The majority of human breast cancer is estrogen receptor alpha (ER) positive. While anti-estrogens/aromatase inhibitors are initially effective, resistance to these drugs commonly develops. Therapy-resistant tumors often retain ER signaling, via interaction with critical oncogenic coregulator proteins. To address these mechanisms of resistance, we have developed a novel ER coregulator binding modulator, ERX-11. ERX-11 interacts directly with ER and blocks the interaction between a subset of coregulators with both native and mutant forms of ER. ERX-11 effectively blocks ER-mediated oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant human breast cancer cells. ERX-11 is orally bioavailable, with no overt signs of toxicity and potent activity in both murine xenograft and patient-derived breast tumor explant models. This first-in-class agent, with its novel mechanism of action of disrupting critical protein-protein interactions, overcomes the limitations of current therapies and may be clinically translatable for patients with therapy-sensitive and therapy-resistant breast cancers.DOI: http://dx.doi.org/10.7554/eLife.26857.001

, glutamic acid-and leucine-rich protein-1 (PELP1) is a scaffolding oncogenic protein that functions as a coregulator for a number of nuclear receptors. p53 is an important transcription factor and tumor suppressor that has a critical role in DNA damage response (DDR) including cell cycle arrest, repair or apoptosis. In this study, we found an unexpected role for PELP1 in modulating p53-mediated DDR. PELP1 is phosphorylated at Serine1033 by various DDR kinases like ataxia-telangiectasia mutated, ataxia telangiectasia and Rad3-related or DNAPKc and this phosphorylation of PELP1 is important for p53 coactivation functions. PELP1-depleted p53 (wild-type) breast cancer cells were less sensitive to various genotoxic agents including etoposide, camptothecin or c-radiation. PELP1 interacts with p53, functions as p53-coactivator and is required for optimal activation of p53 target genes under genomic stress. Overall, these studies established a new role of PELP1 in DDRs and these findings will have future implications in our understanding of PELP1's role in cancer progression. Cell Death and Differentiation (2014) 21, 1409-1418; doi:10.1038/cdd.2014.55; published online 2 May 2014 p53 is considered as the guardian of genomic integrity and has an important role in initiating cellular response to various genomic stresses such as cell cycle arrest, senescence, DNA repair and apoptosis.1,2 Loss of p53 or mutations in p53 is observed in 450% of the cases of all cancers.3-5 Stabilization of p53 upon genomic stress and activation of its transcription functions are vital for its central role in the DNA damage/ genomic stress response and in its tumor-suppressive functions.6,7 Upon genomic stress, p53 is stabilized and activated because of a decreased interaction with its E3-ligase MDM2.8 Activated p53 then upregulates expression of target genes, such as p21/WAF1, GADD45, PUMA and NOXA, all of which are important in the cellular decisions for cell cycle arrest or apoptosis. Post-translational modifications of p53, including phosphorylation, acetylation, ubiquitinylation and methylation, 10-12 and interactions with several cofactors 13,14 have a critical role in the p53-mediated transcriptional response to the DNA damage response (DDR). Proline-, glutamic acid-and leucine-rich protein-1 (PELP1), a large multi-domain protein, modulates a number of biological processes and several pathways including estrogen signaling, and cancer progression. 17 It promotes cell proliferation by enhancing G1 to S phase progression via its interactions with the pRb/E2F pathway.25 PELP1 localizes to the nucleolus and has an important role in ribosomal biogenesis.26 PELP1 signaling is also implicated in apoptosis and differentiation, and PELP1 functions as a coactivator of RXR homodimers and RXR-PPAR heterodimers.27 Although PELP1's role in both cell proliferation and differentiation is evident, it is not known how PELP1 would affect p53-mediated DDR functions and whether PELP1 status would affect sensitivity to various genomic stresses.In this study,...

