Cytoplasmic Localization of Proline, Glutamic Acid, Leucine-rich Protein 1 (PELP1) Induces Breast Epithelial Cell Migration through Up-regulation of Inhibitor of κB Kinase ϵ and Inflammatory Cross-talk with Macrophages

PELP1 inhibition by SMIP34 reduces endometrial cancer progression via attenuation of ribosomal biogenesis

Endometrial carcinoma (ECa) is the fourth most common cancer among women. The oncogene PELP1 is frequently overexpressed in a variety of cancers, including ECa. We recently generated SMIP34, a small-molecule inhibitor of PELP1 that suppresses PELP1 oncogenic signaling. In this study, we assessed the effectiveness of SMIP34 in treating ECa. Treatment of established and primary patient-derived ECa cells with SMIP34 resulted in a significant reduction of cell viability, colony formation ability, and induction of apoptosis. RNA-seq analyses showed that SMIP34-regulated genes were negatively correlated with ribosome biogenesis and eukaryotic translation pathways. Mechanistic studies showed that the Rix complex, which is essential for ribosomal biogenesis, is disrupted upon SMIP34 binding to PELP1. Biochemical assays confirmed that SMIP34 reduced ribosomal biogenesis and new protein synthesis. Further, SMIP34 enhanced the efficacy of mTOR inhibitors in reducing viability of ECa cells. SMIP34 is also effective in reducing cell viability in ECa organoids in vitro and explants ex vivo. Importantly, SMIP34 treatment resulted in a significant reduction of the growth of ECa xenografts. Collectively, these findings underscore the potential of SMIP34 in treating ECa.

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.

Inflammation-induced PELP1 expression promotes tumorigenesis by activating GM-CSF paracrine secretion in the tumor microenvironment

The inflammatory tumor microenvironment has been implicated as a major player fueling tumor progression and an enabling characteristic of cancer, proline, glutamic acid, and leucine-rich protein 1 (PELP1) is a novel nuclear receptor coregulator that signals across diverse signaling networks, and its expression is altered in several cancers. However, investigations to find the role of PELP1 in inflammation-driven oncogenesis are limited. Molecular studies here, utilizing macrophage cell lines and animal models upon stimulation with lipopolysaccharide (LPS) or necrotic cells, showed that PELP1 is an inflammation-inducible gene. Studies on the PELP1 promoter and its mutant identified potential binding of c-Rel, an NF-κB transcription factor subunit, to PELP1 promoter upon LPS stimulation in macrophages. Recruitment of c-Rel onto the PELP1 promoter was validated by chromatin immunoprecipitation, further confirming LPS mediated PELP1 expression through c-Rel-specific transcriptional regulation. Macrophages that overexpress PELP1 induces granulocyte-macrophage colony-stimulating factor secretion, which mediates cancer progression in a paracrine manner. Results from preclinical studies with normal-inflammatory-tumor progression models demonstrated a progressive increase in the PELP1 expression, supporting this link between inflammation and cancer. In addition, animal studies demonstrated the connection of PELP1 in inflammation-directed cancer progression. Taken together, our findings provide the first report on c-Rel-specific transcriptional regulation of PELP1 in inflammation and possible granulocyte-macrophage colony-stimulating factor-mediated transformation potential of activated macrophages on epithelial cells in the inflammatory tumor microenvironment, reiterating the link between PELP1 and inflammation-induced oncogenesis. Understanding the regulatory mechanisms of PELP1 may help in designing better therapeutics to cure various inflammation-associated malignancies.

Cromolyn platform suppresses fibrosis and inflammation, promotes microglial phagocytosis and neurite outgrowth

Neurodegenerative diseases are characterized by chronic neuroinflammation and may perpetuate ongoing fibrotic reactions within the central nervous system. Unfortunately, there is no therapeutic available that treats neurodegenerative inflammation and its sequelae. Here we utilize cromolyn, a mast cell inhibitor with anti-inflammatory capabilities, and its fluorinated analogue F-cromolyn to study fibrosis-related protein regulation and secretion downstream of neuroinflammation and their ability to promote microglial phagocytosis and neurite outgrowth. In this report, RNA-seq analysis shows that administration of the pro-inflammatory cytokine TNF-α to HMC3 human microglia results in a robust upregulation of fibrosis-associated genes. Subsequent treatment with cromolyn and F-cromolyn resulted in reduced secretion of collagen XVIII, fibronectin, and tenascin-c. Additionally, we show that cromolyn and F-cromolyn reduce pro-inflammatory proteins PLP1, PELP1, HSP90, IL-2, GRO-α, Eotaxin, and VEGF-Α, while promoting secretion of anti-inflammatory IL-4 in HMC3 microglia. Furthermore, cromolyn and F-cromolyn augment neurite outgrowth in PC12 neuronal cells in concert with nerve growth factor. Treatment also differentially altered secretion of neurogenesis-related proteins TTL, PROX1, Rab35, and CSDE1 in HMC3 microglia. Finally, iPSC-derived human microglia more readily phagocytose Aβ42 with cromolyn and F-cromolyn relative to controls. We propose the cromolyn platform targets multiple proteins upstream of PI3K/Akt/mTOR, NF-κB, and GSK-3β signaling pathways to affect cytokine, chemokine, and fibrosis-related protein expression.

