MNAR functionally interacts with both NH2- and COOH-terminal GR domains to modulate transactivation

Cryo-EM reveals the architecture of the PELP1-WDR18 molecular scaffold

PELP1 (Proline-, Glutamic acid-, Leucine-rich protein 1) is a large scaffolding protein that functions in many cellular pathways including steroid receptor (SR) coactivation, heterochromatin maintenance, and ribosome biogenesis. PELP1 is a proto-oncogene whose expression is upregulated in many human cancers, but how the PELP1 scaffold coordinates its diverse cellular functions is poorly understood. Here we show that PELP1 serves as the central scaffold for the human Rix1 complex whose members include WDR18, TEX10, and SENP3. We reconstitute the mammalian Rix1 complex and identified a stable sub-complex comprised of the conserved PELP1 Rix1 domain and WDR18. We determine a 2.7 Å cryo-EM structure of the subcomplex revealing an interconnected tetrameric assembly and the architecture of PELP1's signaling motifs, including eleven LxxLL motifs previously implicated in SR signaling and coactivation of Estrogen Receptor alpha (ERα) mediated transcription. However, the structure shows that none of these motifs is in a conformation that would support SR binding. Together this work establishes that PELP1 scaffolds the Rix1 complex, and association with WDR18 may direct PELP1's activity away from SR coactivation.

90 YEARS OF PROGESTERONE: Steroid receptors as MAPK signaling sensors in breast cancer: let the fates decide

Steroid hormone receptors (SRs) are classically defined as ligand-activated transcription factors that function as master regulators of gene programs important for a wide range of processes governing adult physiology, development, and cell or tissue homeostasis. A second function of SRs includes the ability to activate cytoplasmic signaling pathways. Estrogen (ER), androgen (AR), and progesterone (PR) receptors bind directly to membrane-associated signaling molecules including mitogenic protein kinases (i.e. c-SRC and AKT), G-proteins, and ion channels to mediate context-dependent actions via rapid activation of downstream signaling pathways. In addition to making direct contact with diverse signaling molecules, SRs are further fully integrated with signaling pathways by virtue of their N-terminal phosphorylation sites that act as regulatory hot-spots capable of sensing the signaling milieu. In particular, ER, AR, PR, and closely related glucocorticoid receptors (GR) share the property of accepting (i.e. sensing) ligand-independent phosphorylation events by proline-directed kinases in the MAPK and CDK families. These signaling inputs act as a 'second ligand' that dramatically impacts cell fate. In the face of drugs that reliably target SR ligand-binding domains to block uncontrolled cancer growth, ligand-independent post-translational modifications guide changes in cell fate that confer increased survival, EMT, migration/invasion, stemness properties, and therapy resistance of non-proliferating SR+ cancer cell subpopulations. The focus of this review is on MAPK pathways in the regulation of SR+ cancer cell fate. MAPK-dependent phosphorylation of PR (Ser294) and GR (Ser134) will primarily be discussed in light of the need to target changes in breast cancer cell fate as part of modernized combination therapies.

PELP1 is a novel oncogene in gastric tumorigenesis and negatively regulated by miR-15 family microRNAs

BACKGROUD

Gastric cancer (GC) is one of the leading causes of cancer-related death in East Asia and some South American countries, but its mechanism has not been clarified clearly. Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1), a co-regulatory molecule of estrogen receptor α (ER α), is up-regulated in series of cancers such as endometrial carcinoma, ovarian cancer, colorectal cancer, breast cancer, and non-small cell lung cancer. However, PELP1's role in GC is still obscure, and its aberrant expression in cancers also remains to be explained.

METHODS

Immunohistochemical staining and Real-time PCR were used to compare the expression level of PELP1 in GC tissues and adjacent tissues. Western blot was used to detect the expression of PELP1 in cell lines. Kaplan-meier analysis and chi-square test were applied to evaluate the potential of PELP1 to function as a cancer biomarker. RNA interference was used to inhibit PELP1 expression in GC cells, followed by detecting cell proliferation, apoptosis, migration and invasion. Luciferase assay was conducted to validate whether miR-15 family members can directly target PELP1.

