NF-κB represses retinoic acid receptor-mediated GPRC5A transactivation in lung epithelial cells to promote neoplasia

Chronic inflammation is associated with lung tumorigenesis, in which NF-κB-mediated epigenetic regulation plays a critical role. Lung tumor suppressor G protein-coupled receptor, family C, member 5A (GPRC5A), is repressed in most non-small cell lung cancer (NSCLC); however, the mechanisms remain unclear. Here, we show that NF-κB acts as a transcriptional repressor in suppression of GPRC5A. NF-κB induced GPRC5A repression both in vitro and in vivo. Intriguingly, transactivation of NF-κB downstream targets was not required, but the transactivation domain of RelA/p65 was required for GPRC5A repression. NF-κB did not bind to any potential cis-element in the GPRC5A promoter. Instead, p65 was complexed with retinoic acid receptor α/β (RARα/β) and recruited to the RA response element site at the GPRC5A promoter, resulting in disrupted RNA polymerase II complexing and suppressed transcription. Notably, phosphorylation on serine 276 of p65 was required for interaction with RARα/β and repression of GPRC5A. Moreover, NF-κB-mediated epigenetic repression was through suppression of acetylated histone H3K9 (H3K9ac), but not DNA methylation of the CpG islands, at the GPRC5A promoter. Consistently, a histone deacetylase inhibitor, but not DNA methylation inhibitor, restored GPRC5A expression in NSCLC cells. Thus, NF-κB induces transcriptional repression of GPRC5A via a complex with RARα/β and mediates epigenetic repression via suppression of H3K9ac.

The Context-Dependent Impact of Integrin-Associated CD151 and Other Tetraspanins on Cancer Development and Progression: A Class of Versatile Mediators of Cellular Function and Signaling, Tumorigenesis and Metastasis

Simple Summary

Tetraspanins are a family of molecules abundantly expressed on the surface of normal or tumor cells. They have been implicated in recruiting or sequestering key molecular regulators of malignancy of a variety of human cancers, including breast and lung cancers, glioblastoma and leukemia. Yet, how their actions take place remains mysterious due to a lack of traditional platform for molecular interactions. The current review digs into this mystery by examining findings from recent studies of multiple tetraspanins, particularly CD151. The molecular basis for differential impact of tetraspanins on tumor development, progression, and spreading to secondary sites is highlighted, and the complexity and plasticity of their control over tumor cell activities and interaction with their surroundings is discussed. Finally, an outlook is provided regarding tetraspanins as candidate biomarkers and targets for the diagnosis and treatment of human cancer.

Abstract

As a family of integral membrane proteins, tetraspanins have been functionally linked to a wide spectrum of human cancers, ranging from breast, colon, lung, ovarian, prostate, and skin carcinomas to glioblastoma. CD151 is one such prominent member of the tetraspanin family recently suggested to mediate tumor development, growth, and progression in oncogenic context- and cell lineage-dependent manners. In the current review, we summarize recent advances in mechanistic understanding of the function and signaling of integrin-associated CD151 and other tetraspanins in multiple cancer types. We also highlight emerging genetic and epigenetic evidence on the intrinsic links between tetraspanins, the epithelial-mesenchymal transition (EMT), cancer stem cells (CSCs), and the Wnt/β-catenin pathway, as well as the dynamics of exosome and cellular metabolism. Finally, we discuss the implications of the highly plastic nature and epigenetic susceptibility of CD151 expression, function, and signaling for clinical diagnosis and therapeutic intervention for human cancer.

Dysregulated Glutamate Transporter SLC1A1 Propels Cystine Uptake via Xc- for Glutathione Synthesis in Lung Cancer

Cancer cells need to generate large amounts of glutathione (GSH) to buffer oxidative stress during tumor development. A rate-limiting step for GSH biosynthesis is cystine uptake via a cystine/glutamate antiporter Xc^-. Xc^- is a sodium-independent antiporter passively driven by concentration gradients from extracellular cystine and intracellular glutamate across the cell membrane. Increased uptake of cystine via Xc^- in cancer cells increases the level of extracellular glutamate, which would subsequently restrain cystine uptake via Xc^-. Cancer cells must therefore evolve a mechanism to overcome this negative feedback regulation. In this study, we report that glutamate transporters, in particular SLC1A1, are tightly intertwined with cystine uptake and GSH biosynthesis in lung cancer cells. Dysregulated SLC1A1, a sodium-dependent glutamate carrier, actively recycled extracellular glutamate into cells, which enhanced the efficiency of cystine uptake via Xc^- and GSH biosynthesis as measured by stable isotope-assisted metabolomics. Conversely, depletion of glutamate transporter SLC1A1 increased extracellular glutamate, which inhibited cystine uptake, blocked GSH synthesis, and induced oxidative stress-mediated cell death or growth inhibition. Moreover, glutamate transporters were frequently upregulated in tissue samples of patients with non-small cell lung cancer. Taken together, active uptake of glutamate via SLC1A1 propels cystine uptake via Xc^- for GSH biosynthesis in lung tumorigenesis. SIGNIFICANCE: Cellular GSH in cancer cells is not only determined by upregulated Xc^- but also by dysregulated glutamate transporters, which provide additional targets for therapeutic intervention.

Guidelines and definitions for research on epithelial-mesenchymal transition

Epithelial–mesenchymal transition (EMT) encompasses dynamic changes in cellular organization from epithelial to mesenchymal phenotypes, which leads to functional changes in cell migration and invasion. EMT occurs in a diverse range of physiological and pathological conditions and is driven by a conserved set of inducing signals, transcriptional regulators and downstream effectors. With over 5,700 publications indexed by Web of Science in 2019 alone, research on EMT is expanding rapidly. This growing interest warrants the need for a consensus among researchers when referring to and undertaking research on EMT. This Consensus Statement, mediated by ‘the EMT International Association’ (TEMTIA), is the outcome of a 2-year-long discussion among EMT researchers and aims to both clarify the nomenclature and provide definitions and guidelines for EMT research in future publications. We trust that these guidelines will help to reduce misunderstanding and misinterpretation of research data generated in various experimental models and to promote cross-disciplinary collaboration to identify and address key open questions in this research field. While recognizing the importance of maintaining diversity in experimental approaches and conceptual frameworks, we emphasize that lasting contributions of EMT research to increasing our understanding of developmental processes and combatting cancer and other diseases depend on the adoption of a unified terminology to describe EMT.

In this Consensus Statement, the authors (on behalf of the EMT International Association) propose guidelines to define epithelial–mesenchymal transition, its phenotypic plasticity and the associated multiple intermediate epithelial–mesenchymal cell states. Clarification of nomenclature and definitions will help reduce misinterpretation of research data generated in different experimental model systems and promote cross-disciplinary collaboration.

