Translational regulation of inhibin βA by TGFβ via the RNA-binding protein hnRNP E1 enhances the invasiveness of epithelial-to-mesenchymal transitioned cells

New therapeutic approaches for fibrosis: harnessing translational regulation

Idiopathic pulmonary fibrosis (IPF) is a progressive and debilitating lung disease characterized by excessive extracellular matrix deposition and tissue scarring. The median survival of patients with IPF is only 4.5 years following diagnosis, and effective treatment options are scarce. Recent studies found aberrant translation of specific mRNAs in various fibrosing diseases, highlighting the role of key translational regulators, including RNA binding proteins (RBPs), microRNAs, long noncoding RNAs, and transcript modifications. Notably, when inhibited, 10 profibrotic RBPs cause a significant attenuation of fibrosis, illuminating potential therapeutic targets. In this review, we describe translational regulation in fibrosis and highlight a model where a conserved evolutionary mechanism may explain this regulation.

Elevated INHBA Promotes Tumor Progression of Cervical Cancer

Objectives: This study aimed to explore the role of inhibin subunit beta A (INHBA) in the progression of cervical cancer (CCa) and investigate its potential as a therapeutic target. Specifically, the objectives were to assess the expression levels of INHBA in CCa, examine its correlation with patient survival, and elucidate its impact on CCa cell proliferation, cell cycle regulation, migration, invasion, and in vivo tumor growth and metastasis. Methods: To achieve the objectives, we conducted a comprehensive set of experimental methods. INHBA expression in CCa was analyzed, and its association with patient survival was assessed using clinical data. In vitro experiments involved the investigation of INHBA's effects on CCa cell proliferation, cell cycle dynamics, migration, and invasion through the epithelial-mesenchymal transition (EMT) process. Additionally, in vivo experiments were performed to evaluate the influence of INHBA on CCa growth and lung metastasis. Results: The results of this study revealed upregulated expression of INHBA in CCa, with a significant association between high INHBA expression and poor patient survival. Functionally, INHBA was found to promote the proliferation of CCa cells, regulate the cell cycle, and enhance migration and invasion through the EMT process in vitro. Moreover, in vivo experiments demonstrated that INHBA facilitated the growth and lung metastasis of CCa. Conclusion: In conclusion, our findings suggest that INHBA plays a crucial role in the progression of cervical cancer. The upregulation of INHBA is associated with poor patient survival, and its involvement in promoting key aspects of cancer progression makes it a potential therapeutic target for CCa treatment. These results provide valuable insights into the molecular mechanisms underlying CCa and offer a foundation for further exploration of targeted therapeutic interventions.

PCBP1 regulates LIFR through FAM3C to maintain breast cancer stem cell self-renewal and invasiveness

The poly(rC) binding protein 1 gene (PCBP1) encodes the heterogeneous nuclear ribonucleoprotein E1 (hnRNPE1), a nucleic acid-binding protein that plays a tumor-suppressive role in the mammary epithelium by regulating phenotypic plasticity and cell fate. Following the loss of PCBP1 function, the FAM3C gene (encoding the Interleukin-like EMT inducer, or "ILEI" protein) and the leukemia inhibitory factor receptor (LIFR) gene are upregulated. Interaction between FAM3C and LIFR in the extracellular space induces phosphorylation of signal transducer and activator of transcription 3 (pSTAT3). Overexpression and/or hyperactivity of STAT3 has been detected in 40% of breast cancer cases and is associated with a poor prognosis. Herein, we characterize feed-forward regulation of LIFR expression in response to FAM3C/LIFR/STAT3 signaling in mammary epithelial cells. We show that PCBP1 upregulates LIFR transcription through activity at the LIFR promoter, and that FAM3C participates in transcriptional regulation of LIFR. Additionally, our bioinformatic analysis reveals a signature of transcriptional regulation associated with FAM3C/LIFR interaction and identifies the TWIST1 transcription factor as a downstream effector that participates in the maintenance of LIFR expression. Finally, we characterize the effect of LIFR expression in cell-based experiments that demonstrate the promotion of invasion, migration, and self-renewal of breast cancer stem cells (BCSCs), consistent with previous studies linking LIFR expression to tumor initiation and metastasis in mammary epithelial cells.