RESULTS

In this study, we validated that PELP1 was significantly up-regulated in GC samples and cell lines. It was also demonstrated that the up-regulation of PELP1 was associated with several clinicopathologic features such as tumor diameter (P< 0.001), serum CEA level (P= 0.034), and lymphatic metastasis (P= 0.0009) of GC patients, and its high expression was correlated with shorter disease-free survival and overall survival of the patients. Knockdown of PELP1 remarkably arrested the proliferationï¼ migration and invasion, while promoted apoptosis. We also confirmed that miR-15 family microRNAs, most of which were down-regulated and tumor suppressor in cancers, were posttranscriptional regulators of PELP1.

CONCLUSION

In conclusion, we demonstrated that PELP1 was an oncogene of GC associated with patients' prognosis and miR-15 family members contributed to its aberrant expression in cancers.

PELP1: a key mediator of oestrogen signalling and actions in the brain

Proline-, glutamic acid- and leucine-rich protein 1 (PELP1) is an oestrogen receptor (ER) coregulator protein identified by our collaborative group. Work from our laboratory and others has shown that PELP1 is a scaffold protein that interacts with ERs and kinase signalling factors, as well as proteins involved in chromatin remodelling and DNA repair. Its role in mediating 17β-oestradiol (E₂ ) signalling and actions has been studied in detail in cancer cells, although only recently has attention turned to its role in the brain. In this review, we discuss the tissue, cellular and subcellular localisation of PELP1 in the brain. We also discuss recent evidence from PELP1 forebrain-specific knockout mice demonstrating a critical role of PELP1 in mediating both extranuclear and nuclear ER signalling in the brain, as well as E₂ -induced neuroprotection, anti-inflammatory effects and regulation of cognitive function. Finally, the PELP1 interactome and unique gene network regulated by PELP1 in the brain is discussed, especially because it provides new insights into PELP1 biology, protein interactions and mechanisms of action in the brain. As a whole, the findings discussed in the present review indicate that PELP1 functions as a critical ER coregulator in the brain to mediate E₂ signalling and actions.

Glucocorticoids promote Von Hippel Lindau degradation and Hif-1α stabilization

Glucocorticoid (GC) and hypoxic transcriptional responses play a central role in tissue homeostasis and regulate the cellular response to stress and inflammation, highlighting the potential for cross-talk between these two signaling pathways. We present results from an unbiased in vivo chemical screen in zebrafish that identifies GCs as activators of hypoxia-inducible factors (HIFs) in the liver. GCs activated consensus hypoxia response element (HRE) reporters in a glucocorticoid receptor (GR)-dependent manner. Importantly, GCs activated HIF transcriptional responses in a zebrafish mutant line harboring a point mutation in the GR DNA-binding domain, suggesting a nontranscriptional route for GR to activate HIF signaling. We noted that GCs increase the transcription of several key regulators of glucose metabolism that contain HREs, suggesting a role for GC/HIF cross-talk in regulating glucose homeostasis. Importantly, we show that GCs stabilize HIF protein in intact human liver tissue and isolated hepatocytes. We find that GCs limit the expression of Von Hippel Lindau protein (pVHL), a negative regulator of HIF, and that treatment with the c-src inhibitor PP2 rescued this effect, suggesting a role for GCs in promoting c-src-mediated proteosomal degradation of pVHL. Our data support a model for GCs to stabilize HIF through activation of c-src and subsequent destabilization of pVHL.

PELP1: Structure, biological function and clinical significance

Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein that functions as a coregulator of several transcription factors and nuclear receptors. Notably, the PELP1 protein has a histone-binding domain, recognizes histone modifications and interacts with several chromatin-modifying complexes. PELP1 serves as a substrate of multitude of kinases, and phosphorylation regulates its functions in various complexes. Further, PELP1 plays essential roles in several pathways including hormonal signaling, cell cycle progression, ribosomal biogenesis, and the DNA damage response. PELP1 expression is upregulated in several cancers, its deregulation contributes to therapy resistance, and it is a prognostic biomarker for breast cancer survival. Recent evidence suggests that PELP1 represents a novel therapeutic target for many hormonal cancers. In this review, we summarized the emerging biological properties and functions of PELP1.

