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The TP53 tumor suppressor gene plays important roles in genomic stability. A common polymorphism at codon 72 of TP53 gene has been associated with increased risk for many human cancers. The p53 protein is expressed in colorectal cancer, but the reported prevalence of its expression varies widely. In the present study, the p53 protein expression in different genotypes of its codon 72, was investigated. We undertook a case-control study on 250 controls and 250 paraffin block specimens of sporadic colorectal adenocarcinomas from the city of Isfahan. PCR amplification of TP53 codon 72 polymorphism: TP53 codon 72 genotypes were detected by PCR using specific primer pairs for amplifying the proline or the arginine Alleles. The PCR reaction was done separately for each of the two polymorphic variants. The amplified products were subjected to electrophoresis on 1% agarose gel in 1× TBE buffer and visualized on a transilluminator using ethidium bromide. Immunohistochemical Staining: We evaluated the expression patterns of p53 protein, as potential prognostic marker in colorectal cancer specimens by immunohistochemical staining. Statistical analyses: The χ2-test was used to assess the significance of any difference in the prevalence of TP53 codon 72 polymorphism between colorectal cancer patients and controls. The odds ratio and 95% CI (confidence intervals) was used as a measure of the strength of the association. Statistical significance level was set to P≤0.05. In control samples, the genotype distribution for TP53 polymorphism showed 30.4%, 45.2% and 24.4% for the arginine/arginine, arginine/proline and proline/proline genotypes, respectively. Allelic frequencies corresponded to 0.663 for the arginine allele and 0.338 for the proline allele. In the cancer group 38.8% of the cases were arginine/arginine, 40.4% were arginine/proline and 20.8% were proline/proline. The corresponding frequencies were 0.590 for the arginine allele and 0.410 for the proline allele. A significant difference between cases and controls was found for the arginine/arginine genotype compared with (grouped) arginine/proline and proline/proline genotypes (Odds Ratio = 1.451 (1.002-2.103), P=0.048). Overexpression of p53 was observed in 50.8 percent of cancer specimens which most of them were arginine/arginine genotype (P<0.001). TP53 polymorphism and arginine/arginine genotype may be correlated with overexpression of p53 and increased risk for colorectal cancer in city of Isfahan.

The polymorphic variants at codon 72 of the p53 gene, encoding proline or arginine at residue 72, produce marked changes in the p53 structure. From the evidence that the DNA mismatch repair system and p53 interact to maintain genomic integrity, we hypothesized that codon 72 variations may influence the prevalence of microsatellite instability (MSI), a feature of malignancies associated with mismatch repair deficiency in sporadic colorectal cancer. We investigated the frequency of MSI in three P53 codon 72 genotypes using genomic DNAs from 144 paraffin blocks of sporadic colorectal adenocarcinomas by testing the BAT-26 poly(A) marker. We used PCR-SSCP analysis to detect tumor sample MSI for the nonisotopic detection of deletions in the BAT- 26 poly (A) mononucleotide repeat. Associations between qualitative variables were evaluated using the χ2-test. Statistical significance level was set to p ≤ 0.05. MSI analysis revealed that 24.3% of the tumors (n=35) were MSI-positive and 75.7% (n=109) were MSI-negative. The frequency of microsatellite instability in the arginine/arginine, arginine/proline and proline/proline genotypes were 11 (16.9%), 22 (36.1%) and 2 (11.1%) respectively. A significant difference in distribution of MSI was found for the arginine/proline genotype compared with the grouped arginine/arginine and proline/proline genotypes (p=0.05). Our findings suggested that colorectal adenocarcinomas arising in individuals with the p53 codon 72 arginine/proline heterozygosity are more prone to microsatellite instability than those with other p53 genotypes. In our study, MSI was important in the carcinogenesis of sporadic colorectal cancer arising in pro/arg heterozygotes.

The polymorphic variants at codon 72 of the p53 gene، encoding either proline or arginine at residue 72، produce marked change in the structure of p53. From the evidence that the DNAmismatch repair system and p53 interact to maintain genomic integrity، we hypothesized that the codon 72 variation may influence the prevalence of microsatellite instability; a feature of malignancies associated with mismatch repair deficiency in breast invasive ductal carcinoma. TP53 codon 72 genotypes were detected by PCR using specific primer pairs for amplifying the Proline or the Arginine Alleles. Then، the frequencies of microsatellite instability (MSI) were analyzed in three genotypes of P53 codon 72 using genomic DNAs from 120 specimens of breast ductal carcinomas by testing the BAT-26 marker. From 120 specimens، 73 (60. 8%) was Arg/Arg، 31 (25. 8%) Arg/Pro and 16 (13. 3%) Pro/Pro. MSI analysis revealed that 24. 2% of the tumors (29 patients) was microsatellite instability-positive and 75. 8% (91 patients) was microsatellite instability -negative. The frequency of microsatellite instability in the Arginine/Arginine، Arginine/ Proline and Proline/Proline genotypes were 14 (19. 2%)، 12 (38. 7%) and 3 (18. 8%) respectively. A significant difference in distribution of MSI was found for the Arginine/ Proline genotype compared with (grouped) Arginine/Arginine and Proline/ Proline genotypes (P=0. 028). Our findings suggested that breast invasive ductal carcinomas arisingin individuals with p53 codon 72 heterozygosity (Arginine/Proline) may be preferentially prone to microsatellite instability more than other genotypes.

Silk fibroin is a suitable protein for osteogenesis by inducing markers of bone formation in the cultures of osteoblasts, so we examined the ability of this protein to induce mineralized nodules in the rat bone marrow stromal cell cultures. Bone marrow stromal cells obtained from 4 to 6 weeks old Spruge-Dawely male rats were grown in primary culture for seven days and then subcultured for 21 days. The secondary cultures were done on either silk fibroin-coated polystyrene plates or free-silk fibroin ones. After 21 days of grow up, the cultures were examined for nodule formation by scanning electron microscopy, for mineralization by alizarin red S staining and for expression of gene markers of osteoblast maturation by reverse transcription PCR (RT-PCR). The stromal cells were observed to form three-dimensional nodules when cultured on the silk fibroin and compared to the stromal cells cultured on the free-silk fibroin polystyrene plates, where no nodules were observed in the time-frame studied. These nodules were also found to be mineralized and expressed the gene markers of osteoblast. Silk fibroin could serve as suitable inducing factor by stimulating stromal cell differentiation to form mineralized nodules. Iran. Biomed.