Abstract P1-07-22: Investigating the role of Duffy antigen receptor for chemokines (DARC) isoforms in breast cancer metastasis
Authors: Hire Rupali , Walens Andrea , Bennett Brianna , Mumin Kauthar , Campbell Hailey , Lou Michael , Monteil Michele , Howerth Elizabeth , Davis Melissa 
Published: May 2015

Duffy Antigen Receptor for chemokines (DARC) is known to regulate the biological activities of chemokines. It has been implicated in the progression of various diseases including different types of cancer, affecting survival, proliferation and metastasis. Genetic variants in the DARC genes are strongly associated with African ancestry and are linked to malaria resistance. There are at least two isoforms of DARC, which have not been appreciably investigated in these contexts, that may have differing chemokine activity functions. To fill this knowledge gap, we have been characterizing the impact of DARC gene variants on DARC isoform expression in specific tissue types in order to define relationships between the polymorphic DARC and its effect as an immune regulator in breast cancers. We hypothesize that DARC variants, which are known to impact expression of the gene on erythrocytes, also are associated with functional activity related to DARC’s control of metastatic potential in breast cancer. Specifically, we have determined that one DARC polymorphism which is well defined in ancestral groups (i.e. Duffy null - rs2814778; -541T&gt;C) is associated with differential expression of DARC isoforms in epithelial cell types, including lymphoblast and breast tissues.

We investigated the erythroid silencing Duffy Null allele of DARC using DNA sequencing and quantitated DARC isoform expression by real time PCR in breast cancer cell lines, ancestral cell lines and breast cancer tumor tissues. We will show that DARC isoforms have significantly variant expression among ancestral groups that is associated with the Duffy Null allele. We will also show that certain types of breast tumors have variable DARC expression that is also associated with this genotype. Additionally, we visualized the subcellular localization of DARC and known interacting chemokines breast cancer cells with IHC and IF confocal microscopy.

Specifically, our results indicate breast tumors differentially express DARC in which may be affecting the chemokine pool and immune response within the tumor and its microenvironment. In our Hapmap ancestral populations, all DARC genotypes expressed the gene in lymphoblast, with significantly different levels of isoforms among African, African American and European individuals. Breast cancer cells also show different levels of specific DARC isoform mRNA levels and distinct levels and patterns of binding chemokines, related to tumor subtype origins (i.e. ER status).

Based on these findings we conclude that DARC isoforms have differential expression levels in breast cancer cells within tumor and non-tumor regions that may drive both pro and anti tumorigenic events with varying chemokine binding or localizations during tumorigenesis of specific breast cancer subtypes. Different levels of isoforms in epithelial cells may contribute to its essential function as atypical chemokine receptor. We hypothesize that immune responses in breast cancer patients with Duffy Null genotypes will differ and may express more severe metastasis due to altered epithelial regulation of alternate DARC isoforms.

Citation Format: Rupali Hire, Andrea Walens, Brianna Bennett, Kauthar Mumin, Hailey Campbell, Michael Lou, Michele Monteil, Elizabeth Howerth, Melissa Davis. Investigating the role of Duffy antigen receptor for chemokines (DARC) isoforms in breast cancer metastasis [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-22.