Breast Tumor Kinase (Brk/PTK6) Is Induced by HIF, Glucocorticoid Receptor, and PELP1-Mediated Stress Signaling in Triple-Negative Breast Cancer

Cancer cells use stress response pathways to sustain their pathogenic behavior. In breast cancer, stress response-associated phenotypes are mediated by the breast tumor kinase, Brk (PTK6), via the hypoxia-inducible factors HIF-1α and HIF-2α. Given that glucocorticoid receptor (GR) is highly expressed in triple-negative breast cancer (TNBC), we investigated cross-talk between stress hormone-driven GR signaling and HIF-regulated physiologic stress. Primary TNBC tumor explants or cell lines treated with the GR ligand dexamethasone exhibited robust induction of Brk mRNA and protein that was HIF1/2-dependent. HIF and GR coassembled on the BRK promoter in response to either hypoxia or dexamethasone, indicating that Brk is a direct GR/HIF target. Notably, HIF-2α, not HIF-1α, expression was induced by GR signaling, and the important steroid receptor coactivator PELP1 was also found to be induced in a HIF-dependent manner. Mechanistic investigations showed how PELP1 interacted with GR to activate Brk expression and demonstrated that physiologic cell stress, including hypoxia, promoted phosphorylation of GR serine 134, initiating a feed-forward signaling loop that contributed significantly to Brk upregulation. Collectively, our findings linked cellular stress (HIF) and stress hormone (cortisol) signaling in TNBC, identifying the phospho-GR/HIF/PELP1 complex as a potential therapeutic target to limit Brk-driven progression and metastasis in TNBC patients.

The social network of PELP1 and its implications in breast and prostate cancers

Proline, glutamic acid- and leucine-rich protein 1 (PELP1) is a multi-domain scaffold protein that serves as a platform for various protein-protein interactions between steroid receptors (SRs) and signaling factors and cell cycle, transcriptional, cytoskeletal, and epigenetic remodelers. PELP1 is known to be a coregulator of transcription and participates in the nuclear and extranuclear functions of SRs, ribosome biogenesis, and cell cycle progression. The expression and localization of PELP1 are dysregulated in hormonal cancers including breast and prostate cancers. This review focuses on the interactive functions and therapeutic and prognostic significance of PELP1 in breast and prostate cancers.

PELP1 suppression inhibits colorectal cancer through c-Src downregulation

Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1), a coregulator of estrogen receptors alpha and beta, is a potential protooncogene implicated in several human cancers, including sexual hormone-responsive or sexual hormone-nonresponsive cancers. However, the functions of PELP1 in colorectal cancer remain unclear. In this study, western blot and bioinformatics revealed that PELP1 expression was higher in several colorectal cancer cell lines than in immortalized normal colorectal epithelium. PELP1 silencing by short hairpin RNA promoted the senescence and inhibited the proliferation, colony formation, migration, invasion, and xenograft tumor formation of the CRC cell line HT-29. Moreover, PELP1 silencing was accompanied by c-Src downregulation. c-Src upregulation partly alleviated the damage in HT-29 malignant behavior induced by PELP1 RNA interference. In conclusion, PELP1 exhibits an oncogenic function in colorectal cancer through c-Src upregulation.

The histone variant MacroH2A1 regulates target gene expression in part by recruiting the transcriptional coregulator PELP1

MacroH2A1 is a histone variant harboring an ∼25-kDa carboxyl-terminal macrodomain. Due to its enrichment on the inactive X chromosome, macroH2A1 was thought to play a role in transcriptional repression. However, recent studies have shown that macroH2A1 occupies autosomal chromatin and regulates genes in a context-specific manner. The macrodomain may play a role in the modulation of gene expression outcomes via physical interactions with effector proteins, which may depend on the ability of the macrodomain to bind NAD(+) metabolite ligands. Here, we identify proline, glutamic acid, and leucine-rich protein 1 (PELP1), a chromatin-associated factor and transcriptional coregulator, as a ligand-independent macrodomain-interacting factor. We used chromatin immunoprecipitation coupled with tiling microarrays (ChIP-chip) to determine the genomic localization of PELP1 in MCF-7 human breast cancer cells. We find that PELP1 genomic localization is highly correlated with that of macroH2A1. Additionally, PELP1 positively correlates with heterochromatic chromatin marks and negatively correlates with active transcription marks, much like macroH2A1. MacroH2A1 specifically recruits PELP1 to the promoters of macroH2A1 target genes, but macroH2A1 occupancy occurs independent of PELP1. This recruitment allows macroH2A1 and PELP1 to cooperatively regulate gene expression outcomes.