RNA binding proteins (RBPs) and their role in DNA damage and radiation response in cancer

Traditionally majority of eukaryotic gene expression is influenced by transcriptional and post-transcriptional events. Alterations in the expression of proteins that act post-transcriptionally can affect cellular signaling and homeostasis. RNA binding proteins (RBPs) are a family of proteins that specifically bind to RNAs and are involved in post-transcriptional regulation of gene expression and important cellular processes such as cell differentiation and metabolism. Deregulation of RNA-RBP interactions and any changes in RBP expression or function can lead to various diseases including cancer. In cancer cells, RBPs play an important role in regulating the expression of tumor suppressors and oncoproteins involved in various cell-signaling pathways. Several RBPs such as HuR, AUF1, RBM38, LIN28, RBM24, tristetrapolin family and Musashi play critical roles in various types of cancers and their aberrant expression in cancer cells makes them an attractive therapeutic target for cancer treatment. In this review we provide an overview of i). RBPs involved in cancer progression and their mechanism of action ii). the role of RBPs, including HuR, in breast cancer progression and DNA damage response and iii). explore RBPs with emphasis on HuR as therapeutic target for breast cancer therapy.

RNA-binding proteins and cancer metastasis

RNA-binding proteins (RBPs) can regulate gene expression through post-transcriptionally influencing all manner of RNA biology, including alternative splicing (AS), polyadenylation, stability, and translation of mRNAs, as well as microRNAs (miRNAs) and circular RNAs (circRNAs) processing. There is accumulating evidence reinforcing the perception that dysregulation or dysfunction of RBPs can lead to various human diseases, including cancers. RBPs influence diverse cancer-associated cellular phenotypes, such as proliferation, apoptosis, senescence, migration, invasion, and angiogenesis, contributing to the initiation and development of tumors, as well as clinical prognosis. Metastasis is the leading cause of cancer-related recurrence and death. Therefore, it is necessary to elucidate the molecular mechanisms behind tumor metastasis. In fact, a growing body of published research has proved that RBPs play pivotal roles in cancer metastasis. In this review, we will summarize the recent advances for helping us understand the role of RBPs in tumor metastasis, and discuss dysfunctions and dysregulations of RBPs affecting metastasis-associated processes including epithelial-mesenchymal transition (EMT), migration, and invasion of cancer cells. Furthermore, we will discuss emerging RBP-based strategy for the treatment of cancer metastasis.

Heterogeneity and dynamic of EMT through the plasticity of ribosome and mRNA translation

Growing evidence exposes translation and its translational machinery as key players in establishing and maintaining physiological and pathological biological processes. Examining translation may not only provide new biological insight but also identify novel innovative therapeutic targets in several fields of biology, including that of epithelial-to-mesenchymal transition (EMT). EMT is currently considered as a dynamic and reversible transdifferentiation process sustaining the transition from an epithelial to mesenchymal phenotype, known to be mainly driven by transcriptional reprogramming. However, it seems that the characterization of EMT plasticity is challenging, relying exclusively on transcriptomic and epigenetic approaches. Indeed, heterogeneity in EMT programs was reported to depend on the biological context. Here, by reviewing the involvement of translational control, translational machinery and ribosome biogenesis characterizing the different types of EMT, from embryonic and adult physiological to pathological contexts, we discuss the added value of integrating translational control and its machinery to depict the heterogeneity and dynamics of EMT programs.

Drug delivery approaches for HuR-targeted therapy for lung cancer

Lung cancer (LC) is often diagnosed at an advanced stage and conventional treatments for disease management have limitations associated with them. Novel therapeutic targets are thus avidly sought for the effective management of LC. RNA binding proteins (RBPs) have been convincingly established as key players in tumorigenesis, and their dysregulation is linked to multiple cancers, including LC. In this context, we review the role of Human antigen R (HuR), an RBP that is overexpressed in LC, and further associated with various aspects of LC tumor growth and response to therapy. Herein, we describe the role of HuR in LC progression and outline the evidences supporting various pharmacologic and biologic approaches for inhibiting HuR expression and function. These approaches, including use of small molecule inhibitors, siRNAs and shRNAs, have demonstrated favorable results in reducing tumor cell growth, invasion and migration, angiogenesis and metastasis. Hence, HuR has significant potential as a key therapeutic target in LC. Use of siRNA-based approaches, however, have certain limitations that prevent their maximal exploitation as cancer therapies. To address this, in the conclusion of this review, we provide a list of nanomedicine-based HuR targeting approaches currently being employed for siRNA and shRNA delivery, and provide a rationale for the immense potential therapeutic benefits offered by nanocarrier-based HuR targeting and its promise for treating patients with LC.