Integrin-associated CD151 is a suppressor of prostate cancer progression

Owing to the complexity of interacting molecular networks on the cell surface, integrin-associated tetraspanin CD151 remains controversial regarding its clinical importance and functional impact in prostate cancer. The current study evaluated dynamics and clinical importance of CD151 expression and its function in prostate cancer by IHC analysis of two independent patient cohorts (n=80, 181), bioinformatic interrogation of the TCGA database, and evaluation of gene knockdown effect at the cellular level. Our data showed that aside from high mRNA expression, CD151 was primarily localized to intercellular junctions at the plasma membrane in normal prostate glands or benign tissues, regardless of nature of antibodies used. By contrast, in primary tumors from patients with metastatic disease, CD151 was largely localized in the cytosol. Furthermore, the level of the cell-cell junction-linked CD151 was inversely associated with Gleason grade and tumor stage (P<0.001 for both). The portion of primary tumors expressing junctional CD151 was also three-fold less in the metastatic patient population than its counterpart (P<0.001). In line with these observations, CD151 and its associated α3β1 or α6β4 integrin inversely correlated with androgen receptor (AR) at the mRNA level (Spearman coefficient: -0.44, -0.48 and -0.42) in the TCGA cohort. Expression of these adhesion molecules also correlated with DNA methylation in their promoters (Spearman coefficient: -0.37, -0.71 and -0.82). Combined, these data suggest that CD151 and associated integrins are linked to tumor metastasis through AR and the epigenetic program. Meanwhile, CD151 knockdown in E-cadherin-positive tumor cells led to increased cell proliferation and induction of the epithelial-mesenchymal transition (EMT)-like phenotype. Given the strong RGD-binding integrin dependence of EMT-featured tumor cells, we examined focal adhesion kinase (FAK), their key signaling effector, in the above patient cohorts. In contrast to CD151, FAK exhibited positive correlation with tumor grade and stage as well as AR and p53 inactivation at either mRNA, protein or genomic level. Taken together, our results suggest that CD151 represses prostate cancer by antagonizing cell proliferation, EMT and the signaling of RGD-binding integrins. Since this anti-tumorigenic role is prone to the AR-mediated transcriptional and epigenetic regulation, CD151 and possibly α3β1 and α6β4 integrins are of potential biomarkers for metastatic prostate cancer.

PTGES/PGE2 signaling links immunosuppression and lung metastasis in Gprc5a-knockout mouse model

Chronic inflammation has been linked to promotion of tumorigenesis and metastasis in lung. However, due to lack of a relevant animal model for characterization, the underlying mechanism remains elusive. Lung tumor suppressor gene Gprc5a-knockout (ko) mice are susceptible to lung inflammation, tumorigenesis and metastasis, which resembles the pathological features in human patients. Here, we showed that PTGES/PGE2 signaling was highly associated with lung tumorigenesis and metastasis in Gprc5a-ko mice. Interestingly, Ptges-knockout in mouse lung tumor cells, although reduced their stemness and EMT-like features, still formed tumors and lung metastasis in immune-deficient nude mice, but not in immune-competent mice. This suggests that the major role of PTGES/PGE2 signaling in tumorigenicity and lung metastasis is through immunosuppression. Mechanistically, PTGES/PGE2 signaling intrinsically endows tumor cells resistant to T-cell cytotoxicity, and induces cytokines extrinsically for MDSC recruitment, which is crucial for suppression of T-cell immunity. Importantly, targeting PGE2 signaling in Gprc5a-ko mice by PTGES inhibitor suppressed MDSC recruitment, restored T cells, and significantly repressed lung metastasis. Thus, PTGES/PGE2 signaling links immunosuppression and metastasis in an inflammatory lung microenvironment of Gprc5a-ko mouse model.

Hsp47 promotes cancer metastasis by enhancing collagen-dependent cancer cell-platelet interaction

Increased expression of extracellular matrix (ECM) proteins in circulating tumor cells (CTCs) suggests potential function of cancer cell-produced ECM in initiation of cancer cell colonization. Here, we showed that collagen and heat shock protein 47 (Hsp47), a chaperone facilitating collagen secretion and deposition, were highly expressed during the epithelial-mesenchymal transition (EMT) and in CTCs. Hsp47 expression induced mesenchymal phenotypes in mammary epithelial cells (MECs), enhanced platelet recruitment, and promoted lung retention and colonization of cancer cells. Platelet depletion in vivo abolished Hsp47-induced cancer cell retention in the lung, suggesting that Hsp47 promotes cancer cell colonization by enhancing cancer cell-platelet interaction. Using rescue experiments and functional blocking antibodies, we identified type I collagen as the key mediator of Hsp47-induced cancer cell-platelet interaction. We also found that Hsp47-dependent collagen deposition and platelet recruitment facilitated cancer cell clustering and extravasation in vitro. By analyzing DNA/RNA sequencing data generated from human breast cancer tissues, we showed that gene amplification and increased expression of Hsp47 were associated with cancer metastasis. These results suggest that targeting the Hsp47/collagen axis is a promising strategy to block cancer cell-platelet interaction and cancer colonization in secondary organs.

BRD4 modulates vulnerability of triple-negative breast cancer to targeting of integrin-dependent signaling pathways

PURPOSE

Stemming from a myriad of genetic and epigenetic alterations, triple-negative breast cancer (TNBC) is tied to poor clinical outcomes and aspires for individualized therapies. Here we investigated the therapeutic potential of co-inhibiting integrin-dependent signaling pathway and BRD4, a transcriptional and epigenetic mediator, for TNBC.

METHODS

Two independent patient cohorts were subjected to bioinformatic and IHC examination for clinical association of candidate cancer drivers. The efficacy and biological bases for co-targeting these drivers were interrogated using cancer cell lines, a protein kinase array, chemical inhibitors, RNAi/CRISPR/Cas9 approaches, and a 4 T1-Balb/c xenograft model.

RESULTS

We found that amplification of the chromosome 8q24 region occurred in nearly 20% of TNBC tumors, and that it coincided with co-upregulation or amplification of c-Myc and FAK, a key effector of integrin-dependent signaling. This co-upregulation at the mRNA or protein level correlated with a poor patient survival (p < 0.0109 or p < 0.0402, respectively). Furthermore, we found that 14 TNBC cell lines exhibited high vulnerabilities to the combination of JQ1 and VS-6063, potent pharmacological antagonists of the BRD4/c-Myc and integrin/FAK-dependent pathways, respectively. We also observed a cooperative inhibitory effect of JQ1 and VS-6063 on tumor growth and infiltration of Ly6G⁺ myeloid-derived suppressor cells in vivo. Finally, we found that JQ1 and VS-6063 cooperatively induced apoptotic cell death by altering XIAP, Bcl2/Bcl-xl and Bim levels, impairing c-Src/p130Cas-, PI3K/Akt- and RelA-associated signaling, and were linked to EMT-inducing transcription factor Snail- and Slug-dependent regulation.

