Prostate Cancer (PCa), an androgen-dependent tumor, is highly sensitive to perturbation of intratumoral steroid biosynthesis and metabolism of exogenous ligands: androgens but also estrogens and their metabolites. The complexity of PCa pathophysiology is enhanced by other signaling molecules such as nitric oxide (NO) and oxygen. A novel and pivotal function of ER? and endothelial NO Synthase (eNOS) in the acquisition of an aggressive PCa phenotype has been identified by our group. Specifically, we demonstrated that activation of the ER?/eNOS pathway is crucial for tumor progression within the prostate microenvironment, highly sensitive to local changes in hormonal levels and oxygen tension. We recently identified in PCa a transcriptional prognostic signature comprising a significant number of genes up-regulated in patients with worse clinical outcome. Transcriptional induction was due to chromatin remodeling mediated by a combinatorial complex between ER? and eNOS. In the same patients, other prognostic genes, among which the Glutathione Transferase GSTP1, were downregulated. In PCa, silencing of GSTP1 is frequently caused by promoter hypermethylation, a common early event in prostate carcinogenesis. Here we first validated loss of GSTP1 in vivo, in Tissue Micro Arrays from a retrospective cohort of patients (n.88), and correlated it with decreased disease-specific survival. Further, we show that the ER?/eNOS complex plays a role in GSTP1 transcriptional repression by being recruited at ERE sites in the gene promoter with consequential remodeling of the local chromatin. Treatment with ER? antagonist or its natural ligand ??-Adiol and/or with eNOS inhibitors abrogated the binding and reversed GSTP1 silencing. Similar results were obtained by using genetic approaches, i. siRNA-mediated ER??interference and ii. overexpression a dominant negative eNOS, confirming the crucial role of the ER?/eNOS complex in GSTP1 repression. Of interest, in PCa cultured cells from patients with worse outcome, silencing by ER?/eNOS appeared to be the sole mechanism regulating GSTP1 expression. More importantly, in vivo ChIP assays, using fresh surgical tissues explanted from PCa patients, revealed that this mechanism can coexist with promoter hypermethylation. These results led us to postulate that in PCa the repressive function exerted by the ER??eNOS complex may be an epigenetic event favoring inactivation of the GSTP1 locus and represent an alternative or reinforcing mechanism to DNA methylation.
Silencing of prostate cancer prognostic genes by ERb/eNOS complex: downregulation of GSTP1
A Aiello;A Farsetti
2011
Abstract
Prostate Cancer (PCa), an androgen-dependent tumor, is highly sensitive to perturbation of intratumoral steroid biosynthesis and metabolism of exogenous ligands: androgens but also estrogens and their metabolites. The complexity of PCa pathophysiology is enhanced by other signaling molecules such as nitric oxide (NO) and oxygen. A novel and pivotal function of ER? and endothelial NO Synthase (eNOS) in the acquisition of an aggressive PCa phenotype has been identified by our group. Specifically, we demonstrated that activation of the ER?/eNOS pathway is crucial for tumor progression within the prostate microenvironment, highly sensitive to local changes in hormonal levels and oxygen tension. We recently identified in PCa a transcriptional prognostic signature comprising a significant number of genes up-regulated in patients with worse clinical outcome. Transcriptional induction was due to chromatin remodeling mediated by a combinatorial complex between ER? and eNOS. In the same patients, other prognostic genes, among which the Glutathione Transferase GSTP1, were downregulated. In PCa, silencing of GSTP1 is frequently caused by promoter hypermethylation, a common early event in prostate carcinogenesis. Here we first validated loss of GSTP1 in vivo, in Tissue Micro Arrays from a retrospective cohort of patients (n.88), and correlated it with decreased disease-specific survival. Further, we show that the ER?/eNOS complex plays a role in GSTP1 transcriptional repression by being recruited at ERE sites in the gene promoter with consequential remodeling of the local chromatin. Treatment with ER? antagonist or its natural ligand ??-Adiol and/or with eNOS inhibitors abrogated the binding and reversed GSTP1 silencing. Similar results were obtained by using genetic approaches, i. siRNA-mediated ER??interference and ii. overexpression a dominant negative eNOS, confirming the crucial role of the ER?/eNOS complex in GSTP1 repression. Of interest, in PCa cultured cells from patients with worse outcome, silencing by ER?/eNOS appeared to be the sole mechanism regulating GSTP1 expression. More importantly, in vivo ChIP assays, using fresh surgical tissues explanted from PCa patients, revealed that this mechanism can coexist with promoter hypermethylation. These results led us to postulate that in PCa the repressive function exerted by the ER??eNOS complex may be an epigenetic event favoring inactivation of the GSTP1 locus and represent an alternative or reinforcing mechanism to DNA methylation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