PELP1: a review of PELP1 interactions, signaling, and biology

Proline, glutamic acid, and leucine rich protein 1 (PELP1) is a large multi-domain protein that has been shown to modulate an increasing number of pathways and biological processes. The first reports describing the cloning and characterization of PELP1 showed that it was an estrogen receptor coactivator. PELP1 has now been shown to be a coregulator for a growing number of transcription factors. Furthermore, recent reports have shown that PELP1 is a member of chromatin remodeling complexes. In addition to PELP1 nuclear functions, it has been shown to have cytoplasmic signaling functions as well. In the cytoplasm PELP1 acts as a scaffold molecule and mediates rapid signaling from growth factor and hormone receptors. PELP1 signaling ultimately plays a role in cancer biology by increasing proliferation and metastasis, among other cellular processes. Here we will review (1) the cloning and characterization of PELP1 expression, (2) interacting proteins, (3) PELP1 signaling, and (4) PELP1-mediated biology.

LAS1L interacts with the mammalian Rix1 complex to regulate ribosome biogenesis

The coordination of RNA polymerase I transcription with pre-rRNA processing, preribosomal particle assembly, and nuclear export is a finely tuned process requiring the concerted actions of a number of accessory factors. However, the exact functions of some of these proteins and how they assemble in subcomplexes remain poorly defined. LAS1L was first described as a nucleolar protein required for maturation of the 60S preribosomal subunit. In this paper, we demonstrate that LAS1L interacts with PELP1, TEX10, and WDR18, the mammalian homologues of the budding yeast Rix1 complex, along with NOL9 and SENP3, to form a novel nucleolar complex that cofractionates with the 60S preribosomal subunit. Depletion of LAS1L-associated proteins results in a p53-dependent G1 arrest and leads to defects in processing of the pre-rRNA internal transcribed spacer 2 region. We further show that the nucleolar localization of this complex requires active RNA polymerase I transcription and the small ubiquitin-like modifier-specific protease SENP3. Taken together, our data identify a novel mammalian complex required for 60S ribosomal subunit synthesis, providing further insight into the intricate, yet poorly described, process of ribosome biogenesis in higher eukaryotes.

Loss of glucocorticoid receptor expression by DNA methylation prevents glucocorticoid induced apoptosis in human small cell lung cancer cells

Human small cell lung cancer (SCLC) is highly aggressive, and quickly develops resistance to therapy. SCLC cells are typically insensitive to glucocorticoids due to impaired glucocorticoid receptor (GR) expression. This is important as we have previously shown that expression of a GR transgene induces cell death in-vitro, and inhibits tumor growth in-vivo. However, the underlying mechanism for loss of GR expression is unknown. The SCLC cell line, DMS79, has low GR expression, compared to non-SCLC cell lines and normal bronchial epithelial cells. Retroviral GR expression in DMS79 cells caused activation of the apoptotic pathway as evidenced by marked induction of caspase-3 activity. Methylation analysis of the GR promoter revealed some methylation in the 1D, and 1E promoters of the GR gene, however the ubiquitous constitutively active 1C promoter was heavily methylated. In the 1C promoter there was a highly significant increase in DNA methylation in a panel of 14 human SCLC cell lines compared to a mixed panel of GR expressing, and non-expressing cell lines, and to peripheral blood mononuclear cells. Furthermore, within the panel of SCLC cell lines there was a significant negative correlation seen between methylation of the 1C promoter, and GR protein expression. Reversal of GR gene methylation with DNA methyltransferase inhibition caused increased GR mRNA and protein expression in SCLC but not non-SCLC cells. This resulted in increased Gc sensitivity, decreased Bcl-2 expression and increased caspase-3 activity in SCLC cells. These data suggest that DNA methylation decreases GR gene expression in human SCLC cells, in a similar manner to that for conventional tumor suppressor genes.