CONCLUSION

Based on our results, we conclude that the BRD4/c-Myc- and integrin/FAK-dependent pathways act in concert to promote breast cancer cell survival and poor clinical outcomes. As such, they represent promising targets for a synthetic lethal-type of therapy against TNBC.

Deletion of tetraspanin CD151 alters the Wnt oncogene-induced mammary tumorigenesis: A cell type-linked function and signaling

Tetraspanin CD151 is increasingly implicated as a multifaceted mediator of cancer development and progression. Here we investigated the role of CD151 in breast cancer in the context of the Wnt oncogenic activation. Our data showed that removal of one or both of CD151 alleles in the MMTV-Wnt1 model significantly decreased the tumor-free survival of mice from 34 weeks on average to 22 weeks and 18 weeks, respectively. This effect coincided with an accelerated tumor growth and an increased number of Ki-67⁺ proliferative cells. Mechanistically, the CD151-deficient tumors were largely ER⁺, and exhibited hyperactivation of the Wnt pathway as reflected by a marked upregulation in β-catenin and Cyclin D1, and their target genes. In addition, E-cadherin displayed a cytosolic distribution and transcription factor Snail was markedly upregulated. Collectively, this data implies that CD151 suppresses the Wnt1-driven tumorigenesis, at least in part, via counteracting the epithelial-mesenchymal transition (EMT)-like program in luminal epithelial cells. Meanwhile, the proportion of tumor cells expressing CK5 or p63, the biomarkers of myoepithelial/basal cells, markedly decreased in the absence of CD151. This change was accompanied by a decreased invasiveness of tumors and their incompetence to form a long-term cell culture. Consistent with this basal cell-linked role, the CD151 downregulation impairs mammosphere formation in MCF-10A cells and the defect was rescued by re-expression of intact CD151 ORF, but not its integrin binding-defective mutant. Overall, our study suggests that CD151 is a key player in the Wnt oncogene-driven tumorigenesis and impacts breast cancer malignancy in a cell type-dependent manner.

Oncometabolite modification of Keap1 links GSTZ1 deficiency with cancer

Metabolic abnormalities are emerging as an active driver to the development, progression and metastasis of various tumors. In the recent issue of the EMBO Journal, Yang and colleagues identified that succinylacetone (SA) could act as an oncometabolite and that accumulation of SA activates the NRF2/IGF1R axis in hepatocellular carcinoma (HCC) development. These discoveries not only yield great insights in the understanding of tumor biology, but also hold significant clinical ramifications, as these findings may pave a new way for the early diagnosis and treatment of HCC.

Metabolic reprogram associated with epithelial-mesenchymal transition in tumor progression and metastasis

Epithelial-mesenchymal Transition (EMT) is a de-differentiation program that imparts tumor cells with the phenotypic and cellular plasticity required for drug resistance, metastasis, and recurrence. This dynamic and reversible events is governed by a network of EMT-transcription factors (EMT-TFs) through epigenetic regulation. Many chromatin modifying-enzymes utilize metabolic intermediates as cofactors or substrates; this suggests that EMT is subjected to the metabolic regulation. Conversely, EMT rewires metabolic program to accommodate cellular changes during EMT. Here we summarize the latest findings regarding the epigenetic regulation of EMT, and discuss the mutual interactions among metabolism, epigenetic regulation, and EMT. Finally, we provide perspectives of how this interplay contributes to cellular plasticity, which may result in the clinical manifestation of tumor heterogeneity.

ITCH nuclear translocation and H1.2 polyubiquitination negatively regulate the DNA damage response

The downregulation of the DNA damage response (DDR) enables aggressive tumors to achieve uncontrolled proliferation against replication stress, but the mechanisms underlying this process in tumors are relatively complex. Here, we demonstrate a mechanism through which a distinct E3 ubiquitin ligase, ITCH, modulates DDR machinery in triple-negative breast cancer (TNBC). We found that expression of a nuclear form of ITCH was significantly increased in human TNBC cell lines and tumor specimens. Phosphorylation of ITCH at Ser257 by AKT led to the nuclear localization of ITCH and ubiquitination of H1.2. The ITCH-mediated polyubiquitination of H1.2 suppressed RNF8/RNF168-dependent formation of 53BP1 foci, which plays important roles in DDR. Consistent with these findings, impaired ITCH nuclear translocation and H1.2 polyubiquitination sensitized cells to replication stress and limited cell growth and migration. AKT activation of ITCH-H1.2 axis may confer TNBC cells with a DDR repression to counteract the replication stress and increase cancer cell survivorship and growth potential.

Stabilization of PTGES by deubiquitinase USP9X promotes metastatic features of lung cancer via PGE2 signaling

Early metastasis and local recurrence are the major causes of mortality and poor prognosis of non-small cell lung cancer (NSCLC). However, the underlying mechanisms of these processes are poorly understood. In this study, we aimed to investigate the roles of the PTGES/PGE2 pathway in lung cancer progression. We found that prostaglandin E synthase (PTGES), a key enzyme for PGE2 synthesis in the arachidonic acid pathway, was highly dysregulated in NSCLC. Dysregulated PTGES was essential for the promotion of tumor migration and metastasis of NSCLC cells. Knockdown of PTGES in lung cancer cells resulted in suppressed cell migration, which was reversed by exogenous PGE2. Consistent with this, PTGES knockdown also reduced the expression of CSC markers, tumor sphere formation, colony forming activity, tumorigenicity, and lung metastasis in vivo. Dysregulated PTGES is mainly attributed to protein stabilization by USP9X, a deubiquitination enzyme. USP9X physically interacted with PTGES and prevented it from proteasome-directed degradation via deubiquitination. Consistent with this, USP9X expression was highly correlated with PTGES expression in NSCLC tumor tissues. Taken together, our results show that the upregulated USP9X-PTGES-PGE2 axis contributes significantly to the metastatic features of NSCLC.

Stress-induced epinephrine enhances lactate dehydrogenase A and promotes breast cancer stem-like cells

Chronic stress triggers activation of the sympathetic nervous system and drives malignancy. Using an immunodeficient murine system, we showed that chronic stress-induced epinephrine promoted breast cancer stem-like properties via lactate dehydrogenase A-dependent (LDHA-dependent) metabolic rewiring. Chronic stress-induced epinephrine activated LDHA to generate lactate, and the adjusted pH directed USP28-mediated deubiquitination and stabilization of MYC. The SLUG promoter was then activated by MYC, which promoted development of breast cancer stem-like traits. Using a drug screen that targeted LDHA, we found that a chronic stress-induced cancer stem-like phenotype could be reversed by vitamin C. These findings demonstrated the critical importance of psychological factors in promoting stem-like properties in breast cancer cells. Thus, the LDHA-lowering agent vitamin C can be a potential approach for combating stress-associated breast cancer.

