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Re: Epigenetic Regulation of Phosphatidylinositol 3,4,5-Triphosphate-Dependent Rac Exchanger 1 Gene Expression in Prostate Cancer Cells
Urological Survey
Uro-Science Re: Epigenetic Regulation of Phosphatidylinositol 3,4,5-Triphosphate-Dependent Rac Exchanger 1 Gene Expression in Prostate Cancer Cells C. Y. Wong, H. Wuriyanghan, Y. Xie, M. F. Lin, P. W. Abel and Y. Tu Department of Pharmacology, Creighton University School of Medicine, Omaha, Nebraska J Biol Chem 2011; 286: 25813–25822.
Aberrant up-regulation of P-Rex1 expression plays important roles in cancer progression and metastasis. The present study investigated the regulatory mechanism underlying P-Rex1 gene expression in prostate cancer cells. We showed that P-Rex1 expression was much higher in metastatic prostate cancer cells than in prostate epithelial cells and non-metastatic prostate cancer cells. Histone deacetylase (HDAC) inhibitors or silence of endogenous HDAC1 and HDAC2 markedly elevated P-Rex1 transcription in non-metastatic prostate cancer cells, whereas overexpression of recombinant HDAC1 in metastatic prostate cancer cells suppressed P-Rex1 expression. HDAC inhibitor trichostatin A (TSA) also significantly increased P-Rex1 promoter activity and caused acetylated histones to accumulate and associate with the P-Rex1 promoter. One Sp1 site, essential for basal promoter activity, was identified as critical for the TSA effect. TSA treatment did not alter the DNA-binding activity of Sp1 toward the P-Rex1 promoter; however, it facilitated the dissociation of the repressive HDAC1 and HDAC2 from the Sp1 binding region. Interestingly, HDAC1 association with Sp1 and with the P-Rex1 promoter were much weaker in metastatic prostate cancer PC-3 cells than in non-metastatic prostate cancer cells, and HDAC inhibitors only had very modest stimulatory effects on P-Rex1 promoter activity and P-Rex1 expression in PC-3 cells. Altogether, our studies demonstrate that HDACs could regulate P-Rex1 gene transcription by interaction with Sp1 and by region-specific changes in histone acetylation within the P-Rex1 promoter. Disassociation of HDACs from Sp1 on the P-Rex1 promoter may contribute to aberrant up-regulation of P-Rex1 in cancer. Editorial Comment: Rac is a member of the Rho family of small G-proteins, which are important regulators of the cell cytoskeleton during the establishment of cell polarity and cell processes such as migration, vesicle trafficking and cell division. Hyperactivation of Rac has been found in some cancers and may control tumor cell movement. P-Rex13 is a guanine nucleotide exchange factor that specifically activates Rac by catalyzing exchange of GDP for GTP bound to Rac. P-Rex1 simultaneously integrates signals from several input pathways and has an important role in normal physiology and pathological conditions. The expression levels of P-Rex1 are low in normal human primary prostate epithelial cells and in nonmetastatic prostate cancer cells but are highly elevated in metastatic prostate cancer cells, suggesting that P-Rex1 expression levels are an index of metastasis. Upregulated P-Rex1 could be a novel therapeutic target in prostate cancer. Understanding fundamental mechanisms controlling expression of P-Rex1 is crucial for introducing effective therapies. However, the exact molecular mechanism of P-Rex1 regulation is entirely unknown. The authors have identified the P-Rex1 gene promoter as a target for regulatory repression of P-Rex1 gene transcription by an Sp1-HDAC complex. P-Rex1 was postulated to function as a molecule that simultaneously integrates signals from several input pathways as the cells rearrange their cytoskeleton and migrate in response to those signals. The 0022-5347/12/1873-1127/0 THE JOURNAL OF UROLOGY® © 2012 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
AND
RESEARCH, INC.
Vol. 187, 1127-1129, March 2012 Printed in U.S.A. DOI:10.1016/j.juro.2011.11.022
www.jurology.com
1127
1128
URO-SCIENCE
finding that P-Rex1 gene expression is subject to HDAC mediated regulation extends the understanding of the essential role of P-Rex1 in physiological and pathological situations. Also, the data suggest that disassociation of HDACs from Sp1 on the P-Rex1 promoter may contribute to aberrant up-regulation of P-Rex1 in metastatic prostate cancer. Anthony Atala, M.D.
Re: Targeting the Regulation of Androgen Receptor Signaling by the Heat Shock Protein 90 Cochaperone FKBP52 in Prostate Cancer Cells J. T. De Leon, A. Iwai, C. Feau, Y. Garcia, H. A. Balsiger, C. L. Storer, R. M. Suro, K. M. Garza, S. Lee, Y. S. Kim, Y. Chen, Y. M. Ning, D. L. Riggs, R. J. Fletterick, R. K. Guy, J. B. Trepel, L. M. Neckers and M. B. Cox Department of Biological Sciences and Border Biomedical Research Center, University of Texas at El Paso, El Paso, Texas Proc Natl Acad Sci U S A 2011; 108: 11878 –11883.
