Abstract 371: Hypoxia-induced centrosome loss as a driver of chromosomal instability in prostate cancer

Abstract PURPOSE: This study aims to identify a causal mechanism of centrosome loss previously observed in primary prostate cancer. Prostate cancer progression is accompanied by bursts of chromosomal instability (CIN), including chromosomal translocations, oncogene amplifications, and chromothripsis. While high CIN correlates with most metrics of aggressive disease, we lack a mechanistic understanding of how CIN originates in prostate cancer. Recently, we discovered that cells in primary prostate tumors lack centrosomes, cytoplasmic organelles that ensure the fidelity of chromosome segregation by organizing the shape of the mitotic spindle. Experimental elimination of centrosomes in immortalized, non-tumorigenic prostate cell lines was sufficient to generate extensive CIN, resulting in oncogenic transformation of these lines when sub-cutaneously injected into NSG mice. Because we identified centrosome loss as a potential driver of CIN, we sought to understand mechanisms that can trigger centrosome loss in the prostate. Although centrosome loss naturally occurs during the development of some tissues, for example centrosome elimination during oogenesis, the mechanisms that trigger loss are not known. Therefore, we first investigated microenvironmental changes in early prostate cancer as a potential cause. Hypoxia, pathologically low oxygen concentration, is common in the aging prostate due to loss of vasculature and is associated with poor prostate cancer prognosis and high CIN. Therefore, we hypothesized that hypoxic exposure induces centrosome loss in prostate cells. Indeed, we found that exposure to 1% oxygen concentrations leads to progressive centrosome loss in non-tumorigenic, immortalized prostate epithelial cell lines. Using immunofluorescence of centrosomes in cultured cells, we found that hypoxia-induced centrosome loss is independent of HIF transcription but requires activation of the confluence-dependent Hippo signaling pathway. Mechanistically, we found that centrosome disassembly begins with the removal of the pericentriolar material (PCM), the outer shell of the centrosome that nucleates microtubules. We were able to block centrosome disassembly by over-expressing a constitutively-active mutant of Polo-like Kinase 1, which normally strengthens the PCM during mitosis to promote centrosome maturation. Furthermore, centrosome loss was prevented by treatment with the Protein Phosphatase 2A (PP2A) inhibitor Okadaic Acid. Using RNAseq, we have identified potential PP2A regulatory subunits that are up-regulated in cells undergoing hypoxia-induced centrosome loss. Our model is that hypoxia induces dephosphorylation of the PCM, mechanically weakening the centrosome and leaving it vulnerable to disassembly. Together with previous findings, we conclude that hypoxia-induced centrosome disassembly is a plausible driver of CIN in early prostate cancer. Citation Format: John M. Ryniawec, Gregory C. Rogers, Anne E. Cress. Hypoxia-induced centrosome loss as a driver of chromosomal instability in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 371.