The ubiquitin E3 ligase ARIH1 regulates hnRNP E1 protein stability, EMT and breast cancer progression

The epithelial to mesenchymal transition (EMT), a process that is aberrantly activated in cancer and facilitates metastasis to distant organs, requires coordinated transcriptional and post-transcriptional control of gene expression. The tumor-suppressive RNA binding protein, hnRNP-E1, regulates splicing and translation of EMT-associated transcripts and it is thought that it plays a major role in the control of epithelial cell plasticity during cancer progression. We have utilized yeast 2 hybrid screening to identify novel hnRNP-E1 interactors that play a role in regulating hnRNP-E1; this approach led to the identification of the E3 ubiquitin ligase ARIH1. Here, we demonstrate that hnRNP-E1 protein stability is increased upon ARIH1 silencing, whereas, overexpression of ARIH1 leads to a reduction in hnRNP-E1. Reduced ubiquitination of hnRNP-E1 detected in ARIH1 knockdown (KD) cells compared to control suggests a role for ARIH1 in hnRNP-E1 degradation. The identification of hnRNP-E1 as a candidate substrate of ARIH1 led to the characterization of a novel function for this ubiquitin ligase in EMT induction and cancer progression. We demonstrate a delayed induction of EMT and reduced invasion in mammary epithelial cells silenced for ARIH1. Conversely, ARIH1 overexpression promoted EMT induction and invasion. ARIH1 silencing in breast cancer cells significantly attenuated cancer cell stemness in vitro and tumor formation in vivo. Finally, we utilized miniTurboID proximity labeling to identify novel ARIH1 interactors that may contribute to ARIH1's function in EMT induction and cancer progression.

GARP: A Key Target to Evaluate Tumor Immunosuppressive Microenvironment

Simple Summary

Tumors are not only composed of cancer cells but also of various infiltrating cells constituting the tumor microenvironment (TME); all these cells produce growth factors which contribute to tumor progression and invasiveness. Among them, transforming growth factor-β1 (TGF-β1) has been shown to be a potent immunosuppressive cytokine favoring cell proliferation and invasion and to be associated with resistance to anticancer treatments. Glycoprotein-A repetition predominant (GARP) plays a critical role in the activation of TGF-β1 and has been shown to be expressed at the membrane of cancer cells and also of regulatory T cells and platelets in the TME. An increased GARP expression has been shown in a variety of cancers. The objective of this review is to highlight GARP’s expression and function in cancer and to evaluate its potential as a predictive and therapeutic follow-up biomarker that could be assessed, in real time, by molecular imaging.

Abstract

Glycoprotein-A repetitions predominant (GARP) is the docking receptor for latent transforming growth factor (LTGF-β) and promotes its activation. In cancer, increased GARP expression has been found in many types of cancer. GARP is expressed by regulatory T cells and platelets in the tumor microenvironment (TME) and can be also expressed by tumor cells themselves. Thus, GARP can be widely present in tumors in which it plays a major role in the production of active TGF-β, contributing to immune evasion and cancer progression via the GARP-TGF-β pathway. The objective of this review is to highlight GARP expression and function in cancer and to evaluate the potential of membrane GARP as a predictive and therapeutic follow-up biomarker that could be assessed, in real time, by molecular imaging. Moreover, as GARP can be secreted, a focus will also be made on soluble GARP as a circulating biomarker.

Multilevel regulation and molecular mechanism of poly (rC)-binding protein 1 in cancer

Poly (rC)-binding protein 1 (PCBP1), an RNA- or DNA-binding protein with a relative molecular weight of 38 kDa, which is characterized by downregulation in many cancer types. Numerous cases have indicated that PCBP1 could be considered as a tumor suppressor to inhibit tumorigenesis, development, and metastasis. In the current review, we described the multilevel regulatory roles of PCBP1, including gene transcription, alternative splicing, and translation of many cancer-related genes. Additionally, we also provided a brief overview about the inhibitory effect of PCBP1 on most common tumors. More importantly, we summarized the current research status about PCBP1 in hypoxic microenvironment, autophagy, apoptosis, and chemotherapy of cancer cells, aiming to clarify the molecular mechanisms of PCBP1 in cancer. Taken together, in-depth study of PCBP1 in cancer may provide new ideas for cancer therapy.

RNA-Binding Proteins in Cancer: Functional and Therapeutic Perspectives

Simple Summary

RNA-binding proteins (RBPs) play central roles in regulating posttranscriptional expression of genes. Many of them are known to be deregulated in a wide variety of cancers. Dysregulated RBPs influence the expression levels of target RNAs related to cancer phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and EMT/invasion/metastasis. Thus, understanding the molecular functions of RBPs and their roles in cancer-related phenotypes can lead to improved therapeutic strategies.