Drugs that target novel surfaces on the androgen receptor (AR) and/or novel AR regulatory mechanisms are promising alternatives for the treatment of castrate-resistant prostate cancer. The 52 kDa FK506 binding protein (FKBP52) is an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We used a modified receptor-mediated reporter assay in yeast to screen a diversified natural compound library for inhibitors of FKBP52-enhanced AR function. The lead compound, termed MJC13, inhibits AR function by preventing hormone-dependent dissociation of the Hsp90-FKBP52-AR complex, which results in less hormone-bound receptor in the nucleus. Assays in early and late stage human prostate cancer cells demonstrated that MJC13 inhibits AR-dependent gene expression and androgen-stimulated prostate cancer cell proliferation. Editorial Comment: Androgens are a major stimulator of prostate tumor growth, and all current therapies act as classic antagonists by competing with androgens for binding the androgen receptor hormone binding pocket. This mechanism of action exploits the dependence of androgen receptors on hormone activation. However, current treatment options become ineffective in castrate resistant prostate cancer, although castrate resistant prostate cancer remains ligand/androgen receptor dependent. Drugs that target novel surfaces on the androgen receptor and/or novel androgen receptor regulatory mechanisms may provide promising alternatives for the treatment of castrate resistant prostate cancer. The authors identified a surface region on the androgen receptor ligand binding domain that, when mutated, results in a greater functional dependence on FKBP52. This motif overlaps with the recently characterized BF3 surface. The authors developed a series of small molecules that inhibit FKBP52 regulation of androgen receptor function. These agents are predicted to act via binding to the BF3 surface in the androgen receptor ligand binding domain. The most promising compound, MJC13, inhibits hormone induced androgen receptor chaperone complex dissociation and nuclear translocation, and effectively blocks androgen receptor dependent gene expression in cellular models of prostate cancer. Further studies are needed to characterize the MJC13 binding site, improve compound efficacy and improve receptor specificity. MJC13 is a novel example of an inhibitor that specifically targets the regulation of steroid hormone receptor function by an Hsp90 associated co-chaperone and thus serves as an excellent starting point for development of FKBP52 specific inhibitors to treat hormone dependent diseases. Anthony Atala, M.D.
Uro-Science Re: Epigenetic Regulation of Phosphatidylinositol 3,4,5-Triphosphate-Dependent Rac Exchanger 1 Gene Expression in Prostate Cancer Cells C. Y. Wong, H. Wuriyanghan, Y. Xie, M. F. Lin, P. W. Abel and Y. Tu Department of Pharmacology, Creighton University School of Medicine, Omaha, Nebraska J Biol Chem 2011; 286: 25813–25822.
Aberrant up-regulation of P-Rex1 expression plays important roles in cancer progression and metastasis. The present study investigated the regulatory mechanism underlying P-Rex1 gene expression in prostate cancer cells. We showed that P-Rex1 expression was much higher in metastatic prostate cancer cells than in prostate epithelial cells and non-metastatic prostate cancer cells. Histone deacetylase (HDAC) inhibitors or silence of endogenous HDAC1 and HDAC2 markedly elevated P-Rex1 transcription in non-metastatic prostate cancer cells, whereas overexpression of recombinant HDAC1 in metastatic prostate cancer cells suppressed P-Rex1 expression. HDAC inhibitor trichostatin A (TSA) also significantly increased P-Rex1 promoter activity and caused acetylated histones to accumulate and associate with the P-Rex1 promoter. One Sp1 site, essential for basal promoter activity, was identified as critical for the TSA effect. TSA treatment did not alter the DNA-binding activity of Sp1 toward the P-Rex1 promoter; however, it facilitated the dissociation of the repressive HDAC1 and HDAC2 from the Sp1 binding region. Interestingly, HDAC1 association with Sp1 and with the P-Rex1 promoter were much weaker in metastatic prostate cancer PC-3 cells than in non-metastatic prostate cancer cells, and HDAC inhibitors only had very modest stimulatory effects on P-Rex1 promoter activity and P-Rex1 expression in PC-3 cells. Altogether, our studies demonstrate that HDACs could regulate P-Rex1 gene transcription by interaction with Sp1 and by region-specific changes in histone acetylation within the P-Rex1 promoter. Disassociation of HDACs from Sp1 on the P-Rex1 promoter may contribute to aberrant up-regulation of P-Rex1 in cancer. Editorial Comment: Rac is a member of the Rho family of small G-proteins, which are important regulators of the cell cytoskeleton during the establishment of cell polarity and cell processes such as migration, vesicle trafficking and cell division. Hyperactivation of Rac has been found in some cancers and may control tumor cell movement. P-Rex13 is a guanine nucleotide exchange factor that specifically activates Rac by catalyzing exchange of GDP for GTP bound to Rac. P-Rex1 simultaneously integrates signals from several input pathways and has an important role in normal physiology and pathological conditions. The expression levels of P-Rex1 are low in normal human primary prostate epithelial cells and in nonmetastatic prostate cancer cells but are highly elevated in metastatic prostate cancer cells, suggesting that P-Rex1 expression levels are an index of metastasis. Upregulated P-Rex1 could be a novel therapeutic target in prostate cancer. Understanding fundamental mechanisms controlling expression of P-Rex1 is crucial for introducing effective therapies. However, the exact molecular mechanism of P-Rex1 regulation is entirely unknown. The authors have identified the P-Rex1 gene promoter as a target for regulatory repression of P-Rex1 gene transcription by an Sp1-HDAC complex. P-Rex1 was postulated to function as a molecule that simultaneously integrates signals from several input pathways as the cells rearrange their cytoskeleton and migrate in response to those signals. The 0022-5347/12/1873-1127/0 THE JOURNAL OF UROLOGY® © 2012 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
AND
RESEARCH, INC.
