c-Ski activates cancer-associated fibroblasts to regulate breast cancer cell invasion

Upregulation of FGF9 and NOVA1 in cancer-associated fibroblasts promotes cell proliferation, invasion and migration of triple negative breast cancer

Cancer-associated fibroblasts (CAFs) play a pivotal role in cancer progression. This study aimed to explore the roles of CAFs-derived Fibroblast growth factor 9 (FGF9) and Neuro-oncological ventral antigen 1 (NOVA1) in triple negative breast cancer (TNBC) progression. MDA-MB-231 and BT-549 cells were cocultured with CAF conditioned-medium (CAF-CM) or normal fibroblasts conditioned-medium (NF-CM). MTT, EdU, colony formation, wound healing, transwell migration, and invasion assays were employed to determine cell proliferation, migration and invasion, respectively. Western blot and RT-qPCR were carried out to examine the protein and mRNA expression of FGF9 and NOVA1. Xenograft tumor experiments were conducted to evaluate the effects of CAFs, FGF9, and NOVA1 on tumor growth in vivo. Our results showed that CAFs significantly promoted the proliferation, invasion, and migration of TNBC cells. FGF9 and NOVA1 were significantly upregulated in TNBC CAFs, tissues and cells. CAF-CM also could increase the expression of FGF9 and NOVA1 in TNBC cells. Knockdown of FGF9 or NOVA1 could hamper cell proliferation, invasion, migration, and EMT of TNBC cells. Moreover, CAFs with FGF9/NOVA1 knockdown also could inhibit TNBC progression. Besides, CAFs significantly accelerated tumor growth in vivo, which was blocked by FGF9/NOVA1 knockdown in nude mice. In conclusion, our results indicated the tumor-promoting role of CAFs in TNBC progression. FGF9 and NOVA1 upregulation in CAFs induced cell proliferation, migration and invasion in vitro, and facilitated tumor growth in vivo in TNBC development.

The role of transcription factors in the crosstalk between cancer-associated fibroblasts and tumor cells

BACKGROUND

Transcription factors (TFs) fulfill a critical role in the formation and maintenance of different cell types during the developmental process as well as disease. It is believed that cancer-associated fibroblasts (CAFs) are activation status of tissue-resident fibroblasts or derived from form other cell types via transdifferentiation or dedifferentiation. Despite a subgroup of CAFs exhibit anti-cancer effects, most of them are reported to exert effects on tumor progression, further indicating their heterogeneous origin.

AIM OF REVIEW

This review aimed to summarize and review the roles of TFs in the reciprocal crosstalk between CAFs and tumor cells, discuss the emerging mechanisms, and their roles in cell-fate decision, cellular reprogramming and advancing our understanding of the gene regulatory networks over the period of cancer initiation and progression.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This manuscript delves into the key contributory factors of TFs that are involved in activating CAFs and maintaining their unique states. Additionally, it explores how TFs play a pivotal and multifaceted role in the reciprocal crosstalk between CAFs and tumor cells. This includes their involvement in processes such as epithelial-mesenchymal transition (EMT), proliferation, invasion, and metastasis, as well as metabolic reprogramming. TFs also have a role in constructing an immunosuppressive microenvironment, inducing resistance to radiation and chemotherapy, facilitating angiogenesis, and even 'educating' CAFs to support the malignancies of tumor cells. Furthermore, this manuscript delves into the current status of TF-targeted therapy and considers the future directions of TFs in conjunction with anti-CAFs therapies to address the challenges in clinical cancer treatment.

The role of cancer-associated fibroblasts in breast cancer metastasis

Breast cancer deaths are primarily caused by metastasis. There are several treatment options that can be used to treat breast cancer. There are, however, a limited number of treatments that can either prevent or inhibit the spread of breast tumor metastases. Thus, novel therapeutic strategies are needed. Studies have increasingly focused on the importance of the tumor microenvironment (TME) in metastasis of breast cancer. As the most abundant cells in the TME, cancer-associated fibroblasts (CAFs) play important roles in cancer pathogenesis. They can remodel the structure of the extracellular matrix (ECM) and engage in crosstalk with cancer cells or other stroma cells by secreting growth factors, cytokines, and chemokines, as well as components of the ECM, which assist the tumor cells to invade through the TME and cause distant metastasis. Clinically, CAFs not only foster the initiation, growth, angiogenesis, invasion, and metastasis of breast cancer but also serve as biomarkers for diagnosis, therapy, and prediction of prognosis. In this review, we summarize the biological characteristics and subtypes of CAFs and their functions in breast cancer metastasis, focusing on their important roles in the diagnosis, prognosis, and treatment of breast cancer. Recent studies suggest that CAFs are vital partners of breast cancer cells that assist metastasis and may represent ideal targets for prevention and treatment of breast cancer metastasis.