Abstract

RNA-binding proteins (RBPs) crucially regulate gene expression through post-transcriptional regulation, such as by modulating microRNA (miRNA) processing and the alternative splicing, alternative polyadenylation, subcellular localization, stability, and translation of RNAs. More than 1500 RBPs have been identified to date, and many of them are known to be deregulated in cancer. Alterations in the expression and localization of RBPs can influence the expression levels of oncogenes, tumor-suppressor genes, and genome stability-related genes. RBP-mediated gene regulation can lead to diverse cancer-related cellular phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and epithelial-mesenchymal transition (EMT)/invasion/metastasis. This regulation can also be associated with cancer prognosis. Thus, RBPs can be potential targets for the development of therapeutics for the cancer treatment. In this review, we describe the molecular functions of RBPs, their roles in cancer-related cellular phenotypes, and various approaches that may be used to target RBPs for cancer treatment.

New markers for regulation of transcription and macromolecule metabolic process in porcine oocytes during in vitro maturation

Oocyte maturation is essential for proper fertilization, embryo implantation and early development. While the physiological conditions of these processes are relatively well-known, its exact molecular mechanisms remain widely undiscovered. Oocyte growth, differentiation and maturation are therefore the subject of scientific debate. Precious literature has indicated that the oocyte itself serves a regulatory role in the mechanisms underlying these processes. Hence, the present study performed expression microarrays to analyze the complete transcriptome of porcine oocytes during their in vitro maturation (IVM). Pig material was used for experimentation, as it possesses similarities to the reproductive processes and general genetic proximities of Sus scrofa to human. Oocytes, isolated from the ovaries of slaughtered animals were assessed via the Brilliant Cresyl Blue test and directed to IVM. A number of oocytes were left to be analyzed as the ‘before IVM’ group. Oocyte mRNA was isolated and used for microarray analysis, which was subsequently validated via RT-qPCR. The current study particularly focused on genes belonging to ‘positive regulation of transcription, DNA-dependent’, ‘positive regulation of gene expression’, ‘positive regulation of macromolecule metabolic process’ and ‘positive regulation of transcription from RNA polymerase II promoter’ ontologies. FOS, VEGFA, ESR1, AR, CCND2, EGR2, ENDRA, GJA1, INHBA, IHH, INSR, APP, WWTR1, SMARCA1, NFAT5, SMAD4, MAP3K1, EGR1, RORA, ECE1, NR5A1, KIT, IKZF2, MEF2C, SH3D19, MITF and PSMB4 were all determined to be significantly altered (fold change, >|2|; P<0.05) among these groups, with their downregulation being observed after IVM. Genes with the most altered expressions were analyzed and considered to be potential markers of maturation associated with transcription regulation and macromolecule metabolism process.

KH-Domain Poly(C)-Binding Proteins as Versatile Regulators of Multiple Biological Processes

Five known members of the family of KH-domain poly(C)-binding proteins (Pcbp1-4, hnRNP-K) have an unusually broad spectrum of cellular functions that include regulation of gene transcription, regulation of pre-mRNA processing, splicing, mRNA stability, translational silencing and enhancement, the control of iron turnover, and many others. Mechanistically, these proteins act via nucleic acid binding and protein-protein interactions. Through performing these multiple tasks, the KH-domain poly(C)-binding family members are involved in a wide variety of biological processes such as embryonic development, cell differentiation, and cancer. Deregulation of KH-domain protein expression is frequently associated with severe developmental defects and neoplasia. This review summarizes progress in studies of the KH-domain proteins made over past two decades. The review also reports our recent finding implying an involvement of the KH-factor Pcbp1 into control of transition from naïve to primed pluripotency cell state.

TGFβ promotes breast cancer stem cell self-renewal through an ILEI/LIFR signaling axis

