Functional and genomic approaches reveal an ancient CHEK2 allele associated with breast cancer in the Ashkenazi Jewish population

Abstract

Functional and genomic approaches can be integrated to screen efficiently for pathogenic alleles in founder populations. We applied such approaches to analysis of the cancer-associated cell cycle regulator CHEK2 in the Ashkenazi Jewish population. We first identified two extended haplotypes at CHEK2 that co-segregated with breast cancer in high-risk families. We sequenced CHEK2 in a case representing each haplotype and discovered two novel amino acid substitutions, CHEK2.S428F in the kinase domain and CHEK2.P85L in the N-terminal region. To assay these alleles for loss of CHEK2 function, we tested their capacity to complement Rad53 deletion in Saccharomyces cerevisiae. CHEK2.S428F failed to complement Rad53 and thus largely abrogates normal CHEK2 function, whereas CHEK2.P85L complemented Rad53 as well as did wild-type CHEK2. Epidemiologic analyses were concordant with the functional tests. Frequencies of CHEK2.S428F heterozygotes were 2.88% (47/1632) among female breast cancer patients not selected for family history or age at diagnosis and 1.37% (23/1673) among controls (OR=2.13, 95% CI [1.26, 3.69], P=0.004), whereas frequencies of CHEK2.P85L were 0.92% among cases and 0.83% among controls. On the basis of the experience of mothers, sisters and daughters of probands, breast cancer risk due to CHEK2.S428F was estimated as 0.17 (+/-0.08) by age 60. We conclude that CHEK2.S428F increases breast cancer risk approximately 2-fold among Ashkenazi Jewish women, whereas CHEK2.P85L is a neutral allele. In general, these results suggest that selecting probands with extended haplotypes that co-segregate with disease can improve the efficiency of resequencing efforts and that quantitative complementation tests in yeast can be used to evaluate variants in genes with highly conserved function.

Germline mutations in the CHEK2 kinase gene are associated with an increased risk of bladder cancer

“…6,8,[12][13][14][15][16][17][18][19][20] CHEK2 is phosphorylated and regulated by the Ataxia Telangiectasia Mutated (ATM) kinase, another crucial mediator of cell cycle checkpoint control. 15,17 Cell cycle checkpoint control mechanisms are essential for the maintenance of genomic integrity but there appear to be differences in the efficiency of this process due to polymorphic variation, which have been suggested to contribute to oncogenesis.…”

“…Germline CHEK2 mutations have been associated with an increased risk of breast, prostate, colon cancers, thyroid, kidney, low-grade ovarian cancers and lymphomas, but bladder cancer has not been studied extensively. 1,11,[12][13][14][15][16]19,21,24,25 Two previous reports suggest that individuals with mutations in the CHEK2 gene might be at increased risk of bladder cancer. 13,14 To confirm this hypothesis, we have genotyped 416 incident cases of bladder cancer and 3,313 controls for the 4 CHEK2 founder mutations present in the Polish population.…”

“…12 Activation of CHEK2 in response to DNA damage is a signal to downstream targets in the checkpoint control pathways that include p53, Cdc25A, Cdc25C, BRCA1, E2F1, Pml1, Plk3 and other substrates whose biological functions become modified resulting in cell cycle blockade, enhanced DNA repair or apoptosis. 7,[12][13][14][15][16][17]19,21,22 The first mutations in CHEK2 which were reported in sporadic and hereditary cancers indicated that CHEK2 defects might explain the tumor-prone phenotype in families with Li-Fraumeni syndrome (LFS). 1,12,13,15,17,18,23 To date CHEK2 mutations have been found in subset of human breast carcinomas, testicular tumors and lymphomas.…”

Localization of breast cancer susceptibility loci by genome‐wide SNP linkage disequilibrium mapping

“…In our previous analysis of the ''field'' set, we determined that 4 of the 57 high-risk cases carried the CHK2 S438F mutation [Shaag et al, 2005]. Although a 9-locus haplotype TSC57163-TSC242417 on chromosome 22 that is less than 5 Mbs from the CHK2 locus obtained a P-value of 6 Â 10 À4 (data not shown), the associated haplotype was not carried by any of the S438F carriers.…”

“…This mutation is only slightly increased in frequency in unselected breast cancer cases in comparison to healthy population controls, but it is greatly increased among familial cases not carrying a BRCA1 or BRCA2 mutation [Meijers-Heijboer et al, 2002]. A CHK2 mutation specific to the Ashkenazi Jewish population was recently described [Shaag et al, 2005], and we investigated whether or not an association could be detected in our case series between the region that contains CHK2 and breast cancer.…”