Targeting the BRD4/FOXO3a/CDK6 axis sensitizes AKT inhibition in luminal breast cancer

BRD4 assembles transcriptional machinery at gene super-enhancer regions and governs the expression of genes that are critical for cancer progression. However, it remains unclear whether BRD4-mediated gene transcription is required for tumor cells to develop drug resistance. Our data show that prolonged treatment of luminal breast cancer cells with AKT inhibitors induces FOXO3a dephosphorylation, nuclear translocation, and disrupts its association with SirT6, eventually leading to FOXO3a acetylation as well as BRD4 recognition. Acetylated FOXO3a recognizes the BD2 domain of BRD4, recruits the BRD4/RNAPII complex to the CDK6 gene promoter, and induces its transcription. Pharmacological inhibition of either BRD4/FOXO3a association or CDK6 significantly overcomes the resistance of luminal breast cancer cells to AKT inhibitors in vitro and in vivo. Our study reports the involvement of BRD4/FOXO3a/CDK6 axis in AKTi resistance and provides potential therapeutic strategies for treating resistant breast cancer.

Twist promotes tumor metastasis in basal-like breast cancer by transcriptionally upregulating ROR1

Rationale: Twist is a key transcription factor for induction of epithelial-mesenchymal transition (EMT), which promotes cell migration, invasion, and cancer metastasis, confers cancer cells with stem cell-like characteristics, and provides therapeutic resistance. However, the functional roles and targeted genes of Twist in EMT and cancer progression remain elusive. Methods: The potential targeted genes of Twist were identified from the global transcriptomes of T47D/Twist cells by microarray analysis. EMT phenotype was detected by western blotting and immunofluorescence of marker proteins. The dual-luciferase reporter and chromatin immunoprecipitation assays were employed to observe the direct transcriptional induction of ROR1 by Twist. A lung metastasis model was used to study the pro-metastatic role of Twist and ROR1 by injecting MDA-MB-231 cells into tail vein of nude mice. Bio-informatics analysis was utilized to measure the metastasis-free survival of breast cancer patients. Results: Twist protein was proved to directly activate the transcription of ROR1 gene, a receptor of Wnt5a in non-canonical WNT signaling pathway. Silencing of ROR1 inhibited EMT process, cell migration, invasion, and cancer metastasis of basal-like breast cancer (BLBC) cells. Knockdown of ROR1 also ameliorated the pro-metastatic effect of Twist. Furthermore, analyses of clinical specimens indicated that high expression of both ROR1 and Twist tightly correlates with poor metastasis-free survival of breast cancer patients. Conclusion: ROR1 is a targeted gene of Twist. Twist/ROR1 signaling is critical for invasion and metastasis of BLBC cells.

FH535, a β-catenin pathway inhibitor, represses pancreatic cancer xenograft growth and angiogenesis

The WNT/β-catenin pathway plays an important role in pancreatic cancer carcinogenesis. We evaluated the correlation between aberrant β-catenin pathway activation and the prognosis pancreatic cancer, and the potential of applying the β-catenin pathway inhibitor FH535 to pancreatic cancer treatment. Meta-analysis and immunohistochemistry showed that abnormal β-catenin pathway activation was associated with unfavorable outcome. FH535 repressed pancreatic cancer xenograft growth in vivo. Gene Ontology (GO) analysis of microarray data indicated that target genes responding to FH535 participated in stemness maintenance. Real-time PCR and flow cytometry confirmed that FH535 downregulated CD24 and CD44, pancreatic cancer stem cell (CSC) markers, suggesting FH535 impairs pancreatic CSC stemness. GO analysis of β-catenin chromatin immunoprecipitation sequencing data identified angiogenesis-related gene regulation. Immunohistochemistry showed that higher microvessel density correlated with elevated nuclear β-catenin expression and unfavorable outcome. FH535 repressed the secretion of the proangiogenic cytokines vascular endothelial growth factor (VEGF), interleukin (IL)-6, IL-8, and tumor necrosis factor-α, and also inhibited angiogenesis in vitro and in vivo. Protein and mRNA microarrays revealed that FH535 downregulated the proangiogenic genes ANGPT2, VEGFR3, IFN-γ, PLAUR, THPO, TIMP1, and VEGF. FH535 not only represses pancreatic CSC stemness in vitro, but also remodels the tumor microenvironment by repressing angiogenesis, warranting further clinical investigation.

Snail determines the therapeutic response to mTOR kinase inhibitors by transcriptional repression of 4E-BP1

Loss of 4E-BP1 expression has been linked to cancer progression and resistance to mTOR inhibitors, but the mechanism underlying 4E-BP1 downregulation in tumors remains unclear. Here we identify Snail as a strong transcriptional repressor of 4E-BP1. We find that 4E-BP1 expression inversely correlates with Snail level in cancer cell lines and clinical specimens. Snail binds to three E-boxes present in the human 4E-BP1 promoter to repress transcription of 4E-BP1. Ectopic expression of Snail in cancer cell lines lacking Snail profoundly represses 4E-BP1 expression, promotes cap-dependent translation in polysomes, and reduces the anti-proliferative effect of mTOR kinase inhibitors. Conversely, genetic and pharmacological inhibition of Snail function restores 4E-BP1 expression and sensitizes cancer cells to mTOR kinase inhibitors by enhancing 4E-BP1-mediated translation-repressive effect on cell proliferation and tumor growth. Our study reveals a critical Snail-4E-BP1 signaling axis in tumorigenesis, and provides a rationale for targeting Snail to improve mTOR-targeted therapies.

4E-BP1 is a translational repressor critical in mTOR signaling, whereas Snail is a critical promoter of epithelial to mesenchymal transition. Here the authors show that Snail induces resistance to mTOR inhibitors by repressing 4E-BP1 expression and promoting cell cycle progression via upregulating cycD.

Nanoparticle Delivery of miR-34a Eradicates Long-term-cultured Breast Cancer Stem Cells via Targeting C22ORF28 Directly

Rationale: Cancer stem cells (CSCs) have been implicated as the seeds of therapeutic resistance and metastasis, due to their unique abilities of self-renew, wide differentiation potentials and resistance to most conventional therapies. It is a proactive strategy for cancer therapy to eradicate CSCs. Methods: Tumor tissue-derived breast CSCs (BCSC), including XM322 and XM607, were isolated by fluorescence-activated cell sorting (FACS); while cell line-derived BCSC, including MDA-MB-231.SC and MCF-7.SC, were purified by magnetic-activated cell sorting (MACS). Analyses of microRNA and mRNA expression array profiles were performed in multiple breast cell lines. The mentioned nanoparticles were constructed following the standard molecular cloning protocol. Tissue microarray analysis has been used to study 217 cases of clinical breast cancer specimens. Results: Here, we have successfully established four long-term maintenance BCSC that retain their tumor-initiating biological properties. Our analyses of microarray and qRT-PCR explored that miR-34a is the most pronounced microRNA for investigation of BCSC. We establish hTERT promoter-driven VISA delivery of miR-34a (TV-miR-34a) plasmid that can induce high throughput of miR-34a expression in BCSC. TV-miR-34a significantly inhibited the tumor-initiating properties of long-term-cultured BCSC in vitro and reduced the proliferation of BCSC in vivo by an efficient and safe way. TV-miR-34a synergizes with docetaxel, a standard therapy for invasive breast cancer, to act as a BCSC inhibitor. Further mechanistic investigation indicates that TV-miR-34a directly prevents C22ORF28 accumulation, which abrogates clonogenicity and tumor growth and correlates with low miR-34 and high C22ORF28 levels in breast cancer patients. Conclusion: Taken together, we generated four long-term maintenance BCSC derived from either clinical specimens or cell lines, which would be greatly beneficial to the research progress in breast cancer patients. We further developed the non-viral TV-miR-34a plasmid, which has a great potential to be applied as a clinical application for breast cancer therapy.

