Immune Profile of Exosomes in African American Breast Cancer Patients Is Mediated by Kaiso/THBS1/CD47 Signaling

SIMPLE SUMMARY: African American (AA) women with breast cancer are more likely to have higher inflammation and a stronger overall immune response than European American (EA) women. In this report, we demonstrate the biological role of Kaiso in the immune signaling of breast cancer exosomes. Our findings indicate that Kaiso directly represses tumor suppressor THBS1, and this is associated with increased expression of CD47 and signal regulatory protein (SIRPA). Kaiso depletion attenuated tumor formation in athymic nude mice, and this is associated with increased infiltration of M1 macrophages. In vitro studies using THP1 cells that were treated with exosomes from Kaiso-depleted cells polarize towards the M1 phenotype with increased phagocytosis of cancer cells compared to high Kaiso control exosome, which polarizes towards an M2 phenotype. In summary, these findings reveal that Kaiso modulates the macrophage-mediated immune escape of cancer cells through exosome signaling, which may be related to poorer outcomes, especially for AA women. ABSTRACT: African American (AA) women with breast cancer are more likely to have higher inflammation and a stronger overall immune response, which correlate with poorer outcomes. In this report, we applied the nanostring immune panel to identify differences in inflammatory and immune gene expression by race. We observed a higher expression of multiple cytokines in AA patients compared to EA patients, with high expression of CD47, TGFB1, and NFKB1 associated with the transcriptional repressor Kaiso. To investigate the mechanism associated with this expression pattern, we observed that Kaiso depletion results in decreased expression of CD47, and its ligand SIRPA. Furthermore, Kaiso appears to directly bind to the methylated sequences of the THBS1 promotor and repress gene expression. Similarly, Kaiso depletion attenuated tumor formation in athymic nude mice, and these Kaiso-depleted xenograft tissues showed significantly higher phagocytosis and increased infiltration of M1 macrophages. In vitro validation using MCF7 and THP1 macrophages treated with Kaiso-depleted exosomes showed a reduced expression of immune-related markers (CD47 and SIRPA) and macrophage polarization towards the M1 phenotype compared to MCF7 cells treated with exosomes isolated from high-Kaiso cells. Lastly, analysis of TCGA breast cancer patient data demonstrates that this gene signature is most prominent in the basal-like subtype, which is more frequently observed in AA breast cancer patients.