Common variations in TERT-CLPTM1L locus are reproducibly associated with the risk of nasopharyngeal carcinoma in Chinese populations

Abstract

Associations between single nucleotide polymorphisms (SNPs) at 5p15 (TERT-CLPTM1L) and multiple cancer types have been reported. We examined whether polymorphisms in the TERT-CLPTM1L locus were related to the risk of developing nasopharyngeal carcinoma (NPC) among Chinese populations. In the first stage, 26 tag SNPs were genotyped in a Guangxi population (855 patients and 1036 controls). In the second stage, the SNPs, which showed significant association, were further genotyped in a Guangdong population (997 patients and 972 controls). Functional analyses were conducted to verify the biological relevance of the associated polymorphism. In the 1st stage, four SNPs (rs2736098, rs2735845, rs402710, and rs401681) were significantly associated with the risk of developing NPC. After the 2nd stage validation, rs2735845 and rs401681 were independently associated with the risk of developing NPC in the additive model (rs2735845, OR = 1.19, 95% CI = 1.04-1.37, P = 0.011; rs401681, OR = 0.85, 95% CI = 0.74-0.99, P = 0.034). Furthermore, we observed higher CLPTM1L messenger RNA levels in fetal mesenchymal stem cells from the rs2735845 G allele carriers compared with that from non-carriers. In addition, using an immunohistochemistry assay, we observed higher TERT and CLPTM1L levels in NPC tissues compared with that in non-cancerous nasopharyngeal tissues. Our findings suggest that polymorphisms in the TERT-CLPTM1L locus may play a role in mediating the susceptibility to NPC in Chinese populations.

Keywords: CLPTM1L; TERT; nasopharyngeal carcinoma; polymorphism.

Figure 1. Regional plots for associations at the TERT-CLPTM1L locus on chromosome 5p15.33

(A) Significance of the each tag SNPs. Shown are the −log₁₀ association P values of SNPs in the Guangxi population. The intensity of the red shading indicates the strength of the linkage disequilibrium (LD) with the index SNP (rs2735845). Also shown are the SNP built 36 coordinates in kilobases (kb), the recombination rates in centimorgans (cM) per megabase (Mb) (in blue) and the genes in the region (in green). (B) Pairwise LD between tag SNPs at the TERT-CLPTM1L locus. The value within each diamond represents the pairwise correlation between tag SNPs (measured as D’) defined by the upper left and the upper right sides of the diamond. The diamond without a number corresponds to D’ = 1. Shading represents the magnitude and significance of pairwise LD, with a red-to-white gradient reflecting higher to lower LD values.

Figure 2. Quantitative real-time RT-PCR for CLPTM1L

The expression of CLPTM1L for three different genotypes of rs2735845 was measured in RNA from fetal mesenchymal stem cells from human umbilical cord obtained from a group of 12 normal full-term-delivery women. Normalization for mRNA quantity was performed with human GAPDH control primers for each sample, and the final abundance values were adjusted to yield an arbitrary value of 1 for the rs2735845 CC genotype. Columns include the mean from triplicate measurements; the vertical bars indicate the standard deviation. Compared to the CC carriers, the G allele carriers exhibited markedly elevated CLPTM1L transcription (P = 0.02; t test).

Figure 3. Protein expression of TERT and CLPTM1L by immunohistochemical staining in representative nasopharyngeal carcinoma tissues and non-tumor nasopharyngeal tissues

Images in the box (left, 100×) were enlarged and are shown in the right box (400×). The scale bar represents 50 μm.