RelA driven co-expression of CXCL13 and CXCR5 is governed by a multifaceted transcriptional program regulating breast cancer progression.

Lethal metastasis of primary breast tumors to lymph nodes has been found to be associated with the co-expression of chemokine CXCL13 and its receptor CXCR5. To date, however, the precise molecular events regulating the co-expression of CXCL13 and CXCR5 in the context of breast cancer progression have not been identified. Therefore, to extend our understanding of the drivers of breast cancer metastasis, we undertook a line of investigation in this study in which we demonstrate that the transcriptional regulation of CXCL13 is mediated by the reciprocal activity of RelA and Nrf2, while CXCR5 is transcriptionally silenced by CpG island methylation within its promoter. Critically, we show that intra-tumoral CXCL13 and CXCR5 mRNA expression is positively correlated with intra-tumoral RelA expression within the primary tumor of breast cancer (BCa) patients (n = 98). We demonstrate a role for Nrf2 in the negative transcriptional regulation of cxcl13. Furthermore, using a luciferase assay and deletion analysis of the cxcl13 gene promoter, we demonstrate that RelA and Nrf2 directly act upon the cxcl13 promoter to regulate transcription. Chromatin immunoprecipitation PCR, supported by in silico docking analyses, confirmed that RelA and Nrf2 both occupy multiple positions within the cxcl13 promoter. Collectively, in RelA high conditions, low Nrf2 and lack of cxcr5 promoter DNA-methylation govern CXCL13-CXCR5 co-expression within breast tumors, and thus drive disease progression and metastasis.