Genomic organization and chromosomal localization of the humanCUL2 gene and the role of von Hippel-Lindau tumor suppressor-binding protein (CUL2 and VBP1) mutation and loss in renal-cell carcinoma development

Abstract

Germline mutations in the von Hippel-Lindau (VHL) disease tumor suppressor gene (TSG) convey a high risk of clear-cell renal-cell carcinoma (CC-RCC) and most sporadic CC-RCCs demonstrate somatic inactivation of the VHL TSG. However, the existence of further CC-RCC gatekeeper genes is implied by CC-RCC kindreds not linked to the VHL gene and the absence of somatic VHL inactivation in approximately 30% of sporadic CC-RCC. Genes that encode proteins which interact with the VHL gene product (VHL) provide candidate gatekeeper RCC genes. VHL forms a multimeric complex with two subunits (B and C) of the SIII (elongin) transcriptional elongation complex and CUL2, a member of the cullin family. Most pathogenic VHL mutations inhibit formation of the VHL/elonginB+C/CUL2 complex. A further VHL-binding protein of unknown function, VBP1, fails to bind to truncated forms of VHL. We have investigated the possible roles of CUL2 and VBP1 in renal tumorigenesis by analyzing sporadic RCC of known VHL mutation or hypermethylation status, including CC-RCC without VHL inactivation (n = 40); CC-RCC with VHL inactivation (n = 35); and non-CC-RCC (n = 14). No VBP1 mutations were identified in 89 sporadic RCCs, suggesting that VBP1 is not an RCC gatekeeper gene. To investigate CUL2, we mapped the CUL2 gene to chromosome band 10p11.1-p11.2, a region reported to show loss of heterozygosity (LOH) in several human cancers (including non-CC-RCC); determined the genomic organization; and performed mutation analysis of the 21 exons identified. Using novel intragenic polymorphisms, we detected LOH in 6/25 informative RCCs; however, no pathogenic CUL2 mutations were identified in the 89 RCCs analyzed. These findings suggest that unless CUL2 is inactivated by epigenetic events, it is not a major RCC TSG. However, CUL2 remains a candidate TSG for other tumor types demonstrating 10p LOH. Genes Chromosomes Cancer 26:20-28, 1999.