Characterization of Hormone Receptor Positive Breast and Prostate Cancer Cell Response to Interleukin-1

Seventy percent of breast cancer (BCa) patients overexpress the hormone receptor (HR) estrogen receptor alpha (ER) which drives proliferation of these cells. Therefore, hormone therapy is used to target ER and block the growth of BCa tumor cells. Unfortunately, patients can develop resistance to hormone therapy through several mechanisms, including loss or reduced expression of ER. Additionally, there is a subpopulation of BCa patients who innately lack ER expression. Therefore, therapeutic targets alternative to ER must be identified and characterized. In the tumor microenvironment, immune cell infiltrates and cancer cells secrete inflammatory cytokine causing tumor inflammation. Interleukin-1 (IL-1) inflammatory cytokine is elevated in BCa patient serum and tumors and correlates with poor patient outcomes. In this work, we show that Interleukin-1 (IL-1) secreted by bone-derived immune cells is sufficient to repress ER expression in BCa cell lines; yet the cells remain viable through alternative survival pathways. Prostate cancer (PCa), which has similar etiology to BCa, is also driven by HR signaling. We previously discovered that concomitant with IL-1-induced repression of the PCa HR and therapeutic target, androgen receptor (AR), IL-1 upregulates the cytoprotective protein, Sequestome1 (p62); therefore, we sought to determine if BCa cells show a similar response to IL-1. p62 is a multidomain scaffolding protein that mediates several different prosurvival signaling pathways including autophagy and antioxidant signaling. We discovered that, indeed, IL-1 upregulates p62 in ER+ BCa cells. We had also previously discovered that p62 is basally high and cytoprotective for AR- PCa. Likewise, we found that cytoprotective p62 is basally high in ER- BCa cells. Taken together, we hypothesize that IL-1 induces a conserved signature in HR+ BCa and PCa cells that mimics basal gene expression in HR- BCa and PCa cells. Therefore, we performed RNA-sequencing on ER

• BCa cells exposed to IL-1 and compared the differential gene expression pattern to the basal expression in ER

• cells. Given the similar etiology of BCa and PCa, we overlapped our BCa dataset with our previously published RNA-sequencing PCa results and identified a 350 gene-signature comprised of genes that are induced or repressed by IL-1 in HR+ BCa and PCa and are respectively basally high or low in HR- BCa and PCa. Surveying the gene signature, we found two genes, p62 and SOX9, that have established roles in BCa and/or PCa initiation and/or progression and are elevated in BCa and PCa patient tissue. siRNA silencing showed that both p62 and SOX9 are required for HR- BCa and PCa cell survival. Furthermore, the FDA approved drug, verteporfin, which oligomerizes p62 rendering it non-functional, is cytotoxic for HR- BCa and PCa cell lines. The work herein provides mechanistic evidence for the role of inflammation in BCa and PCa treatment resistance, identifies a potential predictive and prognostic gene signature for treatment-resistant BCa and PCa, and provides therapeutic alternatives. Future studies include characterizing these alternative therapeutic targets identified in our 350-gene signature in BCa and PCa to provide much needed options for, currently, incurable patients