Abstract 248: Control of prostate tumor growth and centriole amplification by antizyme and antizyme inhibitor

Abstract

Abstract The endogenous antizyme inhibitor (AZI) is best characterized for its role in regulating polyamine homeostasis. Polyamines are organic cations synthesized by the enzyme ornithine decarboxylase (ODC), a protein which is negatively regulated and targeted for proteasomal degradation by antizyme (AZ). AZI is a potential oncogene which promotes cell growth not only by inhibiting antizyme (AZ) activity, but also by releasing ODC from AZ-mediated degradation. High levels of ODC and polyamines are associated with numerous types of neoplastic transformation, and the genomic region including AZI is frequently amplified in tumors of the ovary and prostate. To determine whether AZI functionally promotes prostate tumor growth, we made PC3M-LN4 (human) and AT6.1 (rat) cancer cell lines stably expressing AZI shRNA. AZI knockdown was confirmed by western blot and RT-PCR. To examine the ability of these cells to form tumors in vivo, 1×106 cells were injected subcutaneously into nude mice either with (PC3M-LN4) or without (AT6.1) Matrigel. Tumor growth was measured two times per week by caliper. Cells in which AZI levels had been knocked down by shRNA formed significantly smaller tumors in vivo, and had significantly smaller end tumor weights. These results suggest that not only does AZI promote tumor growth, but also that AZI may be a novel and valid therapeutic target for cancer treatment. In addition to their effects on cell proliferation, previous studies in our laboratory have shown that both AZI and AZ localize to centrosomes and are important for controlling centrosome duplication. Centrosome amplification is a frequent and early event in tumorigenesis. We found that overexpression of AZI and knockdown of AZ both result in cells with daughter centriole amplification due to abnormal centriole synthesis. To gain insight into the mechanism by which AZ and AZI modulate centriole synthesis, we are currently analyzing whether proteins that regulate centrosome duplication interact with either AZI or AZ. We are also using Tet-inducible overexpression vectors to monitor the effect of increased AZ or AZI levels on centriole amplification, and exploring how localization of these proteins to the centrosome contributes to the centrosome amplification phenotype. These studies provide a much greater understanding of AZI function, and suggest that high AZI levels may contribute to tumorigenesis both by promoting cell growth and inducing centrosome amplification. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 248. doi:10.1158/1538-7445.AM2011-248