Stabilization of the transcription factors slug and twist by the deubiquitinase dub3 is a key requirement for tumor metastasis

The epithelial-mesenchymal transition (EMT) represents a cellular de-differentiation process that provides cells with the increased plasticity required during embryonic development, tissue remodeling, wound healing and metastasis. Slug and Twist are two key EMT transcription factors (EMT-TFs) that are tightly regulated via ubiquitination and degradation. How Slug and Twist escape degradation and become stabilized in cancer cells remains unclear. One plausible mechanism of Slug and Twist stabilization involves removal of ubiquitin by deubiquitinases (DUBs). In this study, we identified Dub3 as a novel DUB for both Slug and Twist. We further found that Dub3 overexpression increased Slug and Twist protein levels in a dose-dependent manner, whereas Dub3-knockdown decreased their protein levels. Of importance, Dub3 interacted with Slug and Twist and prevented them from degradation, thereby promoting migration, invasion, and cancer stem cell (CSC)-like properties of breast cancer cells. Intriguingly, Dub3 was identified as an early response gene that was upregulated after exposure to inflammatory cytokines such as IL-6, which plays a critical role in the growth and metastasis of breast cancer cells, as well as the maintenance of breast CSCs. We found that Dub3 played an essential role in IL-6 induced EMT through stabilization of Slug and Twist. Our study has uncovered an IL-6-Dub3-Slug/Twist signaling axis during EMT and suggests potential approaches that could target Dub3 to prevent metastatic breast tumor.

The Role of Tumor Associated Macrophages in the Tumor Microenvironment: Mechanism and Functions

During tumor progression, several types of inflammatory cells are recruited into the tumor site, where they participate in tumor-associated inflammation, such as fibroblasts, granulocytes, lymphocytes and macrophages. Macrophages infiltrating into the tumor microenvironment are termed tumorassociated macrophages (TAMs). In response to multiple stimuli, macrophages undergo recruitment and polarization, and play an important role in further tumor development. In this article, we present a review of the mechanism of macrophage' recruitment, and the role that TAMs play in promoting immunosuppression, tumor progress and metastasis, as well as chemoresistance and future therapeutic strategies.

The Role of Stromal Components in Pancreatic Cancer Progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human cancers, and is known for its extremely poor prognosis. Because of the location and composition of the organ, early symptoms cannot be visualized as easily as in other solid tumors. In the past decades, researchers have been mostly working on the genetic and epigenetic alterations of the cancer cells themselves, and therapies on pancreatic cancer cells alone have failed to significantly improve patient outcome. With the identification of abundant tumor stromal responses, the focus of pancreatic cancer research has begun to change. Increasing evidence has proved that the tumor stroma, especially the cell components (such as pancreatic stellate cells, tumor-associated macrophages, mast cells etc.) plays a key role in the development of PDAC. In this review, we discuss the interactions between cancer cells and several important cell components of the tumor stroma, as well their role in tumor growth, migration, invasion, angiogenesis and immune recognition.

POMC maintains tumor-initiating properties of tumor tissue-derived long-term-cultured breast cancer stem cells

The identification and understanding of the molecular network of cancer stem cells (CSCs) have had a profound impact on our view of carcinogenesis and treatment strategy. Unfortunately, a major problem is that serial passages of CSCs from clinical solid tumor specimens currently are not available in any lab, and thus, reported data are difficult to confirm and intensively interrogated. Here, we have generated two tumor tissue-derived breast CSC (BCSC) lines that showed prolonged maintenance over 20 serial passages in vitro, while retaining their tumor-initiating biological properties. We then deciphered the intrinsic mechanism using analyses of mRNA expression array profiles. It has been determined that pro-opiomelanocortin (POMC) is closely related with protein phosphorylation mediated by G-protein-coupled estrogen receptor (GPER) in BCSC. Following, knockdown of POMC inhibits properties of mammosphere formation, CD44⁺ CD24^- population, CD44 expression, and clonogenicity ability in BCSC. We found that inhibition of POMC attenuates phosphorylation of AKT2 and GSK3β in BCSC. Further in vivo investigations demonstrated that POMC interference regulates proliferation of BCSC-bearing tumors. Combination of the clinical results that POMC positive expression is frequently upregulated in human breast cancer and POMC positivity correlated with a poor prognosis, POMC is a potential therapeutic target for BCSC. In conclusion, we have successfully established two long-term-cultured BCSC from clinical specimens. We further indicated that POMC acts as a potential therapeutic target and prognostic marker for future treatment of BCSC.

Dub3 inhibition suppresses breast cancer invasion and metastasis by promoting Snail1 degradation

Snail1, a key transcription factor of epithelial-mesenchymal transition (EMT), is subjected to ubiquitination and degradation, but the mechanism by which Snail1 is stabilized in tumours remains unclear. We identify Dub3 as a bona fide Snail1 deubiquitinase, which interacts with and stabilizes Snail1. Dub3 is overexpressed in breast cancer; knockdown of Dub3 resulted in Snail1 destabilization, suppressed EMT and decreased tumour cell migration, invasion, and metastasis. These effects are rescued by ectopic Snail1 expression. IL-6 also stabilizes Snail1 by inducing Dub3 expression, the specific inhibitor WP1130 binds to Dub3 and inhibits the Dub3-mediating Snail1 stabilization in vitro and in vivo. Our study reveals a critical Dub3-Snail1 signalling axis in EMT and metastasis, and provides an effective therapeutic approach against breast cancer.

