Regulation of pluripotency genes by CX3CR1 in cancer cells

Abstract

Prostate and breast cancers are among the most frequently diagnosed malignancies in the United States, leading to approximately 60,000 deaths every year. Although localized disease has a high survival rate, over 30% of the patients with either form of tumor develop metastatic recurrence over time. Metastatic disease remains incurable, accounting for most cancer-related deaths. Evidence suggests that while most cancer cells within a primary tumor lack the ability to initiate new tumors, a small group of cells known as cancer stem cells (CSCs) can initiate metastatic lesions and sustain their growth. CSCs are characterized by stemness features, which are mediated by the expression of pluripotency transcription factors, including OCT4a and NANOG. Recent evidence suggests that chemokine receptors may play an important role in the regulation of cell stemness. Our lab has previously demonstrated that the chemokine receptor CX3CR1 is implicated in tumor progression and metastasis in prostate and breast cancers. Furthermore, our studies suggest that prostate and breast cancer cells with high CX3CR1 expression (CX3CR1High) display stem-like features and express pluripotency genes. In contrast, cancer cells with low CX3CR1 expression (CX3CR1Low) do not display stemness features but undergo phenotypic plasticity, reacquiring the expression of CX3CR1 and pluripotency genes over a period of time. In this study, we set to determine if CX3CR1 is involved in regulating the expression of pluripotency genes during phenotypic plasticity. To this end, we used flow cytometry to sort prostate and breast cancer cells based on their CX3CR1 expression levels, and then cultured CX3CR1Low cells over a period of time to assess the timeframe for the re-expression of CX3CR1, OCT4a and NANOG. We also cultured these cells in the presence of a CX3CR1 small molecule inhibitor, FX-68, in order to assess the effect of blocking CX3CR1 in the re-expression of pluripotency genes. Our preliminary results show that both prostate and breast cancer CX3CR1Low cells increase their expression of CX3CR1, OCT4a and NANOG following in vitro culture, and this re-expression appears to be impaired when CX3CR1 is blocked. These results suggest that CX3CR1 may be involved in regulating its own expression and the expression of pluripotency genes and may thus play a role in dictating stemness features and promoting metastasis initiation. Our study provides further evidence for the involvement of CX3CR1 in cancer progression and its potential as a therapeutic target to treat metastatic disease.