FAM3C/Interleukin-like EMT Inducer (ILEI) is an oncogenic member of the FAM3 cytokine family and serves essential roles in both epithelial-mesenchymal transition (EMT) and breast cancer metastasis. ILEI expression levels are regulated through a non-canonical TGFβ signaling pathway by 3'-UTR-mediated translational silencing at the mRNA level by hnRNP E1. TGFβ stimulation or silencing of hnRNP E1 increases ILEI translation and induces an EMT program that correlates with enhanced invasion and migration. Recently, EMT has been linked to the formation of breast cancer stem cells (BCSCs) that confer both tumor cell heterogeneity as well as chemoresistant properties. Herein, we demonstrate that hnRNP E1 knockdown significantly shifts normal mammary epithelial cells to mesenchymal BCSCs in vitro and in vivo. We further validate that modulating ILEI protein levels results in the abrogation of these phenotypes, promoting further investigation into the unknown mechanism of ILEI signaling that drives tumor progression. We identify LIFR as the receptor for ILEI, which mediates signaling through STAT3 to drive both EMT and BCSC formation. Reduction of either ILEI or LIFR protein levels results in reduced tumor growth, fewer tumor initiating cells and reduced metastasis within the hnRNP E1 knock-down cell populations in vivo. These results reveal a novel ligand-receptor complex that drives the formation of BCSCs and represents a unique target for the development of metastatic breast cancer therapies.

INHBA gene silencing inhibits gastric cancer cell migration and invasion by impeding activation of the TGF-β signaling pathway

Gastric cancer (GC) is the fourth largest cancer in the world, with a 5-year survival rate of <30%. Thus, this study intends to investigate the effects of inhibin βA (INHBA) gene silencing on the migration and invasion of GC cells via the transforming growth factor-β (TGF-β) signaling pathway. Initially, this study determined the expression of INHBA and the TGF-β signaling pathway-related genes in GC tissues. After that, to assess the effect of INHBA silencing on GC progression, GC cells were transfected with short hairpin RNAs that targeted INHBA in order to detect the expression of INHBA and the TGF-β signaling pathway-related genes, as well as cell migration, invasion, and proliferation abilities. Finally, a tumor xenograft model in nude mice was constructed to verify the effect that the silencing of INHBA had on tumor growth. Highly expressed INHBA and activated TGF-β signaling pathways were observed in GC tissues. In response to shINHBA-1 and shINHBA-2, the TGF-β signaling pathway was inhibited in GC cells, whereas the GC cell migration, invasion, proliferation, and tumor growth were significantly dampened. On the basis of the observations and findings of this study, INHBA gene silencing inhibited the progression of GC by inactivating the TGF-β signaling pathway, which provides a potential target in the treatment of GC.

Epithelial-Mesenchymal Transition and Metastasis under the Control of Transforming Growth Factor β

Metastasis of tumor cells from primary sites of malignancy to neighboring stromal tissue or distant localities entails in several instances, but not in every case, the epithelial-mesenchymal transition (EMT). EMT weakens the strong adhesion forces between differentiated epithelial cells so that carcinoma cells can achieve solitary or collective motility, which makes the EMT an intuitive mechanism for the initiation of tumor metastasis. EMT initiates after primary oncogenic events lead to secondary secretion of cytokines. The interaction between tumor-secreted cytokines and oncogenic stimuli facilitates EMT progression. A classic case of this mechanism is the cooperation between oncogenic Ras and the transforming growth factor β (TGFβ). The power of TGFβ to mediate EMT during metastasis depends on versatile signaling crosstalk and on the regulation of successive waves of expression of many other cytokines and the progressive remodeling of the extracellular matrix that facilitates motility through basement membranes. Since metastasis involves many organs in the body, whereas EMT affects carcinoma cell differentiation locally, it has frequently been debated whether EMT truly contributes to metastasis. Despite controversies, studies of circulating tumor cells, studies of acquired chemoresistance by metastatic cells, and several (but not all) metastatic animal models, support a link between EMT and metastasis, with TGFβ, often being a common denominator in this link. This article aims at discussing mechanistic cases where TGFβ signaling and EMT facilitate tumor cell dissemination.

hnRNPDL extensively regulates transcription and alternative splicing

RNA binding proteins (RBPs) are key players of genome regulation. Here we report the transcriptome study of HnRNP D-Like protein, which belongs to the hnRNP family. We used RNA-seq to analyze the global transcript level and alternative splicing on hnRNPDL shRNA-treated cells and control. Sh-hnRNPDL extensively increased in the expression of genes involved in female pregnancy, cell apoptosis, cell proliferation and cell migration. HnRNPDL regulated alternative splicing of hundreds of genes enriched in transcription regulation and signaling pathways including NOD-like receptor signaling, Notch signaling, and TNF signaling. This study provides the first transcriptome-wide analysis of hnRNPDL regulation of gene expression, which adds to the understanding of critical hnRNPDL functions.

