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In order to better understand the molecular basis of prostatic tumors, the CAGE-Cancer project, recently undertaken by the University of São Paulo, Brazil, searched for and identified several induced genes in high graded prostatic carcinoma (Reis et al, 2004), among which was PPM1D (protein phosphatase dependent of magnesium 1D), a member of PP2C family. PPM1D encodes a serine/threonine phosphatase of ubiquitous expression, nuclear localization and a well known modulation by p53 upon cell stress. PPM1D is also associated with cell cycle progression through dephosphorylation and inactivation of p38MAPK, resulting in downregulation of several tumor suppressor genes, such as p53, p16INK4a and p14ARF. To asses whether PPM1D induction is a general mechanism of cell transformation, we quantified PPM1D expression in a panel of cell lines composed by five distinct tissues. In all cases, we observed higher PPM1D expression in more transformed cell lines, suggesting its oncogenic potencial for many different cell models. It is well known that androgens are important for prostate proliferation, development and tumor progression, therefore we decided to analyze PPM1D expression in the LNCaP prostate cell line after treatment, for different periods of time, with synthetic androgen (R1881). Ours results show that after a 4h treatment, it was possible to visualize an induction of PPM1D expression and this induction is maintained for up to 24h. The dose-response curve indicated a direct correlation between androgen concentration and PPM1D transcript levels. To confirm that the PPM1D induction by R1881 was due to the androgen receptor (AR) we treated LNCap with Casodex (AR inhibitor) in addition to R1881. This led to complete abrogation of PPM1D induction by androgen, showing that this regulation is dependent on active androgen receptor. Further studies are in progress to characterize whether the androgen receptor is able to bind to the PPM1D promoter and directly induce PPM1D expression, since we have already identified one androgen responsive element in the PPM1D promoter using the CONSITE software, suggesting a direct mechanism. We have also cloned the complete PPM1D cDNA and the specific shPPM1D aiming at functional analysis of PPM1D in prostate cell lines. Our results show that PPM1D is upregulated in more transformed, high grade prostate tumors and is induced by androgens, strongly suggesting its involvement in prostate tumor progression. Financial Support: CNPq, FAPESP, FINEP and PRP-USP

[Proc Amer Assoc Cancer Res, Volume 47, 2006]