Inhibition of the integrin/FAK signaling axis and c-Myc synergistically disrupts ovarian cancer malignancy

Integrins, a family of heterodimeric receptors for extracellular matrix, are promising therapeutic targets for ovarian cancer, particularly high-grade serous-type (HGSOC), as they drive tumor cell attachment, migration, proliferation and survival by activating focal adhesion kinase (FAK)-dependent signaling. Owing to the potential off-target effects of FAK inhibitors, disruption of the integrin signaling axis remains to be a challenge. Here, we tackled this barrier by screening for inhibitors being functionally cooperative with small-molecule VS-6063, a phase II FAK inhibitor. From this screening, JQ1, a potent inhibitor of Myc oncogenic network, emerged as the most robust collaborator. Treatment with a combination of VS-6063 and JQ1 synergistically caused an arrest of tumor cells at the G2/M phase and a decrease in the XIAP-linked cell survival. Our subsequent mechanistic analyses indicate that this functional cooperation was strongly associated with the concomitant disruption of activation or expression of FAK and c-Myc as well as their downstream signaling through the PI3K/Akt pathway. In line with these observations, we detected a strong co-amplification or upregulation at genomic or protein level for FAK and c-Myc in a large portion of primary tumors in the TCGA or a local HGSOC patient cohort. Taken together, our results suggest that the integrin–FAK signaling axis and c-Myc synergistically drive cell proliferation, survival and oncogenic potential in HGSOC. As such, our study provides key genetic, functional and signaling bases for the small-molecule-based co-targeting of these two distinct oncogenic drivers as a new line of targeted therapy against human ovarian cancer.

The regulation of snail: on the ubiquitin edge

Metastasis accounts for a majority of cancer death. One key feature during metastasis is epithelial-mesenchymal transition (EMT), which is regulated by transcription factors such as Snail and Twist. In non-malignant cells, Snail has a short half-life and is degraded via ubiquitination, but its stability is increased in cancer cell. However, the mechanism by which Snail escapes ubiquitination and degradation remains unknown. Recently, we found that Dub3 is a deubiquinase of Snail. Most importantly, we determined that Dub3 responded to extracellular signals such as IL-6, and that the resultant signaling prevented Snail degradation, and promoted cancer growth, invasion, and migration. In this highlight, we present a concise picture of how the transcription factor Snail is regulated by ubiquitination in cancer cells, the role of Dub3 in this process, and its potential use as a treatment target.

Inflammatory stimuli promote growth and invasion of pancreatic cancer cells through NF-κB pathway dependent repression of PP2Ac

Previous studies have indicated that inflammatory stimulation represses protein phosphatase 2A (PP2A), a well-known tumor suppressor. However, whether PP2A repression participates in pancreatic cancer progression has not been verified. We used lipopolysaccharide (LPS) and macrophage-conditioned medium (MCM) to establish in vitro inflammation models, and investigated whether inflammatory stimuli affect pancreatic cancer cell growth and invasion PP2A catalytic subunit (PP2Ac)-dependently. Via nude mouse models of orthotopic tumor xenografts and dibutyltin dichloride (DBTC)-induced chronic pancreatitis, we evaluated the effect of an inflammatory microenvironment on PP2Ac expression in vivo. We cloned the PP2Acα and PP2Acβ isoform promoters to investigate the PP2Ac transcriptional regulation mechanisms. MCM accelerated pancreatic cancer cell growth; MCM and LPS promoted cell invasion. DBTC promoted xenograft growth and metastasis, induced tumor-associated macrophage infiltration, promoted angiogenesis, activated the nuclear factor-κB (NF-κB) pathway, and repressed PP2Ac expression. In vitro, LPS and MCM downregulated PP2Ac mRNA and protein. PP2Acα overexpression attenuated JNK, ERK, PKC, and IKK phosphorylation, and impaired LPS/MCM-stimulated cell invasion and MCM-promoted cell growth. LPS and MCM activated the NF-κB pathway in vitro. LPS and MCM induced IKK and IκB phosphorylation, leading to p65/RelA nuclear translocation and transcriptional activation. Overexpression of the dominant negative forms of IKKα attenuated LPS and MCM downregulation of PP2Ac, suggesting inflammatory stimuli repress PP2Ac expression NF-κB pathway-dependently. Luciferase reporter gene assay verified that LPS and MCM downregulated PP2Ac transcription through an NF-κB-dependent pathway. Our study presents a new mechanism in inflammation-driven cancer progression through NF-κB pathway-dependent PP2Ac repression.

Epithelial neoplasia coincides with exacerbated injury and fibrotic response in the lungs of Gprc5a-knockout mice following silica exposure

Exposure to crystalline silica is suggested to increase the risk for a variety of lung diseases, including fibrosis and lung cancer. However, epidemiological evidences for the exposure-risk relationship are ambiguous and conflicting, and experimental study from a reliable animal model to explore the relationship is lacking. We reasoned that a mouse model that is sensitive to both lung injury and tumorigenesis would be appropriate to evaluate the exposure-risk relationship. Previously, we showed that, Gprc5a^−/− mice are susceptible to both lung tumorigenesis and endotoxin-induced acute lung injury. In this study, we investigated the biological consequences in Gprc5a^−/− mouse model following silica exposure. Intra-tracheal administration of fine silica particles in Gprc5a^−/− mice resulted in more severe lung injury and pulmonary inflammation than in wild-type mice. Moreover, an enhanced fibrogenic response, including EMT-like characteristics, was induced in the lungs of Gprc5a^−/− mice compared to those from wild-type ones. Importantly, increased hyperplasia or neoplasia coincided with silica-induced tissue injury and fibrogenic response in lungs from Gprc5a^−/− mice. Consistently, expression of MMP9, TGFβ1 and EGFR was significantly increased in lungs from silica-treated Gprc5a^−/− mice compared to those untreated or wild-type ones. These results suggest that, the process of tissue repair coincides with tissue damages; whereas persistent tissue damages leads to abnormal repair or neoplasia. Thus, silica-induced pulmonary inflammation and injury contribute to increased neoplasia development in lungs from Gprc5a^−/− mouse model.

CD151-α3β1 integrin complexes are prognostic markers of glioblastoma and cooperate with EGFR to drive tumor cell motility and invasion

Glioblastoma, one of the most aggressive forms of brain cancer, is featured by high tumor cell motility and invasiveness, which not only fuel tumor infiltration, but also enable escape from surgical or other clinical interventions. Thus, better understanding of how these malignant traits are controlled will be key to the discovery of novel biomarkers and therapies against this deadly disease. Tetraspanin CD151 and its associated α3β1 integrin have been implicated in facilitating tumor progression across multiple cancer types. How these adhesion molecules are involved in the progression of glioblastoma, however, remains largely unclear. Here, we examined an in-house tissue microarray-based cohort of 96 patient biopsies and TCGA dataset to evaluate the clinical significance of CD151 and α3β1 integrin. Functional and signaling analyses were also conducted to understand how these molecules promote the aggressiveness of glioblastoma at molecular and cellular levels. Results from our analyses showed that CD151 and α3 integrin were significantly elevated in glioblastomas at both protein and mRNA levels, and exhibited strong inverse correlation with patient survival (p < 0.006). These adhesion molecules also formed tight protein complexes and synergized with EGF/EGFR to accelerate tumor cell motility and invasion. Furthermore, disruption of such complexes enhanced the survival of tumor-bearing mice in a xenograft model, and impaired activation of FAK and small GTPases. Also, knockdown- or pharmacological agent-based attenuation of EGFR, FAK or Graf (ARHGAP26)/small GTPase-mediated pathways markedly mitigated the aggressiveness of glioblastoma cells. Collectively, our findings provide clinical, molecular and cellular evidence of CD151-α3β1 integrin complexes as promising prognostic biomarkers and therapeutic targets for glioblastoma.

