BIALLELIC INACTIVATION OF THE VON HIPPEL-LINDAU TUMOR SUPPRESSOR GENE IN SPORADIC RENAL CELL CARCINOMA

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Abstract
Somatic mutations of the von Hippel-Lindau tumor suppressor gene VHL and loss of heterozygosity of 3p25 to 26 have been well analyzed in renal cell carcinoma but it is not yet clear how often complete biallelic inactivation of VHL occurs in sporadic renal cell carcinoma. We improved the estimation of loss of heterozygosity of VHL and examined 2-hit inactivation of VHL based on loss of heterozygosity, mutation and methylation of sporadic renal cell carcinoma. DNA extracted from 59 Japanese sporadic renal cell carcinoma samples containing clear cells was examined for loss of heterozygosity of 4 intragenic markers of single nucleotide polymorphism and 2 extragenic microsatellite markers. Mutation was analyzed by sequencing amplified VHL DNA and methylation was analyzed by methylation specific polymerase chain reaction. Four intragenic markers showed loss of heterozygosity in 13 of 22 samples (59.1%), whereas the 2 extragenic markers D3S1560 and D3S1317 showed loss of heterozygosity in 15 of 46 (32.6%) and 11 of 49 (22.4%), respectively. Considering loss of heterozygosity in 14 renal cell carcinomas informative at all 3 loci the incidence of loss of heterozygosity of VHL in renal cell carcinoma was estimated to be 73.5% or 25 of 34 cases. Mutations in VHL were found in 25 of 59 renal cell carcinomas (42.4%) and frame shift mutations in 68% of all mutations often occurred at nucleotide repeat sequences. Of the 34 loss of heterozygosity informative renal cell carcinoma 15 (44.1%) had 2-hit inactivation of VHL and 11 (32.4%) had 1-hit inactivation. The frequency of biallelic inactivation of VHL in sporadic renal cell carcinomas was unexpectedly low. According to the 2-hit theory of tumor suppressor genes another hit in VHL that to our knowledge remains unknown to date is thought to be involved in the development of renal cell carcinoma.