Abstract A049: Centrosome loss and chromosomal instability in prostate tumor progression
Authors: Wang Mengdie , Knudsen Beatrice S. , Rogers Gregory C. , Cress Anne E. 
Published: February 2019

Background: Chromosomal instability is a hallmark of cancer. Early genomic events in tumor progression include copy number variations such as tandem duplications and deletions that involve at least &gt;100kB stretches of DNA. Although single-driver mutations are remarkably infrequent in most cancers (e.g., accounting for only 2-3% of human epithelial cancers), approximately 20% of prostate tumors are reported to display chromothripsis. Errors in mitotic chromosome segregation produce micronuclei that are susceptible to chromothripsis, and this can occur due to changes in centrosome numbers. Centrosomes are organelles that nucleate microtubule growth and, thus, determine the number of mitotic spindle poles. Normally, mitotic cells contain two centrosomes that guide formation of a bipolar spindle, ensuring that daughter cells divide within the epithelial plane and inherit an equal complement of the genome. Centrioles are the duplicating elements of centrosomes, and their loss or overduplication (known as “amplification”) promotes spindle assembly defects that lead to chromothripsis. Precise control of centriole copy number is vital in order to maintain genomic stability and normal tissue homeostasis.

Methods: We developed an assay for the detection and quantitation of centrosome numbers in FFPE normal and cancer tissue and tissue culture cell lines. In addition, a 3D culture model of an immortalized nontumorigenic prostate epithelial cell line (RWPE-1) was used to characterize the progression of prostate spheroids from normal gland to high-grade prostatic intraepithelial neoplasia (HG-PIN) type structures in vitro. Genomic instability was detected by polyploidy (flow and metaphase analysis), SKY (Roswell Park Cancer Institute Cytogenetics SKY core laboratory), and micronuclei formation. Chromosome fragility was assessed by time-lapse microscopy.

Results: Human prostate cancer has a readily detectable centrosome dysfunction that occurs early in the disease progression. Whereas triple-negative breast cancer specimens contained centrosome amplification as expected, surprisingly, centrosome loss was detected in early-stage prostate cancer (Gleason stage 3+3, 3+4 and 4+4) tissue specimens and in AR-positive cell lines (LnCAP, VCaP). We note that centrosome amplification was observed in AR-negative cell lines (DU145, PC3 and H660). Using TCGA data, twelve centriolar genes were either amplified, deleted, or mutated in prostate adenocarcinoma and metastatic disease. In contrast, all twelve centriolar genes were highly amplified in neuroendocrine prostate cancer.

Using centrinone, a small-molecule inhibitor of Polo-like kinase 4, we blocked centriole duplication in nontumorigenic prostate cells (RWPE-1). Centrinone treatment resulted in significant genomic instability (polyploidy, copy number variation across all chromosomes, and micronuclei formation) and mitotic errors (increased mitotic index, prolonged mitosis, and increased chromosome fragility). Additionally, centrosome loss produced prostate cancer-specific phenotypes (erg overexpression, TMPRSS2 amplification, and invasive budding).

Conclusions: The loss of centrosomes during early stages of prostate cancer development may account for the increased chromosomal instability manifested as polyploidy and copy number variations. Whether alterations in centrosome numbers occur in high-grade prostate cancer or metastatic lesions is unknown. Centrosomes may be promising biomarkers for advancing disease but also rational targets for personalized therapy in prostate cancer. (Supported in part by NIH grants CA 23074, CA 159406 and NIGMS R01GFM110166.)

Citation Format: Mengdie Wang, Beatrice S. Knudsen, Gregory C. Rogers, Anne E. Cress. Centrosome loss and chromosomal instability in prostate tumor progression [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A049.