Autocrine epiregulin activates EGFR pathway for lung metastasis via EMT in salivary adenoid cystic carcinoma

Salivary adenoid cystic carcinoma (SACC) is characterized by invasive local growth and a high incidence of lung metastasis. Patients with lung metastasis have a poor prognosis. Treatment of metastatic SACC has been unsuccessful, largely due to a lack of specific targets for the metastatic cells. In this study, we showed that epidermal growth factor receptors (EGFR) were constitutively activated in metastatic lung subtypes of SACC cells, and that this activation was induced by autocrine expression of epiregulin (EREG), a ligand of EGFR. Autocrine EREG expression was increased in metastatic SACC-LM cells compared to that in non-metastatic parental SACC cells. Importantly, EREG-neutralizing antibody, but not normal IgG, blocked the autocrine EREG-induced EGFR phosphorylation and the migration of SACC cells, suggesting that EREG-induced EGFR activation is essential for induction of cell migration and invasion by SACC cells. Moreover, EREG-activated EGFR stabilized Snail and Slug, which promoted EMT and metastatic features in SACC cells. Of note, targeting EGFR with inhibitors significantly suppressed both the motility of SACC cells in vitro and lung metastasis in vivo. Finally, elevated EREG expression showed a strong correlation with poor prognosis in head and neck cancer. Thus, targeting the EREG-EGFR-Snail/Slug axis represents a novel strategy for the treatment of metastatic SACC even no genetic EGFR mutation.

Twist-mediated Epithelial-mesenchymal Transition Promotes Breast Tumor Cell Invasion via Inhibition of Hippo Pathway

Twist is a key transcription factor for Epithelial-mesenchymal transition (EMT), which is a cellular de-differentiation program that promotes invasion and metastasis, confers tumor cells with cancer stem cell (CSC)-like characteristics, and increases therapeutic resistance. However, the mechanisms that facilitate the functions of Twist remain unclear. Here we report that Twist overexpression increased expression of PAR1, an upstream regulator of the Hippo pathway; PAR1 promotes invasion, migration, and CSC-like properties in breast cancer by activating the transcriptional co-activator TAZ. Our study indicates that Hippo pathway inhibition is required for the increased migratory and invasiveness ability of breast cancer cells in Twist-mediated EMT.

Inflammation fuels tumor progress and metastasis

Inflammation is a beneficial response that can remove pathogens, repair injured tissue and restore homeostasis to damaged tissues and organs. However, increasing evidence indicate that chronic inflammation plays a pivotal role in tumor development, as well as progression, metastasis, and resistance to chemotherapy. We will review the current knowledge regarding the contribution of inflammation to epithelial mesenchymal transition. We will also provide some perspectives on the relationship between ER-stress signals and metabolism, and the role of these processes in the development of inflammation.

G9a is essential for EMT-mediated metastasis and maintenance of cancer stem cell-like characters in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a particularly aggressive cancer with poor prognosis, largely due to lymph node metastasis and local recurrence. Emerging evidence suggests that epithelial-to-mesenchymal transition (EMT) is important for cancer metastasis, and correlated with increased cancer stem cells (CSCs) characteristics. However, the mechanisms underlying metastasis to lymph nodes in HNSCC is poorly defined. In this study, we show that E-cadherin repression correlates with cancer metastasis and poor prognosis in HNSCC. We found that G9a, a histone methyltransferase, interacts with Snail and mediates Snail-induced transcriptional repression of E-cadherin and EMT, through methylation of histone H3 lysine-9 (H3K9). Moreover, G9a is required for both lymph node-related metastasis and TGF-β-induced EMT in HNSCC cells since knockdown of G9a reversed EMT, inhibited cell migration and tumorsphere formation, and suppressed the expression of CSC markers. Our study demonstrates that the G9a protein is essential for the induction of EMT and CSC-like properties in HNSCC. Thus, targeting the G9a-Snail axis may represent a novel strategy for treatment of metastatic HNSCC.

Autophagy regulation in the development and treatment of breast cancer

Autophagy is a major catabolic process in which intracellular membrane structures, protein complexes, and lysosomes are formed as lysoautophagosome to degrade and renew cytoplasmic components. Autophagy is physiologically a strategy and mechanism for cellular homeostasis as well as adaptation to stress, and thus alterations in the autophagy machinery may lead to diverse pathological conditions. The role of autophagy in cancer is complex, and the current literature reflects this as a 'double-edged sword'. Autophagy shows promise as a novel therapeutic target in various types of breast cancer, inhibiting or increasing treatment efficacy in a context- and cell-type-dependent manner. This review aims to summarize the recent advances in the understanding of the mechanisms by which key modulators of autophagy participate in cancer metastasis, highlight different autophagy-deficient murine models for breast cancer study, and provide further impetus for the modulation of autophagy in anticancer therapy.

Metabolic rewiring in cancer-associated fibroblasts provides a niche for oncogenesis and metastatic dissemination

Cancer-associated fibroblasts (CAFs) are major participants in the crosstalk between tumor cells and their microenvironment. CAFs provide not only multiple soluble factors but also metabolic fuels to promote tumor growth, invasion, and metastasis. We discuss recent developments delineating the effects of metabolic symbiosis between CAFs and tumor cells on tumor growth.

Twist-BRD4 complex: potential drug target for basal-like breast cancer

As an important basic helix-loop-helix (bHLH) transcription factor, Twist associates with several physiological processes such as mesodermal development, and pathological processes such as Saethre-Chotzen syndrome. During cancer progression, Twist induces epithelial-mesenchymal transition (EMT), potentiating cancer cell invasion and metastasis. Although many studies have revealed its multiple biological roles, it remained unclear how Twist transcriptionally activates targeted genes. Recently we discovered tip60-mediated Twist di-acetylation in the ''histone H4-mimic'' GK-X-GK motif. The di-acetylated Twist recruits BRD4 and related transcriptional components to super-enhancer of its targeted genes during progression of basal-like breast cancer (BLBC). Here, we review this new advance of regulation and functional mechanism of Twist.