Identification of key pathways and genes in lung carcinogenesis

The present study aimed to identify key pathways and genes in the pathogenesis of lung cancer. The GSE10072 dataset was downloaded from the Gene Expression Omnibus database. Protein-protein interaction data were collected from Human Protein Reference Database, and 201 pathways were downloaded from the Kyoto Encyclopedia of Genes and Genomes database. Signaling network impact analysis was performed to identify enriched pathways, followed by the construction of a pathway-pathway crosstalk network. Benzopyrene was used to treat normal human lung cells at concentrations of 0.01, 0.1, 1 and 10 µM, and cell viability was measured. Furthermore, growth arrest and DNA damage inducible β (GADD45B), p53, cyclin B, Akt and nuclear factor (NF)-κB protein levels were also measured via western blotting. Impact analysis identified 11 enriched lung cancer-associated KEGG pathways, including 'complement and coagulation cascades', 'ECM-receptor interaction', 'P53 signaling pathway', 'cell adhesion molecules' and 'focal adhesion'. In addition, cell cycle, 'drug metabolism-cytochrome P450', 'metabolic pathways', 'pathways in cancer', 'focal adhesion' and 'antigen processing and presentation' were central in the pathway-pathway cross-talk network. Furthermore, the upregulated gene GADD45B was associated with three of the pathways, including an activated pathway ('MAPK signaling pathway') and two repressed pathways ('cell cycle' and 'P53 pathway'). Western blotting demonstrated that the expression of NF-κB, Akt and GADD45B increased over time in lung cells treated with benzopyrene, whereas the expression levels of cyclin B and P53 decreased. In conclusion, GADD45B may contribute to lung carcinogenesis via affecting the MAPK, P53 signaling and cell cycle pathways.

Splicing factor poly(rC)-binding protein 1 is a novel and distinctive tumor suppressor

A lot of evidence has been found on the link between tumorigenesis and the aberrant expression of splicing factors. A number of splicing factors have been reported to be either oncogenic or overexpressed in cancer cells. However, splicing factors can also play negative roles in tumorigenesis. In the current review, we focus on splicing factor poly(rC)-binding protein 1 (PCBP1), a novel tumor suppressor that is characterized by downregulation in many cancer types and shows inhibition of tumor formation and metastasis. Notably, the messenger RNA levels of PCBP1 are not significantly decreased in most cancer types. In fact, PCBP1 protein is often degraded or shows a loss-of-function through phosphorylation in cancer cells. PCBP1 is highly homologous to its family member, PCBP2. Interestingly, PCBP2 appears to be an oncogenic splicing factor. A growing body of evidence has shown that PCBP1 regulates alternative splicing, translation, and RNA stability of many cancer-related genes. Taking together, PCBP1 has distinctive tumor suppressive functions, and increasing PCBP1 expression may represent a new approach for cancer treatment.

Genome-wide strategies identify downstream target genes of chick connective tissue-associated transcription factors

Connective tissues support organs and play crucial roles in development, homeostasis and fibrosis, yet our understanding of their formation is still limited. To gain insight into the molecular mechanisms of connective tissue specification, we selected five zinc-finger transcription factors - OSR1, OSR2, EGR1, KLF2 and KLF4 - based on their expression patterns and/or known involvement in connective tissue subtype differentiation. RNA-seq and ChIP-seq profiling of chick limb micromass cultures revealed a set of common genes regulated by all five transcription factors, which we describe as a connective tissue core expression set. This common core was enriched with genes associated with axon guidance and myofibroblast signature, including fibrosis-related genes. In addition, each transcription factor regulated a specific set of signalling molecules and extracellular matrix components. This suggests a concept whereby local molecular niches can be created by the expression of specific transcription factors impinging on the specification of local microenvironments. The regulatory network established here identifies common and distinct molecular signatures of limb connective tissue subtypes, provides novel insight into the signalling pathways governing connective tissue specification, and serves as a resource for connective tissue development.

A CREB3-regulated ER-Golgi trafficking signature promotes metastatic progression in breast cancer

In order to better understand the process of breast cancer metastasis, we have generated a mammary epithelial progression series of increasingly aggressive cell lines that metastasize to lung. Here we demonstrate that upregulation of an endoplasmic reticulum (ER) to Golgi trafficking gene signature in metastatic cells enhances transport kinetics, which promotes malignant progression. We observe increased ER-Golgi trafficking, an altered secretome and sensitivity to the retrograde transport inhibitor brefeldin A (BFA) in cells that metastasize to lung. CREB3 was identified as a transcriptional regulator of upregulated ER-Golgi trafficking genes ARF4, COPB1, and USO1, and silencing of these genes attenuated the metastatic phenotype in vitro and lung colonization in vivo. Furthermore, high trafficking gene expression significantly correlated with increased risk of distant metastasis and reduced relapse-free and overall survival in breast cancer patients, suggesting that modulation of ER-Golgi trafficking plays an important role in metastatic progression.

