By comparison, CXCL12-β and, to a greater extent, -γ have reduced binding affinities for receptors CXCR4 and CXCR7. Biochemical KU-60019 molecular weight differences in binding to receptors and extracellular matrix molecules translate

to different functional outcomes. In mouse models, CXCL12-γ promotes chemotaxis of immune cells and endothelial progenitors to a significantly greater extent than other isoforms [53] and [54]. Greater binding to heparan sulfates and extracellular matrix molecules also limits proteolytic degradation of CXCL12 [55]. These studies highlight functional differences among CXCL12 isoforms in receptor binding, chemotaxis, and stability that could alter outcomes in breast cancer. Our data also support further studies analyzing functional differences among CXCL12 isoforms, especially for CXCL12-δ. Correlation between gene transcript data and protein expression is dependent on the gene and tissue type. However, mRNA expression is generally a good proxy for protein expression and is frequently used as biomarkers.[56], [57] and [58] Gene expression also forms the basis of the PAM50 molecular subtyping of breast cancer as well as Oncotype Dx, a widely used predictive model for chemotherapy

response in breast cancer.[59], [60], [61] and [62] Specifically for CXCL12-α, -β, and -γ, mRNA levels as measured by quantitative reverse transcription–polymerase chain reaction correlate with protein levels as measured by ELISA.[63] Z-VAD-FMK price We also recognize that this study has limitations based on the data publicly available through the TCGA. While the data set contains transcript data for a large number of patients, the median follow-up time is relatively short, and therefore, the number of metastasis and recurrence events is small, thus limiting our statistical power. This likely accounts for why the P values for CXCL12-δ MFS and RFS do not reach significance.

We also do not know the full treatment history for all patients, such as exact chemotherapy and radiation regimens, and there is likely significant heterogeneity in treatments given the multi-institutional nature of the data. Even with these limitations, we were able to identify significant differences in outcomes for isoforms of CXCL12. Metalloexopeptidase In summary, our data reveal new associations of CXCL12, CXCR4, and CXCR7 gene expression with molecular, histologic, and clinical categories of human breast cancer. In addition, we have identified isoform-specific differences in CXCL12 for outcomes in breast cancer, suggesting distinct biochemical functions of isoforms in disease progression. These compelling results establish the foundation for mechanistic preclinical studies of these isoforms in breast cancer. Additional studies are also warranted to elucidate the biologic and functional differences between the CXCL12 isoforms and validate them as potential biomarkers. The following are the supplementary data related to this article.