normal prostate tissue, and further decreased in lymphatic metastasis. This evidence indicates that protein 4.1B may act as a prostate tumorprogression suppressor as well as a negative regulator of malignancy across a spectrum of tumor types. Protein 4.1B may provide new aidin cancer diagnosis, as well as to be a novel target in treatment development.

doi:10.1016/j.urolonc.2007.11.024Yingming Li, M.D., Kenneth S. Koeneman, M.D.

The zinc finger protein Ras-responsive element binding protein-1 is a coregulator of the androgen receptor: Implications for the roleof the Ras pathway in enhancing androgenic signaling in prostate cancer. Mukhopadhyay NK, Cinar B, Mukhopadhyay L, LutchmanM, Ferdinand AS, Kim J, Chung LW, Adam RM, Ray SK, Leiter AB, Richie JP, Liu BC, Freeman MR, Department of Urology/Surgery,Children’s Hospital Boston, Harvard Medical School, Boston, MA.

Mol Endocrinol 2007;21:2056–70

Androgen receptor (AR) plays an important role in normal prostate function as well as in the etiology of prostate cancer. Activation ofAR is dictated by hormone binding and by interactions with co-regulators. Several of these co-regulators are known targets of Ras-relatedsignals. Recent evidence suggests that Ras activation may play a causal role in the progression of prostate cancer toward a more malignantand hormone-insensitive phenotype. In the present study, we used a transcription factor–transcription factor interaction array method toidentify the zinc finger protein Ras-responsive element binding protein (RREB-1) as a partner and coregulator of AR. In LNCaP prostatecancer cells, RREB-1 was found to be present in a complex with endogenous AR as determined by coimmunoprecipitation, glutathioneS-transferase pull down, and immunofluorescence analyses. RREB-1 bound to the prostate-specific antigen (PSA) promoter as assessed bychromatin immunoprecipitation. Transient expression of RREB-1 down-regulated AR-mediated promoter activity and suppressed expres-sion of PSA protein. The repressor activity of RREB-1 was significantly attenuated by cotransfection of activated Ras. Moreover, expressionof the dominant-negative N-17-Ras or, alternatively, use of the MAPK kinase inhibitor PD98059 [2-(2-amino-3-methyoxyphenyl)-4H-1-benzopyran-4-one] abolished the effect of Ras in attenuating RREB-1-mediated repression. Furthermore, inhibition of RREB-1 expressionby RNA interference enhanced the effect of Ras on PSA promoter activity and PSA expression. In addition, activation of the Ras pathwaydepleted AR from the RREB-1/AR complex. Collectively, our data for the first time identify RREB-1 as a repressor of AR and furtherimplicate the Ras/MAPK kinase pathway as a likely antagonist of the inhibitory effects of RREB-1 on androgenic signaling.

Commentary

RREB-1 protein was originally identified as a protein that binds to the upstream Ras responsive element of human calcitonin promoter,and activates transcription in the presence of Ras. Recently, RREB-1has been reported to down-regulate p16INK4a promoter and the humanangiotensinogen gene. In this paper, Mukhopadhyay et al. used the new technology named “transcription factor-transcription factor (TF-TF)interaction array” to identify RREB-1 protein as a novel AR coregulator, serving as potent AR co-repressor to repress PSA gene expression.The repressor activity of RREB-1 was significantly decreased by RAS activation. The RAS/MAPK kinase pathway can overcome ARrepression by its corepressor RREB-1. This paper provides novel information on AR and its target gene regulation. The pathway describedclinically could be involved in the prostate cancer progression, since low levels of androgen are still present in relapsed, “androgenrefractory” prostate cancer.

doi:10.1016/j.urolonc.2007.11.025Yingming Li, M.D., Kenneth S. Koeneman, M.D.

SOX9 is expressed in normal prostate basal cells and regulates androgen receptor expression in prostate cancer cells. Wang H,McKnight NC, Zhang T, Lu ML, Balk SP, Yuan X, Cancer Biology Program, Division of Hematology/Oncology, Department of Medicine,Beth Israel Deaconess Medical Center, Urology Research Laboratory, Brigham and Women’s Hospital and Harvard Medical School,Boston, MA.

Cancer Res 2007;67:528–36

SOX9 is a member of the SOX [Sry-related high-mobility group (HMG) box] family of HMG DNA-binding domain transcription factorsand is required for the development and differentiation of multiple cell lineages. This report shows that basal epithelial cells express SOX9in normal prostate, with no detectable expression in luminal epithelial cells. In contrast, SOX9 is expressed in primary prostate cancersin vivo, at a higher frequency in recurrent prostate cancer and in prostate cancer cell lines (LNCaP, CWR22, PC3, and DU145). SOX9message and protein levels in prostate cancer cells were increased by treatment with glycogen synthase kinase 3� inhibitor (SB415286), andSOX9 was reduced when �-catenin was down-regulated by small interfering RNA (siRNA), indicating that SOX9 expression in prostatecancer is regulated by Wnt/�-catenin signaling. SOX9 bound specifically to androgen receptor (AR) DNA-binding domain glutathioneS-transferase fusion proteins, and this interaction was dependent on a short peptide immediately COOH-terminal to the DNA-bindingdomain (the C-terminal extension), which is required for interactions between steroid hormone receptors and the architectural HMG

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proteins. Exogenous SOX9 expressed at high nonphysiologic levels decreased AR expression and activity; however, at lower levels, SOX9increased AR protein expression. Significantly, down-regulation of SOX9 by siRNA in prostate cancer cells reduced endogenous AR proteinlevels and cell growth, indicating that SOX9 contributes to AR regulation and decreased cellular proliferation. These results indicate thatSOX9 in prostate basal cells supports the development and maintenance of the luminal epithelium and that a subset of prostate cancer cellsmay escape basal cell requirements through SOX9 expression.