CD151-α3β1 integrin complexes suppress ovarian tumor growth by repressing slug-mediated EMT and canonical Wnt signaling

Human ovarian cancer is diagnosed in the late, metastatic stages but the underlying mechanisms remain poorly understood. We report a surprising functional link between CD151-α3β1 integrin complexes and the malignancy of serous-type ovarian cancer. Analyses of clinical specimens indicate that CD151 expression is significantly reduced or diminished in 90% of metastatic lesions, while it remains detectable in 58% of primary tumors. These observations suggest a putative tumor-suppressing role of CD151 in ovarian cancer. Indeed, our analyses show that knocking down CD151 or α3 integrin enhances tumor cell proliferation, growth and ascites production in nude mice. These changes are accompanied by impaired cell-cell contacts and aberrant expression of E-cadherin, Mucin 5AC and fibronectin, largely reminiscent of an epithelial to mesenchymal transition (EMT)-like change. Importantly, Slug, a master regulator of EMT, is markedly elevated. Knocking down Slug partially restores CD151-α3β1 integrin complex-dependent suppression of cell proliferation. Moreover, disruption of these adhesion protein complexes is accompanied by a concomitant activation of canonical Wnt signaling, including elevated levels of β-catenin and Axin-2 as well as resistance to the inhibition in β-catenin-dependent transcriptional complexes. Together, our study demonstrates that CD151-α3β1 integrin complexes regulate ovarian tumor growth by repressing Slug-mediated EMT and Wnt signaling.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead

Low-dose exposures to common environmental chemicals that are deemed safe individually may be combining to instigate carcinogenesis, thereby contributing to the incidence of cancer. This risk may be overlooked by current regulatory practices and needs to be vigorously investigated.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety ‘Mode of Action’ framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

CD151 represses mammary gland development by maintaining the niches of progenitor cells

Tetraspanin CD151 interacts with laminin-binding integrins (i.e., α3β1, α6β1 and α6β4) and other cell surface molecules to control diverse cellular and physiological processes, ranging from cell adhesion, migration and survival to tissue architecture and homeostasis. Here, we report a novel role of CD151 in maintaining the branching morphogenesis and activity of progenitor cells during the pubertal development of mammary glands. In contrast to the disruption of laminin-binding integrins, CD151 removal in mice enhanced the tertiary branching in mammary glands by 2.4-fold and the number of terminal end buds (TEBs) by 30%, while having minimal influence on either primary or secondary ductal branching. Consistent with these morphological changes are the skewed distribution of basal/myoepithelial cells and a 3.2-fold increase in proliferating Ki67-positive cells. These novel observations suggest that CD151 impacts the branching morphogenesis of mammary glands by upregulating the activities of bipotent progenitor cells. Indeed, our subsequent analyses indicate that upon CD151 removal the proportion of CD24(Hi)CD49f(Low) progenitor cells in the mammary gland increased by 34%, and their proliferating and differentiating activities were significantly upregulated. Importantly, fibronectin, a pro-branching extracellular matrix (ECM) protein deposited underlying mammary epithelial or progenitor cells, increased by >7.2-fold. Moreover, there was a concomitant increase in the expression and nuclear distribution of Slug, a transcription factor implicated in the maintenance of mammary progenitor cell activities. Taken together, our studies demonstrate that integrin-associated CD151 represses mammary branching morphogenesis by controlling progenitor cell activities, ECM integrity and transcription program.

Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

GPRC5A is a G-protein-coupled receptor expressed in lung tissue but repressed in most human lung cancers. Studies in Gprc5a(-/-) mice have established its role as a tumor-suppressor function in this setting, but the basis for its role has been obscure. Here, we report that GPRC5A functions as a negative modulator of EGFR signaling. Mouse tracheal epithelial cells (MTEC) from Gprc5a(-/-) mice exhibited a relative increase in EGFR and downstream STAT3 signaling, whereas GPRC5A expression inhibited EGFR and STAT3 signaling. GPRC5A physically interacted with EGFR through its transmembrane domain, which was required for its EGFR inhibitory activity. Gprc5a(-/-) MTEC were much more susceptible to EGFR inhibitors than wild-type MTEC, suggesting their dependence on EGFR signaling for proliferation and survival. Dysregulated EGFR and STAT3 were identified in the normal epithelia of small and terminal bronchioles as well as tumors of Gprc5a(-/-) mouse lungs. Moreover, in these lungs EGFR inhibitor treatment inhibited EGFR and STAT3 activation along with cell proliferation. Finally, overexpression of ectopic GPRC5A in human non-small cell lung carcinoma cells inhibited both EGF-induced and constitutively activated EGFR signaling. Taken together, our results show how GPRC5A deficiency leads to dysregulated EGFR and STAT3 signaling and lung tumorigenesis. Cancer Res; 75(9); 1801-14. ©2015 AACR.

Chaperone Hsp47 Drives Malignant Growth and Invasion by Modulating an ECM Gene Network

The extracellular matrix (ECM) is a determining factor in the tumor microenvironment that restrains or promotes malignant growth. In this report, we show how the molecular chaperone protein Hsp47 functions as a nodal hub in regulating an ECM gene transcription network. A transcription network analysis showed that Hsp47 expression was activated during breast cancer development and progression. Hsp47 silencing reprogrammed human breast cancer cells to form growth-arrested and/or noninvasive structures in 3D cultures, and to limit tumor growth in xenograft assays by reducing deposition of collagen and fibronectin. Coexpression network analysis also showed that levels of microRNA(miR)-29b and -29c were inversely correlated with expression of Hsp47 and ECM network genes in human breast cancer tissues. We found that miR-29 repressed expression of Hsp47 along with multiple ECM network genes. Ectopic expression of miR-29b suppressed malignant phenotypes of breast cancer cells in 3D culture. Clinically, increased expression of Hsp47 and reduced levels of miR-29b and -29c were associated with poor survival outcomes in breast cancer patients. Our results show that Hsp47 is regulated by miR-29 during breast cancer development and progression, and that increased Hsp47 expression promotes cancer progression in part by enhancing deposition of ECM proteins.

Metabolic reprogramming of cancer-associated fibroblasts by IDH3α downregulation

Cancer-associated fibroblasts (CAFs) provide critical metabolites for tumor growth and undergo metabolic reprogramming to support glycolysis. However, the molecular mechanisms responsible for this change remain unclear. Here, we report that TGF-β1- or PDGF-induced CAFs switch from oxidative phosphorylation to aerobic glycolysis. We identify downregulation of isocitrate dehydrogenase 3α (IDH3α) as a marker for this switch. Furthermore, miR-424 downregulates IDH3α during CAF formation. Downregulation of IDH3α decreases the effective level of α-ketoglutarate (α-KG) by reducing the ratio of α-KG to fumarate and succinate, resulting in PHD2 inhibition and HIF-1α protein stabilization. The accumulation of HIF-1α, in turn, promotes glycolysis by increasing the uptake of glucose, upregulating expression of glycolytic enzymes under normoxic conditions, and inhibiting oxidative phosphorylation by upregulating NDUFA4L2. CAFs from tumor samples exhibit low levels of IDH3α, and overexpression of IDH3α prevents transformation of fibroblasts into CAFs. Our studies reveal IDH3α to be a critical metabolic switch in CAFs.