Two single nucleotide polymorphisms in the von Hippel-Lindau tumor suppressor gene in Taiwanese with renal cell carcinoma

Abstract

Background: Renal cell carcinoma, a common malignant tumor arising from the kidney, occurs in 3.62 and 1.95 cases per one hundred thousand people among men and women, respectively, in Taiwan each year. Approximately 80% of cases are classified as clear-cell renal cell carcinoma. Inactivation of the von Hippel-Lindau tumor suppressor gene has been implicated in the tumorigenic pathway of renal cell carcinoma. Two single nucleotide polymorphisms, rs779805 and rs1642742, located in the promoter and 3' untranslated regions of the von Hippel-Lindau gene are informative and implicated in the occurrence of renal cell carcinoma worldwide. The aim of this study is to clarify whether these polymorphisms are associated with renal cell carcinoma in Taiwanese. Genomic DNA was isolated from normal and tumor tissues of 19 renal cell carcinoma patients. The samples were screened for allelic polymorphisms by restriction fragment length polymorphism with BsaJ I and Acc I digestion. Reconfirmation was carried out by direct sequencing.

Results: Consistent with Knudson's two-hit theory, AA to AG somatic mutations were observed in rs779805. In addition, loss of heterozygosity in both rs779805 and rs1642742 was demonstrated in 10 out of 15 RCC patients aged 50 or over. The G allele or AG heterozygote frequencies at these two loci were much higher in patient germline DNA when compared with the control group. After adjusting for age, the frequency of the G allele in both loci was much higher for late onset renal cell carcinoma in the Taiwanese population.

Conclusions: Our current results confirmed that the existence of G allele in both rs779805 and rs1642742 in the von Hippel-Lindau tumor suppressor gene is of importance in renal cell carcinoma tumorigenesis. However, more comprehensive and detailed research is needed to address the clinical relevance. Larger sample size is required to determine the exact power of correlation between these two genetic polymorphisms and renal cell carcinoma.

Figure 1

Partial sequencing chromatograms of the VHL gene containing rs779805 in reverse direction from tumor tissues. The rs779805 is represented by a rectangular frame. (A), (C), and (E) represent examples of loss of heterozygosity (LOH) of the A allele at rs779805 of VHL gene in RCC patients (#1, #3, and #6 in Table 1). (B) and (D) represent loss of the G allele (#2 and #4). (F) is a heterozygote with two almost equal bands (#11).

Figure 2

Partial sequencing chromatograms of the VHL gene containing rs1642742 in reverse direction. The rs1642742 is represented by a rectangular frame. Normal tissue (A) and tumor tissue (B) from heterozygous individual #1 in Table 1 show LOH. (B) and (D) represent examples of LOH of the A allele at rs1642742 of VHL gene in the tumor tissues from RCC patients (#1 and #7). (C) represents loss of the G allele (#2).