TGF-beta signaling in cancer: post-transcriptional regulation of EMT via hnRNP E1

The TGFβ signaling pathway is a critical regulator of cancer progression in part through induction of the epithelial to mesenchymal transition (EMT). This process is aberrantly activated in cancer cells, facilitating invasion of the basement membrane, survival in the circulatory system, and dissemination to distant organs. The mechanisms through which epithelial cells transition to a mesenchymal state involve coordinated transcriptional and post-transcriptional control of gene expression. One such mechanism of control is through the RNA binding protein hnRNP E1, which regulates splicing and translation of a cohort of EMT and stemness-associated transcripts. A growing body of evidence indicates a major role for hnRNP E1 in the control of epithelial cell plasticity, especially in the context of carcinoma progression. Here, we review the multiple mechanisms through which hnRNP E1 functions to control EMT and metastatic progression.

Activin signaling is an essential component of the TGF-β induced pro-metastatic phenotype in colorectal cancer

Advanced colorectal cancer (CRC) remains a critical health care challenge worldwide. Various TGF-β superfamily members are important in colorectal cancer metastasis, but their signaling effects and predictive value have only been assessed in isolation. Here, we examine cross-regulation and combined functions of the two most prominent TGF-β superfamily members activin and TGF-β in advanced colorectal cancer. In two clinical cohorts we observed by immune-based assay that combined serum and tissue activin and TGF-β ligand levels predicts outcome in CRC patients and is superior to single ligand assessment. While TGF-β growth suppression is independent of activin, TGF-β treatment leads to increased activin secretion in colon cancer cells and TGF-β induced cellular migration is dependent on activin, indicating pathway cross-regulation and functional interaction in vitro. mRNA expression of activin and TGF-β pathway members were queried in silico using the TCGA data set. Coordinated ligand and receptor expression is common in solid tumors for activin and TGF-β pathway members. In conclusion, activin and TGF-β are strongly connected signaling pathways that are important in advanced CRC. Assessing activin and TGF-β signaling as a unit yields important insights applicable to future diagnostic and therapeutic interventions.

Interleukin-like EMT inducer regulates partial phenotype switching in MITF-low melanoma cell lines

ILEI (FAM3C) is a secreted factor that contributes to the epithelial-to-mesenchymal transition (EMT), a cell biological process that confers metastatic properties to a tumor cell. Initially, we found that ILEI mRNA is highly expressed in melanoma metastases but not in primary tumors, suggesting that ILEI contributes to the malignant properties of melanoma. While melanoma is not an epithelial cell-derived tumor and does not undergo a traditional EMT, melanoma undergoes a similar process known as phenotype switching in which high (micropthalmia-related transcription factor) MITF expressing (MITF-high) proliferative cells switch to a low expressing (MITF-low) invasive state. We observed that MITF-high proliferative cells express low levels of ILEI (ILEI-low) and MITF-low invasive cells express high levels of ILEI (ILEI-high). We found that inducing phenotype switching towards the MITF-low invasive state increases ILEI mRNA expression, whereas phenotype switching towards the MITF-high proliferative state decreases ILEI mRNA expression. Next, we used in vitro assays to show that knockdown of ILEI attenuates invasive potential but not MITF expression or chemoresistance. Finally, we used gene expression analysis to show that ILEI regulates several genes involved in the MITF-low invasive phenotype including JARID1B, HIF-2α, and BDNF. Gene set enrichment analysis suggested that ILEI-regulated genes are enriched for JUN signaling, a known regulator of the MITF-low invasive phenotype. In conclusion, we demonstrate that phenotype switching regulates ILEI expression, and that ILEI regulates partial phenotype switching in MITF-low melanoma cell lines.

Mutant HSPB1 causes loss of translational repression by binding to PCBP1, an RNA binding protein with a possible role in neurodegenerative disease

