Association analysis and allelic distribution of deletion in CC chemokine receptor 5 gene (CCR5Δ32) among breast cancer patients of Pakistan

Abstract

Chemokine CC receptor type 5 (CCR5) is a cell surface receptor that has high affinity for chemotropic cytokines called chemokines. The CCR5 gene contains a 32 base pairs (bp) deletion (CCR5Δ32). This deletion may result in a malformed and nonfunctional receptor, reported to be responsible for the development and dissemination of different cancers. CCR5Δ32 exists in two allelic forms i.e. deletion (D) and wild type (WT). This study aims to detect the role of CCR5Δ32 in breast cancer development. Blood samples were collected from breast cancer patients (330) and controls of same gender (306). Along with this histopathologically diagnosed malignant tissue samples were also excised from breast lesions of 100 patients. Genetic variations within the blood and tissue samples were examined by PCR then observed through gel electrophoresis and confirmed by direct DNA sequencing. Obtained DNA sequences were aligned and analyzed by MEGA6 software. Genotypic and association analyses were done by SPSS software version 17.0. Deletion of 32 bp in CCR5 gene has been analyzed. Genotypic variations of CCR5Δ32 are; homozygous wild type (WT/WT), heterozygous deletion (WT/D) and homozygous deletion (D/D). Statistical analyses of CCR5Δ32 data revealed that WT/D was significantly higher in blood samples of breast cancer patients (7.27% (24/330)) as compare to controls (1.30% (4/306)). In tumor tissue samples WT/WT being the most frequent genotype (99.00% (99/100)) with 1.00 (1/100) of D/D which suggested that it may be acquired. Hence, association analysis showed that CCR5Δ32 is positively associated with breast cancer in Pakistan (p < 0.001). The risk ratio of CCR5Δ32 was 5.6610 (95% confidence interval: 2.0377 to 15.7267) and odds ratio was calculated to be 6.0335 (95% confidence interval: 2.1288 to 17.0999) which signifies that deletion also increases the risk of breast cancer development. Moreover, association analyses also revealed that clinicopathological features do not have any impact on the CCR5Δ32 genotype of breast cancer. This suggests that deletion of 32 bp in CCR5 gene may be associated with breast cancer. CCR5 signals the activation and migration of immune cells at the site of tumor formation. Because of deletion; deformed CCR5 receptor might be unable to express and function properly which may subdue the immunity against cancer hence, leading to its progression.

Keywords: 32 bp deletion; Breast cancer; CCR5 gene; Chemokines receptor; Metastasis.