Abstract
Introduction: Aberrant mRNA stability for a number of genes coding for AU-rich (ARE) mRNAs, including chemokines and growth factors, occurs in many cancer types. The CXCR4-CXCL12 (SDF-1[alpha]) axis is among the most deregulated chemokine responses that promote the progression of invasive breast cancer. Normalization of the aberrant CXCR4-CXCL12 response by triggering CXCR4 ARE-mRNA destabilization mediated by the zinc finger mRNA binding protein, tristetraprolin (TTP, ZFP36), is a potential and intriguing approach. Methods: Several breast cancer cell lines were used for comparison with the MDA-MB-231 cell line as an invasive model of breast cancer. We treated the cells with a cell-permeable miR-29a inhibitor which triggers TTP expression, and monitored mRNA stability changes for key RNA binding proteins using RT-QPCR and reporter assays. RNA-immunoprecipitation was also employed to study the mRNA-protein interactions. Subsequent alterations in protein levels and associated functional attributes, including invasion and migration assays were investigated. Further, clinical data from a public database were used to understand these relationships. Results: We found that CXCR-4 over-expression in invasive breast cancer is causally linked to deficient TTP expression. TTP deficiency was partly due to the high miR-29a levels that target TTP 3'UTR- this is observed in the highly-invasive MDA-MB-231 cells when compared to other non-invasive or non-tumorigenic cell lines. We also show that CXCR-4 is an mRNA target for TTP but not its zinc finger mutant, C124R, as the wild type was able to bind to CXCR-4 mRNA.