Triple-negative breast cancer (TNBC), the most aggressive breast cancer subtype, occurs in younger women and is associated with poor prognosis. Gain-of-function mutations in TP53 are a frequent occurrence in TNBC and have been demonstrated to repress apoptosis and up-regulate cell cycle progression. Even though TNBC responds to initial chemotherapy, resistance to chemotherapy develops and is a major clinical problem. Tumor recurrence eventually occurs and most patients die from their disease. An urgent need exists to identify molecular-targeted therapies that can enhance chemotherapy response. In the present study, we report that targeting PELP1, an oncogenic co-regulator molecule, could enhance the chemotherapeutic response of TNBC through the inhibition of cell cycle progression and activation of apoptosis. We demonstrate that PELP1 interacts with MTp53, regulates its recruitment, and alters epigenetic marks at the target gene promoters. PELP1 knockdown reduced MTp53 target gene expression, resulting in decreased cell survival and increased apoptosis upon genotoxic stress. Mechanistic studies revealed that PELP1 depletion contributes to increased stability of E2F1, a transcription factor that regulates both cell cycle and apoptosis in a context-dependent manner. Further, PELP1 regulates E2F1 stability in a KDM1A-dependent manner, and PELP1 phosphorylation at the S1033 residue plays an important role in mediating its oncogenic functions in TNBC cells. Accordingly, depletion of PELP1 increased the expression of E2F1 target genes and reduced TNBC cell survival in response to genotoxic agents. PELP1 phosphorylation was significantly greater in the TNBC tumors than in the other subtypes of breast cancer and in the normal tissues. These findings suggest that PELP1 is an important molecular target in TNBC, and that PELP1-targeted therapies may enhance response to chemotherapies.

Proline, Glutamic acid- and Leucine-rich Protein 1 (PELP1) is a proto-oncogene that modulates estrogen receptor (ER) signaling. PELP1 expression is upregulated in breast cancer, contributes to therapy resistance, and is a prognostic marker of poor survival. In a subset of breast tumors, PELP1 is predominantly localized in the cytoplasm and PELP1 participates in extranuclear signaling by facilitating ER interactions with Src and PI3 kinases. However, the mechanism by which PELP1 extranuclear actions contributes to cancer progression and therapy resistance remains unclear. In this study, we discovered that PELP1 crosstalked with the serine/threonine protein kinase mammalian target of rapamycin (mTOR) axis and modulated mTOR signaling. PELP1 knockdown significantly reduced the activation of mTOR downstream signaling components. Conversely, PELP1 overexpression excessively activated mTOR signaling components. We detected the presence of the mTOR signaling complex proteins in PELP1 immunoprecipitates. mTOR targeting drugs (Rapamycin or AZD8055) significantly reduced proliferation of PELP1 over expressed breast cancer cells both in vitro and in vivo xenograft tumor models. MCF7 cells that uniquely retain PELP1 in the cytoplasm showed resistance to hormonal therapy and mTOR inhibitors sensitized PELP1-cyto cells to hormonal therapy in xenograft assays. Notably, IHC studies using xenograft tumors derived from PELP1 overexpression model cells showed increased mTOR signaling and inhibition of mTOR rendered PELP1 driven tumors to be highly sensitive to therapeutic inhibition. Collectively, our data identified the PELP1-mTOR axis as a novel component of PELP1 oncogenic functions and suggest that mTOR inhibitor(s) will be effective chemotherapeutic agents for downregulating PELP1 oncogenic functions.

Most patients with estrogen receptor alpha-positive breast cancers (ER+ BC) initially respond to treatment but eventually develop therapy resistance with disease progression. Overexpression of oncogenic ER coregulators, including proline, glutamic acid, and leucine-rich protein 1 (PELP1), are implicated in BC progression. The lack of small molecules that inhibits PELP1 represents a major knowledge gap. Here, using a yeast-two-hybrid screen, we identified novel peptide inhibitors of PELP1 (PIPs). Biochemical assays demonstrated that one of these peptides, PIP1, directly interacted with PELP1 to block PELP1 oncogenic functions. Computational modeling of PIP1 revealed key residues contributing to its activity and facilitated the development of a small molecule inhibitor of PELP1, SMIP34, and further analyses confirmed that SMIP34 directly bound to PELP1. In BC cells, SMIP34 reduced cell growth in a PELP1-dependent manner. SMIP34 inhibited proliferation of not only wild-type (WT) but also mutant (MT) ER+ and therapy-resistant (TR) BC cells, in part by inducing PELP1 degradation via the proteasome pathway. RNA-seq analyses showed that SMIP34 treatment altered the expression of genes associated with estrogen response, cell cycle, and apoptosis pathways. In cell line-derived and patient-derived xenografts of both WT- and MT- ER+ BC models, SMIP34 reduced proliferation and significantly suppressed tumor progression. Collectively, these results demonstrate SMIP34 as a first-in-class inhibitor of oncogenic PELP1 signaling in advanced BC.

