isolated and analyzed by electrophoresis. DNA fragmentation and RNA 28s band ribonuclease cleavage was observed only in the irradiated animals. We have shown that abdominal radiation causes intestinal epithelial cell damage mainly through the induction of apoptosis and the treatment with GH and IGF-I inhibits apoptosis of the cells and preserves the mucosal integrity.

Relationship between c-src tyrosine kinase activity and the control of glucose transporter gene expression.

It has been shown previously that the rate of glucose transport in fibroblasts is accelerated by oncoproteins such as v-src, ras, and the transforming protein of feline sarcoma virus. This induction of glucose transport is associated with, and presumably caused by, induction of Hep-G2/rat brain glucose transporter gene expression. To determine the mechanism underlying the induction of glucose transporter gene expression by the v-src oncogene we studied cell lines that overexpress the normal counterpart of the v-src protein (c-src), or various mutants of the c-src protein. In these mutants, the tyrosines at positions 416, 527, or 519, or various combinations of these, have been replaced by phenylalanine by site directed mutagenesis, resulting in mutated c-src proteins that possess varying tyrosine kinase activity and transforming potential. Cells that overexpress the c-src protein show no changes in glucose transporter gene expression. However, when Tyr 527 in the COOH terminus of the c-src protein is replaced with Phe, the tyrosine kinase activity and transforming potential of the protein are increased and the protein acquires a potent ability to increase levels of glucose transporter mRNA and protein, as well as the rate of 2-deoxy-D-glucose uptake. This ability is abolished by the double mutation of Tyr to Phe in positions 416 and 527, which reduces the tyrosine kinase activity of the 527 single mutant. Thus, the ability of src proteins to induce expression of the glucose transport system is linked to the tyrosine kinase activity of the protein.(ABSTRACT TRUNCATED AT 250 WORDS)