Functional polymorphism in the 5'-UTR of CR2 is associated with susceptibility to nasopharyngeal carcinoma

Abstract

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is a squamous cell cancer endemic in Southern China and Southeast Asia. It has been shown that inflammatory and immune responses during EBV infection contribute to the development of NPC. The complement receptor 2 (CR2) gene plays central roles during inflammatory and immune responses and, therefore, is a good candidate susceptibility gene for NPC. We performed PCR-based sequencing to identify multiple single-nucleotide polymorphisms (SNPs) within the exon regions of the CR2 gene in a Cantonese population. Two SNPs were screened in 528 NPC patients and 408 normal individuals to perform a case-control study matched according to age, gender and residence. Furthermore, we cloned the entire 5'-UTR and entire CR2 promoter into a luciferase report system and compared the luciferase activities between the different allelic constructs. A SNP in the 5'-UTR of CR2 (24 T/C, rs3813946) showed a significant association (P<0.01) with NPC in the Cantonese population studied. The subjects were categorized into 2 age groups: group 1, age ≤45 years and group 2, age >45 years. In group 1, the allelic frequencies of 24 T/C in the patients were significantly different from those of the controls (P=0.0034). The odds ratio (OR=1.81) also indicated a higher risk of NPC in individuals who carried the minor allele C. All constructs exerted allelic differences on luciferase activities, but only the susceptible allele +24C construct showed increased activity. Our findings implicate CR2 as a susceptibility gene for NPC and suggest that enhanced CR2 expression may be involved in the oncogenesis and development of NPC.

Figure 1

Transcriptional effects of SNP 24T/C by expression of reporter luciferase gene activity. (A) Transcription factor binding sites within the proximal CR2 promoter critical for regulation of basal transcription (32). Shown are nucleotide positions and the functional role of localized elements, TATA box, transcriptional initiation site and position of SNP 24T/C. (B) Transcriptional activity of constructs expressing the major or minor 24T/C SNP allele. Results shown represent mean promoter activity ± SE and are expressed as normalized transcriptional activity of recombinant constructs with P group and U group 60 h after transfection. Expression of the minor +24 C allele resulted in a marked increase in transcriptional activity compared with expression of the major T allele in the two groups (P<0.05). The experiments were repeated 3 times (n=3).