27-hydroxycholesterol impairs plasma membrane lipid raft signaling as evidenced by inhibition of IL6-JAK-STAT3 signaling in prostate cancer cells

We recently reported that restoring the CYP27A1-27hydroxycholesterol axis had anti-tumor properties. Thus we sought to determine the mechanism by which 27HC exerts its anti-PC effects. As cholesterol is a major component of membrane micro-domains known as lipid rafts, which localize receptors and facilitate cellular signaling, we hypothesized 27HC would impair lipid rafts, using the IL6-JAK-STAT3 axis as a model given its prominent role in PC. As revealed by single molecule imaging of DU145 PC cells, 27HC treatment significantly reduced detected cholesterol density on the plasma membranes. Further, 27HC treatment of constitutively active STAT3 DU145 PC cells reduced STAT3 activation and slowed tumor growth in vitro and in vivo. 27HC also blocked IL-6 mediated STAT3 phosphorylation in non-constitutively active STAT3 cells. Mechanistically, 27HC reduced STAT3 homodimerization, nuclear translocation and decreased STAT3 DNA occupancy at target gene promoters. Combined treatment with 27HC and STAT3 targeting molecules had additive and synergistic effects on proliferation and migration, respectively. Hallmark IL6-JAK-STAT gene signatures positively correlated with CYP27A1 gene expression in a large set of human metastatic castrate-resistant PCs and in an aggressive PC subtype. This suggest STAT3 activation may be a resistance mechanism for aggressive PCs that retain CYP27A1 expression. In summary, our study establishes a key mechanism by which 27HC inhibits PC is by disrupting lipid rafts as evidence by blocking of STAT3 activation. Implications: Collectively, these data show that modulation of intracellular cholesterol by 27HC can inhibit IL6-JAK-STAT signaling and may synergize with STAT3 targeted compounds.