Commentary

Normal prostate contains luminal and basal cells, which are quite phenotypically different. Luminal cells are androgen receptor (AR) positive,androgen-dependent, secrete PSA, and do not proliferate. Basal cells are androgen receptor negative, androgen-independent, do not secrete PSA,and are capable of regenerating and proliferating. Stem cells may likely be classified more as a basal cell phenotype. Cancerous cells, through“de-differentiation” (as re-expression) of development genes, can resemble stem cells, and express stem cell markers. In this article, the authorsreported a member of the SOX family of HMG DNA binding domain transcription factors is expressed in the basal layer of normal human adultprostate, but not in luminal cells. Interestingly, 12 out of 29 (41.4%) primary prostate cancer samples, and 35 out of 39 (89.7%) recurrent localprostate cancer tissue specimens from radical prostatectomies were stained SOX9 positive. Serial prostate cancer cell lines were examined (positiveof SOX9), including PC3, LNCap, C4-2, CWR22R3, and CWR22Rv1. The expression of SOX9 is modulated by Wnt/b-catenin signaling and thePI3/Akt pathway, which appears to be an important pathway for stem cell maintenance. SOX9 was also found to interact directly to AR by bindingto its DNA binding domain. SOX9 positively regulates AR expression in prostate cells, and thus affects PSA expression. The regulation of ARseems to be a translational or post-translational event. Finally, down-regulation of SOX9 inhibits the prostate cancer cell proliferation. Theexpression of SOX9 may be linked to cancer grade and prognosis. SOX9 regulated genes may similarly play an important role in supportingprostate cancer growth independent of basal cells. Shutting down SOX9 expression may theoretically be a new target for therapy.

doi:10.1016/j.urolonc.2007.11.026Yingming Li, M.D., Kenneth S. Koeneman, M.D.

Mitogenic action of the androgen receptor sensitizes prostate cancer cells to taxane-based cytotoxic insult. Hess-Wilson JK, Daly HK,Zagorski WA, Montville CP, Knudsen KE, Department of Cell Biology, University of Cincinnati College of Medicine, Cincinnati, OH.

Cancer Res 2006;66:11998–2008

Prostate cancer cells are dependent on androgen for growth and survival; as such, inhibition of androgen receptor (AR) activity is the first lineof intervention for disseminated disease. Recently, specific cytotoxic agents have been shown to extend survival times in patients with advanceddisease. Given the established ability of androgen to modify cell survival in prostate cancer cells, it is imperative to determine the effect of thehormonal environment on cytotoxic response. Here, we show that the response of prostate cancer cells to taxane-induced cell death is significantlyenhanced by androgen stimulation in AR-positive, androgen-dependent prostate cancer cells. Similar results were observed on androgen-independent AR activation. By contrast, AR-positive yet androgen-independent or AR-negative cells were refractory to androgen influence ontaxane function. The ability of androgen to potentiate taxane activity was dependent on its mitogenic capacity and was separable from overall ARactivity, as co-administration of AR antagonists, G(1) cyclin-dependent kinase inhibitors, or high-dose (growth inhibitory) androgen nullified theproapoptotic function of androgen. Observed induction of cell death was attributed to caspase-dependent apoptosis and correlated with p53activation. Combined, these data indicate that the cytotoxic effects of taxanes are substantially influenced by the hormonal environment and/orstatus of AR activity in prostate cancer cells and provide the foundation for refinement and optimization of cytotoxic intervention in prostate cancer.

Commentary

Taxane class antineoplastic drugs (palitaxol and docetaxol) are used as adjuvant therapy in treating androgen-independent prostate cancer.The effect of this current sequential and combination regime on overall survival and tumor volume in xenograft models has recently beenassessed in several preclinical studies, and has led to divergent conclusions about androgen action. Does the administration of taxane andandrogen ablation concurrently reach the highest efficiency, or should the taxane drug be administered before castration, which would bea currently clinically nonstandard dosing.

In androgen-dependent cells, the presence of androgen sensitizes the cell death induced by taxane. The sensitization only exists at themitogenic concentration of androgen that induces cell proliferation. The cell death exquisitely depends on the mitogenic capacity of AR;the enhancement of the taxane drug’s action by AR is through facilitating cell cycle progression. Clinically, this may be a “moot” point,but worth knowing. In androgen-independent cells, androgen administration did not facilitate taxane’s cytotoxicity. This article has providedthe understanding of the relation between androgen, AR, and taxane, and renews reformulation about the way and timing to employandrogen ablation and taxane type drugs to treat both androgen-dependent, and -independent prostate cancer effectively.

doi:10.1016/j.urolonc.2007.11.027Yingming Li, M.D., Kenneth S. Koeneman, M.D.

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