Cell cycle phase regulates glucocorticoid receptor function

The glucocorticoid receptor (GR) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. In contrast to many other nuclear receptors, GR is thought to be exclusively cytoplasmic in quiescent cells, and only translocate to the nucleus on ligand binding. We now demonstrate significant nuclear GR in the absence of ligand, which requires nuclear localisation signal 1 (NLS1). Live cell imaging reveals dramatic GR import into the nucleus through interphase and rapid exclusion of the GR from the nucleus at the onset of mitosis, which persists into early G(1). This suggests that the heterogeneity in GR distribution is reflective of cell cycle phase. The impact of cell cycle-driven GR trafficking on a panel of glucocorticoid actions was profiled. In G2/M-enriched cells there was marked prolongation of glucocorticoid-induced ERK activation. This was accompanied by DNA template-specific, ligand-independent GR transactivation. Using chimeric and domain-deleted receptors we demonstrate that this transactivation effect is mediated by the AF1 transactivation domain. AF-1 harbours multiple phosphorylation sites, which are consensus sequences for kinases including CDKs, whose activity changes during the cell cycle. In G2/M there was clear ligand independent induction of GR phosphorylation on residues 203 and 211, both of which are phosphorylated after ligand activation. Ligand-independent transactivation required induction of phospho-S211GR but not S203GR, thereby directly linking cell cycle driven GR modification with altered GR function. Cell cycle phase therefore regulates GR localisation and post-translational modification which selectively impacts GR activity. This suggests that cell cycle phase is an important determinant in the cellular response to Gc, and that mitotic index contributes to tissue Gc sensitivity.

Familial glucocorticoid resistance caused by a novel frameshift glucocorticoid receptor mutation

CONTEXT

Familial glucocorticoid resistance is a rare condition with a typical presentation of women with hirsutism and hypertension, with or without hypokalemia.

OBJECTIVE

The aim was to determine the cause of apparent glucocorticoid resistance in a young woman.

PATIENTS AND METHODS

We studied a family with a novel glucocorticoid receptor (GR) mutation and a surprisingly mild phenotype. Their discovery resulted from serendipitous measurement of serum cortisol with little biochemical or clinical evidence for either hyperandrogenism or mineralocorticoid excess.

RESULTS

The causative mutation was identified as a frameshift mutation in exon 6. Transformed peripheral blood lymphocytes were generated to analyze GR expression in vitro. Carriers of the mutation had less full-length GR, but the predicted mutant GR protein was not detected. However, this does not exclude expression in vivo, and so the mutant GR (Δ612GR) was expressed in vitro. Simple reporter gene assays suggested that Δ612GR has dominant negative activity. Δ612GR was not subject to ligand-dependent Ser211 phosphorylation or to ligand-dependent degradation. A fluorophore-tagged construct showed that Δ612GR did not translocate to the nucleus in response to ligand and retarded translocation of the wild-type GR. These data suggest that Δ612GR is not capable of binding ligand and exerts dominant negative activity through heterodimerization with wild-type GR.

CONCLUSION

Therefore, we describe a novel, naturally occurring GR mutation that results in familial glucocorticoid resistance. The mutant GR protein, if expressed in vivo, is predicted to exert dominant negative activity by impairing wild-type GR nuclear translocation.

Role of glucocorticoids and the glucocorticoid receptor in metabolism: insights from genetic manipulations

Since the discovery of the beneficial effects of adrenocortical extracts for treating adrenal insufficiency more than 80 years ago, glucocorticoids and their cognate, intracellular receptor, the glucocorticoid receptor have been characterized as critical checkpoints in the delicate hormonal control of energy homeostasis in mammals. Whereas physiological levels of glucocorticoids are required for proper metabolic control, aberrant glucocorticoid action has been linked to a variety of pandemic metabolic diseases, such as type II diabetes and obesity. Based on its importance for human health, studies of the molecular mechanisms of within the glucocorticoid signaling axis have become a major focus in biomedical research. In particular, the understanding of tissue-specific functions of the glucocorticoid receptor pathway has been proven to be of substantial value for the development of novel therapies in the treatment of chronic metabolic disorders. Therefore, this review focuses on the consequences of endogenous and experimental modulation of glucocorticoid receptor expression for metabolic homeostasis and dysregulation, particularly emphasizing tissue-specific contributions of the glucocorticoid pathway to the control of energy metabolism.

PELP1: A novel therapeutic target for hormonal cancers

Recent studies implicate that the estrogen receptor (ER) coregulator proline-, glutamic acid-, and leucine-rich protein (PELP) 1 as playing critical roles in ER-genomic, ER-nongenomic, and ER-signaling cross talk with growth factor signaling pathways. PELP1 expression is deregulated in hormonal cancers and recent studies further elucidated the molecular mechanisms by which PELP1 regulates hormone therapy response. Although PELP1 is important for normal functions of the ER, the possibility to target ER-PELP1 axis appears to be an effective strategy for preventing hormonal carcinogenesis and therapy resistance. Thus, PELP1 may be useful as prognostic marker for hormonal cancers and PELP1 signaling may be useful to generate targeted therapeutics to overcome hormonal therapy resistance.