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Loss of heterozygosity and protein expression of APC gene in renal cell carcinomas

This study evaluated the potential contribution of the APC gene to malignant transformation in pateints with renal cell carcinoma. We tested 36 human renal cell carcinoma samples and 18 adjacent normal kidney tissues for the expression of APC protein, both wild and truncated types, by western blot method using antibodies that recognize either the carboxy or the amino epitope of the APC protein. The same tumor samples together with autologous peripheral blood were also analysed at the DNA level. Using specific oligonucleotide primers for exons 11 and 15, gene instability was followed by polymerase chain reaction/loss of heterozygosity (LOH) (on the basis of restriction fragment length polymorphism). Molecular data were also compared to pathohistological diagnosis, TNM stage and patient s age using multivariate statistical methods. All normal renal tissues express wild-type APC protein. Neither wild nor mutant type proteins were found in 36% (13/36) of tumor samples ; the rest of tumor tissues expressed the wild-type protein (312 kDa). Mutated APC protein, with a molecular weight of 117 kDa, was found in only one tumor sample. From 36 tumor samples 16 (44.4%) were informative for Rsa I exon 11 polymorphic site, while only half of these (8/16) demonstrated LOH. From 13 tumor samples that had no detectable protein product by western blot analysis 8 were homozygous for the exon 11 polymorphism and were tested for another polymorphic site, Msp I/exon 15. The overall proportion of LOH cases for both polymorphisms was 52.9% (9/17). 56% of samples with LOH show loss of the wild type APC protein expression. Pathohistological diagnosis showed no correlation with molecular data. However, multivariate analysis indicated strong positive correlation of age and TNM stage with the presence of LOH and the absence of the wild-type APC protein. Our results suggest that APC tumor suppressor gene plays a role in renal carcinogenesis. Alterations in this gene are responsible for tumor evolution and progression, but cannotbe considered as a first event in tumor initiation.

APC gene/protein; Loss of heterozygosity; Renal cell carcinomas

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