Jin, Fang

Abstract During mitosis, sister chromatids are separated and equally divided over two daughter cells. If missegregation of whole chromosomes occurs, progeny cells with an abnormal number of chromosomes will arise. This is referred to as aneuploidy, a hallmark of most human cancers. We found that inactivation of a single Pten allele in mouse splenocytes and mouse embryonic fibroblasts (MEFs) is sufficient to cause aneuploidy, suggesting a role for Pten in the chromosome segregation process. Upon further study by live cell imaging of haploinsufficient and null Pten MEFs, we indeed found many missegregation errors (59% and 79% respectively, compared to 15% in wildtype MEFs). These abnormalities were independent from the AKT pathway since overexpression of a myristoylated, constitutively active form of AKT in wildtype MEFs resembled a wildtype instead of a Pten heterozygous phenotype. In addition, overexpression of a catalytic mutant Pten (C124S) in Pten+/- MEFs corrected the missegregation errors. We therefore propose a novel tumor-suppressive function of Pten to prevent whole chromosome instability, independent of the increased cell proliferation and survival caused by the activation of AKT. BubR1 is a regulator of kinetochore-microtubule attachment and a potent inhibitor of Cdc20, a key co-activator of the anaphase promoting complex/cyclosome (APC/C) that drives cells into anaphase by targeting the anaphase inhibitors cyclin B1 and securin for degradation by the 26S proteosome. We found that overexpression of BubR1 completely restores accurate chromosome segregation in Pten+/- MEFs, alluding to a specific role for Pten in mitosis. As a first step to test the hypothesis that Pten's mitotic role in preventing aneuploidization represents a key tumor suppressive function of this phosphatase, we bred a Flag-tagged BubR1 transgene into Pten+/- mice. We are currently in the process of studying the impact of the transgene on the development of prostatic intraepithelial neoplasia (PIN). Consistent with our hypothesis, preliminary analysis of two mice shows that BubR1 overexpression considerably decreases PIN lesion multiplicity. Data from the complete analysis of our double transgenic mouse cohort will be presented at the meeting. 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 2992. doi:10.1158/1538-7445.AM2011-2992

Cdc20 is an activator of the anaphase-promoting complex/cyclosome that initiates anaphase onset by ordering the destruction of cyclin B1 and securin in metaphase. To study the physiological significance of Cdc20 in higher eukaryotes, we generated hypomorphic mice that express small amounts of this essential cell cycle regulator. In this study, we show that these mice are healthy and not prone to cancer despite substantial aneuploidy. Cdc20 hypomorphism causes chromatin bridging and chromosome misalignment, revealing a requirement for Cdc20 in efficient sister chromosome separation and chromosome–microtubule attachment. We find that cyclin B1 is newly synthesized during mitosis via cytoplasmic polyadenylation element–binding protein-dependent translation, causing its rapid accumulation between prometaphase and metaphase of Cdc20 hypomorphic cells. Anaphase onset is significantly delayed in Cdc20 hypomorphic cells but not when translation is inhibited during mitosis. These data reveal that Cdc20 is particularly rate limiting for cyclin B1 destruction because of regulated de novo synthesis of this cyclin after prometaphase onset.

Abstract ETS variant 1 (ETV1), also known as ETS-related protein 81, is overexpressed in prostate tumors, but whether and how this transcription factor affects tumorigenesis has remained elusive. Here, we show that ETV1 is primarily overexpressed in the most aggressive human prostate tumors. Transgenic ETV1 mice developed prostatic intraepithelial neoplasia as well as hyperplasia/neoplasia in seminal vesicles. Moreover, ETV1 cooperated with the androgen receptor (AR) to bind to the prostate-specific antigen enhancer and stimulate gene transcription. Consistent with its ability to physically interact with AR, ETV1 rendered an ETV1 binding site–driven reporter androgen inducible, and, on the other hand, ETV1 superinduced transcription from an AR binding site on androgen stimulation. In conclusion, our study substantiates that ETV1 overexpression is an underlying cause in the development of prostate and possibly also seminal vesicle cancer. Its interaction with and activation of AR provides a molecular mechanism on how ETV1 exerts its deleterious function. Thus, inhibiting ETV1 or blocking its interaction with AR may represent novel strategies in prostate cancer therapy. [Cancer Res 2009;69(20):8102–10]