Role of estrogen receptor coregulators in endocrine resistant breast cancer

Breast cancer (BC) is the most ubiquitous cancer in women. Approximately 70–80% of BC diagnoses are positive for estrogen receptor (ER) alpha (ERα). The steroid hormone estrogen [17β-estradiol (E2)] plays a vital role both in the initiation and progression of BC. The E2-ERα mediated actions involve genomic signaling and non-genomic signaling. The specificity and magnitude of ERα signaling are mediated by interactions between ERα and several coregulator proteins called coactivators or corepressors. Alterations in the levels of coregulators are common during BC progression and they enhance ligand-dependent and ligand-independent ERα signaling which drives BC growth, progression, and endocrine therapy resistance. Many ERα coregulator proteins function as scaffolding proteins and some have intrinsic or associated enzymatic activities, thus the targeting of coregulators for blocking BC progression is a challenging task. Emerging data from in vitro and in vivo studies suggest that targeting coregulators to inhibit BC progression to therapy resistance is feasible. This review explores the current state of ERα coregulator signaling and the utility of targeting the ERα coregulator axis in treating advanced BC.

PELP1/SRC-3-dependent regulation of metabolic PFKFB kinases drives therapy resistant ER+ breast cancer

Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. Disseminated ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the maintenance and expansion of breast cancer stem cells (CSCs). Breast CSCs frequently exist as a minority population in therapy resistant tumors. In this study, we show that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4. Seahorse metabolic assays demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. PELP1 interacts with PFKFB3 and PFKFB4 proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB4 knockdown inhibited in vivo emergence of circulating tumor cell (CTC) populations in mammary intraductal (MIND) models. Application of PFKFB inhibitors in combination with ER targeted therapies blocked tumorsphere formation in multiple models of advanced breast cancer including tamoxifen (TamR) and paclitaxel (TaxR) resistant models, murine tumor cells, and ER+ patient-derived organoids (PDxO). Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cell populations that include CSCs and CTCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance.

PELP1 signaling contributes to medulloblastoma progression by regulating the NF-κB pathway

Medulloblastoma (MB) is the most common and deadliest brain tumor in children. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein and its oncogenic signaling is implicated in the progression of several cancers. However, the role of PELP1 in the progression of MB remains unknown. The objective of this study is to examine the role of PELP1 in the progression of MB. Immunohistochemical analysis of MB tissue microarrays revealed that PELP1 is overexpressed in the MB specimens compared to normal brain. Knockdown of PELP1 reduced cell proliferation, cell survival, and cell invasion of MB cell lines. The RNA-sequencing analysis revealed that PELP1 knockdown significantly downregulated the pathways related to inflammation and extracellular matrix. Gene set enrichment analysis confirmed that the PELP1-regulated genes were negatively correlated with nuclear factor-κB (NF-κB), extracellular matrix, and angiogenesis gene sets. Interestingly, PELP1 knockdown reduced the expression of NF-κB target genes, NF-κB reporter activity, and inhibited the nuclear translocation of p65. Importantly, the knockdown of PELP1 significantly reduced in vivo MB progression in orthotopic models and improved the overall mice survival. Collectively, these results suggest that PELP1 could be a novel target for therapeutic intervention in MB.

Cancer Stem Cell Phenotypes in ER+ Breast Cancer Models Are Promoted by PELP1/AIB1 Complexes

Proline, glutamic acid, leucine-rich protein 1 (PELP1) is overexpressed in approximately 80% of invasive breast tumors. PELP1 dynamically shuttles between the nucleus and cytoplasm, but is primarily nuclear in normal breast tissue. However, altered localization of PELP1 to the cytoplasm is an oncogenic event that promotes breast cancer initiation and progression. Herein, interacting partners unique to cytoplasmic PELP1 and the mechanisms by which these interactions promote oncogenic PELP1 signaling were sought. AIB1 (amplified in breast cancer 1; also known as SRC-3 or NCOA3) was identified as a novel binding partner of cytoplasmic PELP1 in both estrogen receptor-positive (ER+) and ER-negative cell lines. Cytoplasmic PELP1 expression elevated basal phosphorylation levels (i.e., activation) of AIB1 at Thr24, enhanced ALDH+ tumorsphere formation, and upregulated specific target genes independently of hormone stimulation. Direct manipulation of AIB1 levels using shRNA abrogated cytoplasmic PELP1-induced tumorsphere formation and downregulated cytoplasmic PELP1-specific target genes. SI-2, an AIB1 inhibitor, limited the PELP1/AIB1 interaction and decreased cytoplasmic PELP1-induced tumorsphere formation. Similar results were observed in a murine-derived MMTV-AIB1 tumor cell line. Furthermore, in vivo syngeneic tumor studies revealed that PELP1 knockdown resulted in increased survival of tumor-bearing mice as compared with mice injected with control cells.Implications: These data demonstrate that cytoplasmic PELP1/AIB1-containing complexes function to promote advanced cancer phenotypes, including outgrowth of stem-like cells, associated with estrogen-independent breast cancer progression. Mol Cancer Res; 16(4); 707-19. ©2018 AACR.