Background Glioblastoma (GBM) is a deadly neoplasm of the central nervous system. The molecular mechanisms and players that contribute to GBM development is incompletely understood. Methods The expression of PELP1 in different grades of glioma and normal brain tissues was analyzed using immunohistochemistry on a tumor tissue array. PELP1 expression in established and primary GBM cell lines was analyzed by Western blotting. The effect of PELP1 knockdown was studied using cell proliferation, colony formation, migration, and invasion assays. Mechanistic studies were conducted using RNA-seq, RT-qPCR, immunoprecipitation, reporter gene assays, and signaling analysis. Mouse orthotopic models were used for preclinical evaluation of PELP1 knock down. Results Nuclear receptor coregulator PELP1 is highly expressed in gliomas compared to normal brain tissues, with the highest expression in GBM. PELP1 expression was elevated in established and patient-derived GBM cell lines compared to normal astrocytes. Knockdown of PELP1 resulted in a significant decrease in cell viability, survival, migration, and invasion. Global RNA-sequencing studies demonstrated that PELP1 knockdown significantly reduced the expression of genes involved in the Wnt/β-catenin pathway. Mechanistic studies demonstrated that PELP1 interacts with and functions as a coactivator of β-catenin. Knockdown of PELP1 resulted in a significant increase in survival of mice implanted with U87 and GBM PDX models. Conclusions PELP1 expression is upregulated in GBM and PELP1 signaling via β-catenin axis contributes to GBM progression. Thus, PELP1 could be a potential target for the development of therapeutic intervention in GBM.

No abstract

Ovarian cancer (OC) is the deadliest of all gynecologic cancers in the United States. Despite success with initial chemotherapy, 70% of patients relapse with incurable disease. Development of chemotherapy resistance is the main factor for poor long-term survival in OC. OC stem cells are implicated in tumor initiation and therapy resistance and their elimination is critical for the development of efficient therapeutic strategies. The biological effects of estrogens are mediated through their cognate receptors: estrogen receptor alpha (ERα) and ER beta (ERβ). Emerging evidence suggests that OC cells express ERβ that functions as a tumor suppressor; however, the clinical utility of ERβ agonists in OC remains elusive. Here, we have tested the utility of ERβ to inhibit OC progression by employing ERβ specific agonists. We have used three different ERβ agonists: liquiritigenin (LIQ) isolated from the plant Glycyrrhiza uralensis, S-equol from soy isoflavone daidzein, and the synthetic compound LY500307 (Eli Lilly). Western analysis revealed detectable expression of ERβ in all OC models tested (SKOV3, BG1 and OVCAR3). Using ERβ reporter gene assay and ERβ specific target gene expression, we confirmed functionality of the ERβ pathway in OC cells. All three ERβ ligands showed significant growth inhibition in MTT and colony formation assays, and ERβ agonists promoted apoptosis. Treatment with ERβ agonists significantly upregulated the expression of ERβ via autocrine signaling. Mechanistic studies revealed ERβ mediated non-classical signaling via AP1 and SP1 as playing a critical role in ERβ mediated tumor suppression. Of the three ligands tested, LY500307 showed more potent growth inhibitory activity (IC50: 3μM). ERβ knockdown using shRNA significantly reduced the ERβ agonist mediated growth inhibition. Interestingly, we found that OC stem cells express ERβ and ERβ agonists significantly decrease the sphere formation by OC stem cells. Additional assays revealed that ERβ agonists reduced the stemness of OC stem cells and enhanced their sensitivity to chemotherapy. Accordingly, ERβ agonists significantly reduced the growth of chemotherapy resistant ovarian cancer model cells (cisplatin-resistant ES2, paclitaxel resistant SKOV-3TR cells) and sensitized them to apoptosis. Collectively, our findings show that ERβ agonists have the potential to significantly inhibit ovarian cancer cell growth and reduce stemness; therefore, ERβ agonists represent novel therapeutic agents for the management of ovarian cancer. Citation Format: Gangadhara Reddy Sareddy, Javier E. Chavez, Humberto Salazar, Monica Mann, Jocelyn Hernandez, Samaya Rajeshwari Krishnan, Edward Kost, Rajeshwar Rao Tekmal, Ratna K. Vadlamudi. Therapeutic efficacy of ERβ agonists on ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 606. doi:10.1158/1538-7445.AM2014-606