The small heat shock protein HSPB1 (Hsp27) is an ubiquitously expressed molecular chaperone able to regulate various cellular functions like actin dynamics, oxidative stress regulation and anti-apoptosis. So far disease causing mutations in HSPB1 have been associated with neurodegenerative diseases such as distal hereditary motor neuropathy, Charcot-Marie-Tooth disease and amyotrophic lateral sclerosis. Most mutations in HSPB1 target its highly conserved α-crystallin domain, while other mutations affect the C- or N-terminal regions or its promotor. Mutations inside the α-crystallin domain have been shown to enhance the chaperone activity of HSPB1 and increase the binding to client proteins. However, the HSPB1-P182L mutation, located outside and downstream of the α-crystallin domain, behaves differently. This specific HSPB1 mutation results in a severe neuropathy phenotype affecting exclusively the motor neurons of the peripheral nervous system. We identified that the HSPB1-P182L mutant protein has a specifically increased interaction with the RNA binding protein poly(C)binding protein 1 (PCBP1) and results in a reduction of its translational repressive activity. RNA immunoprecipitation followed by RNA sequencing on mouse brain lead to the identification of PCBP1 mRNA targets. These targets contain larger 3′- and 5′-UTRs than average and are enriched in an RNA motif consisting of the CTCCTCCTCCTCC consensus sequence. Interestingly, next to the clear presence of neuronal transcripts among the identified PCBP1 targets we identified known genes associated with hereditary peripheral neuropathies and hereditary spastic paraplegias. We therefore conclude that HSPB1 can mediate translational repression through interaction with an RNA binding protein further supporting its role in neurodegenerative disease.

Post-transcriptional regulation of cytokine and growth factor signaling in cancer

Cytokines and growth factors regulate cell proliferation, differentiation, migration and apoptosis, and play important roles in coordinating growth signal responses during development. The expression of cytokine genes and the signals transmitted through cytokine receptors are tightly regulated at several levels, including transcriptional and post-transcriptional levels. A majority of cytokine mRNAs, including growth factor transcripts, contain AU-rich elements (AREs) in their 3' untranslated regions that control gene expression by regulating mRNA degradation and changing translational rates. In addition, numerous proteins involved in transmitting signals downstream of cytokine receptors are regulated at the level of mRNA degradation by GU-rich elements (GREs) found in their 3' untranslated regions. Abnormal stabilization and overexpression of ARE or GRE-containing transcripts had been observed in many malignancies, which is a consequence of the malfunction of RNA-binding proteins. In this review, we briefly summarize the role of AREs and GREs in regulating mRNA turnover to coordinate cytokine and growth factor expression, and we describe how dysregulation of mRNA degradation mechanisms contributes to the development and progression of cancer.

Surface Expression of TGFβ Docking Receptor GARP Promotes Oncogenesis and Immune Tolerance in Breast Cancer

GARP encoded by the Lrrc32 gene is the cell surface docking receptor for latent TGFβ, which is expressed naturally by platelets and regulatory T cells (Treg). Although Lrrc32 is amplified frequently in breast cancer, the expression and relevant functions of GARP in cancer have not been explored. Here, we report that GARP exerts oncogenic effects, promoting immune tolerance by enriching and activating latent TGFβ in the tumor microenvironment. We found that human breast, lung, and colon cancers expressed GARP aberrantly. In genetic studies in normal mammary gland epithelial and carcinoma cells, GARP expression increased TGFβ bioactivity and promoted malignant transformation in immunodeficient mice. In breast carcinoma-bearing mice that were immunocompetent, GARP overexpression promoted Foxp3⁺ Treg activity, which in turn contributed to enhancing cancer progression and metastasis. Notably, administration of a GARP-specific mAb limited metastasis in an orthotopic model of human breast cancer. Overall, these results define the oncogenic effects of the GARP-TGFβ axis in the tumor microenvironment and suggest mechanisms that might be exploited for diagnostic and therapeutic purposes. Cancer Res; 76(24); 7106-17. ©2016 AACR.

Mechanisms of TGFβ-Induced Epithelial-Mesenchymal Transition

Transitory phenotypic changes such as the epithelial–mesenchymal transition (EMT) help embryonic cells to generate migratory descendants that populate new sites and establish the distinct tissues in the developing embryo. The mesenchymal descendants of diverse epithelia also participate in the wound healing response of adult tissues, and facilitate the progression of cancer. EMT can be induced by several extracellular cues in the microenvironment of a given epithelial tissue. One such cue, transforming growth factor β (TGFβ), prominently induces EMT via a group of specific transcription factors. The potency of TGFβ is partly based on its ability to perform two parallel molecular functions, i.e. to induce the expression of growth factors, cytokines and chemokines, which sequentially and in a complementary manner help to establish and maintain the EMT, and to mediate signaling crosstalk with other developmental signaling pathways, thus promoting changes in cell differentiation. The molecules that are activated by TGFβ signaling or act as cooperating partners of this pathway are impossible to exhaust within a single coherent and contemporary report. Here, we present selected examples to illustrate the key principles of the circuits that control EMT under the influence of TGFβ.