Vol. 187, 1127-1129, March 2012 Printed in U.S.A. DOI:10.1016/j.juro.2011.11.022
www.jurology.com
1127
1128
URO-SCIENCE
finding that P-Rex1 gene expression is subject to HDAC mediated regulation extends the understanding of the essential role of P-Rex1 in physiological and pathological situations. Also, the data suggest that disassociation of HDACs from Sp1 on the P-Rex1 promoter may contribute to aberrant up-regulation of P-Rex1 in metastatic prostate cancer. Anthony Atala, M.D.
Re: Targeting the Regulation of Androgen Receptor Signaling by the Heat Shock Protein 90 Cochaperone FKBP52 in Prostate Cancer Cells J. T. De Leon, A. Iwai, C. Feau, Y. Garcia, H. A. Balsiger, C. L. Storer, R. M. Suro, K. M. Garza, S. Lee, Y. S. Kim, Y. Chen, Y. M. Ning, D. L. Riggs, R. J. Fletterick, R. K. Guy, J. B. Trepel, L. M. Neckers and M. B. Cox Department of Biological Sciences and Border Biomedical Research Center, University of Texas at El Paso, El Paso, Texas Proc Natl Acad Sci U S A 2011; 108: 11878 –11883.
Drugs that target novel surfaces on the androgen receptor (AR) and/or novel AR regulatory mechanisms are promising alternatives for the treatment of castrate-resistant prostate cancer. The 52 kDa FK506 binding protein (FKBP52) is an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We used a modified receptor-mediated reporter assay in yeast to screen a diversified natural compound library for inhibitors of FKBP52-enhanced AR function. The lead compound, termed MJC13, inhibits AR function by preventing hormone-dependent dissociation of the Hsp90-FKBP52-AR complex, which results in less hormone-bound receptor in the nucleus. Assays in early and late stage human prostate cancer cells demonstrated that MJC13 inhibits AR-dependent gene expression and androgen-stimulated prostate cancer cell proliferation. Editorial Comment: Androgens are a major stimulator of prostate tumor growth, and all current therapies act as classic antagonists by competing with androgens for binding the androgen receptor hormone binding pocket. This mechanism of action exploits the dependence of androgen receptors on hormone activation. However, current treatment options become ineffective in castrate resistant prostate cancer, although castrate resistant prostate cancer remains ligand/androgen receptor dependent. Drugs that target novel surfaces on the androgen receptor and/or novel androgen receptor regulatory mechanisms may provide promising alternatives for the treatment of castrate resistant prostate cancer. The authors identified a surface region on the androgen receptor ligand binding domain that, when mutated, results in a greater functional dependence on FKBP52. This motif overlaps with the recently characterized BF3 surface. The authors developed a series of small molecules that inhibit FKBP52 regulation of androgen receptor function. These agents are predicted to act via binding to the BF3 surface in the androgen receptor ligand binding domain. The most promising compound, MJC13, inhibits hormone induced androgen receptor chaperone complex dissociation and nuclear translocation, and effectively blocks androgen receptor dependent gene expression in cellular models of prostate cancer. Further studies are needed to characterize the MJC13 binding site, improve compound efficacy and improve receptor specificity. MJC13 is a novel example of an inhibitor that specifically targets the regulation of steroid hormone receptor function by an Hsp90 associated co-chaperone and thus serves as an excellent starting point for development of FKBP52 specific inhibitors to treat hormone dependent diseases. Anthony Atala, M.D.