RESUMEN
The tumor suppressor gene TP53 is the most commonly mutated gene in human cancer. The reported prevalence of mutations in rhabdomyosarcoma (RMS) varies widely, with recent larger studies suggesting that TP53 mutations in pediatric RMS may be extremely rare. Overexpression of MDM2 also attenuates p53 function. We have performed TP53 mutation/MDM2 amplification analyses in the largest series analyzed thus far, including DNA isolated from 37 alveolar and 38 embryonal RMS tumor samples obtained from the Cooperative Human Tissue Network (CHTN). Available samples were frozen tumor tissues (N = 48) and histopathology slides. TP53 mutations in exons 4-9 were analyzed by direct sequencing in all samples, and MDM2 amplification analysis was performed by differential PCR on a subset of 22 samples. We found only one sample (1/75, 1.3%) carrying a TP53 mutation at codon 259 (p.D259Y) and no MDM2 amplification. Two SNPs in the TP53 pathway, associated with accelerated tumor onset in germline TP53 mutation carriers, (TP53 SNP72 (rs no. 1042522) and MDM2 SNP309 (rs no. 2279744)), were not found to confer earlier tumor onset. In conclusion, we confirm the extremely low prevalence of TP53 mutations/MDM2 amplifications in pediatric RMS (1.33% and 0%, respectively). The possible inactivation of p53 function by other mechanisms thus remains to be elucidated.
RESUMEN
Hepatocellular Carcinoma (HCC) is a leading cause of cancer-related death worldwide. Globally, the most important HCC risk factors are Hepatitis B Virus (HBV) and/or Hepatitis C Virus (HCV), chronic alcoholism, and dietary exposure to aflatoxins. We have described the epidemiological pattern of 202 HCC samples obtained from Colombian patients. Additionally we investigated HBV/HCV infections and TP53 mutations in 49 of these HCC cases. HBV biomarkers were detected in 58.1% of the cases; HBV genotypes F and D were characterized in three of the samples. The HCV biomarker was detected in 37% of the samples while HBV/HCV coinfection was found in 19.2%. Among TP53 mutations, 10.5% occur at the common aflatoxin mutation hotspot, codon 249. No data regarding chronic alcoholism was available from the cases. In conclusion, in this first study of HCC and biomarkers in a Colombian population, the main HCC risk factor was HBV infection.
RESUMEN
The p53 tumor suppressor gene (TP53; OMIM: 191170) plays an important role in tumorigenesis in lung epithelial cells. TP53 encodes a sequence-specific DNA-binding protein that regulates transcription of several genes in response to DNA damage promoting cell cycle arrest, DNA repair or apoptosis. A mutation does not necessarily alter the protein function and since not all altered tumor protein p53 (TP53) conformations lead to the same biological properties, we studied Cys135Arg TP53 gene mutation in squamous cell type of non-small cell lung cancers (NSCLCs), by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and direct sequencing. Cys135Arg TP53 mutation, rare in databases (11/23544 in R11, IARC TP53 database), was detected. We chose p.C135R in order to examine DNA-TP53 interaction. A comparison with the wild-type after 1 nano-second molecular dynamic simulation analysis revealed a significant structural change (over 4A displacement) in the contact loop Lys-Ser-Val which lies upstream and next to the mutated site in the TP53, that sterically prevents its DNA-binding activity. Additionally, the mutation produced a change in the electrostatic potential surface of the protein in the same loop where the structural modification took place. To demonstrate the degree of loss of function, functional assays in yeast and bacteria with oligonucleotides for competitive electrophoretic mobility shift assays (EMSAs) were done proving that this mutation decreases TP53 ability to bind DNA of the TP53 response element from the human p21 gene. These results demonstrate that the amino acid change C135R in the human TP53 generates the loss of TP53 DNA-binding activity directly affecting its role as a transcription factor and suggests that this observation can explain part of the phenotype described in patients affected by this type of tumor.