TCF12 regulates exosome release from epirubicin-treated CAFs to promote ER+ breast cancer cell chemoresistance

Cancer-associated fibroblasts (CAFs) are the predominant stromal cells in the microenvironment and play important roles in tumor progression, including chemoresistance. However, the response of CAFs to chemotherapeutics and their effects on chemotherapeutic outcomes are largely unknown. In this study, we showed that epirubicin (EPI) treatment triggered ROS which initiated autophagy in CAFs, TCF12 inhibited autophagy flux and further promoted exosome secretion. Inhibition of EPI-induced reactive oxygen species (ROS) production with N-acetyl-L-cysteine (NAC) or suppression of autophagic initiation with short interfering RNA (siRNA) against ATG5 blunted exosome release from CAFs. Furthermore, exosome secreted from EPI-treated CAFs not only prevented ROS accumulation in CAFs but also upregulated the CXCR4 and c-Myc protein levels in recipient ER+ breast cancer cells, thus promoting EPI resistance of tumor cells. Together, the current study provides novel insights into the role of stressed CAFs in promoting tumor chemoresistance and reveal a new function of TCF12 in regulating autophagy impairment and exosome release.

Upregulation of proto-oncogene ski by thyroid hormone in the intestine and tail during Xenopus metamorphosis

Thyroid hormone (T3) is important for adult organ function and vertebrate development, particularly during the postembryonic period when many organs develop/mature into their adult forms. Amphibian metamorphosis is totally dependent on T3 and can be easily manipulated, thus offering a unique opportunity for studying how T3 controls postembryonic development in vertebrates. Numerous early studies have demonstrated that T3 affects frog metamorphosis through T3 receptor (TR)-mediated regulation of T3 response genes, where TR forms a heterodimer with RXR (9-cis retinoic acid receptor) and binds to T3 response elements (TREs) in T3 response genes to regulate their expression. We have previously identified many candidate direct T3 response genes in Xenopus tropicalis tadpole intestine. Among them is the proto-oncogene Ski, which encodes a nuclear protein with complex function in regulating cell fate. We show here that Ski is upregulated in the intestine and tail of premetamorphic tadpoles upon T3 treatment and its expression peaks at stage 62, the climax of metamorphosis. We have further discovered a putative TRE in the first exon that can bind to TR/RXR in vitro and mediate T3 regulation of the promoter in vivo. These data demonstrate that Ski is activated by T3 through TR binding to a TRE in the first exon during Xenopus tropicalis metamorphosis, implicating a role of Ski in regulating cell fate during metamorphosis.

Origin, activation and heterogeneity of fibroblasts associated with pancreas and breast cancers

Pancreas and breast cancers both contain abundant stromal components within the tumor tissues. A prominent cell type within the stroma is cancer-associated fibroblasts (CAFs). CAFs play critical and complex roles establishing the tumor microenvironment to either promote or prevent tumor progression. Recently, complex genetic models and single cell-based techniques have provided emerging insights on the precise functions and cellular heterogeneity of CAFs. The transformation of normal fibroblasts into CAFs is a key event during tumor initiation and progression. Such coordination between tumor cells and fibroblasts plays an important role in cancer development. Reprograming fibroblasts is currently being explored for therapeutic benefits. In this review, we will discuss recent literature shedding light on the tissues of origin, activation mechanisms, and heterogeneity of CAFs comparing pancreas and breast cancers.

GPR30-mediated HMGB1 upregulation in CAFs induces autophagy and tamoxifen resistance in ERα-positive breast cancer cells

Tamoxifen (TAM) resistance constitutes a challenge in managing estrogen receptor (ER)α+ breast cancer patients. G-protein-coupled estrogen receptor (GPR30/GPER), which reportedly initiates TAM resistance in ERα+/ GPR30+ breast cancers, is detected in the breast cancer microenvironment, especially cancer associated fibroblasts (CAFs). Herein, considering that GPR30 mediates transcriptional regulation in different cell backgrounds, a microarray strategy was applied in immortalized CAFs derived from primary breast cancer samples, resulting in the identification of 165 GPR30 target genes, among which HMGB1 was confirmed to be upregulated by 17-β estradiol(E2)- and TAM-triggered GPR30 activation in CAFs. Activated GPR30 increased extracellular HMGB1 secretion by CAFs, which was reduced by blocking PI3K/AKT signaling using G15 or LY294002. GPR30-induced HMGB1 upregulation triggered MEK/ERK signaling, leading to increased autophagic behavior to protect cancer cells from TAM-induced apoptosis, mimicking the recombinant HMGB1-mediated increase in cancer cell resistance potential to TAM. MEK/ERK signaling blockage by U0126 decreased the autophagic behavior and resistance ability of cancer cells to TAM. CAF-expressed GPR30 induced TAM resistance via HMGB1 in vivo. Overall, TAM upregulated HMGB1 expression and secretion in CAFs via GPR30/PI3K/AKT signaling, and the secreted HMGB1 induced autophagy to enhance TAM resistance in MCF-7 cells in an ERK-dependent manner. Thus, targeting GPR30 and downstream cascades may be an effective strategy to attenuate the resistance of ERα-positive breast tumors to endocrine therapy.

Long non-coding RNA Lnc-408 promotes invasion and metastasis of breast cancer cell by regulating LIMK1

Invasion and metastasis are the leading causes of death in patients with breast cancer (BC), and epithelial-mesenchymal transformation (EMT) plays an essential role in this process. Here, we found that Lnc-408, a novel long noncoding RNA (lncRNA), is significantly upregulated in BC cells undergoing EMT and in BC tumor with lymphatic metastases compared with those without lymphatic metastases. Lnc-408 can enhance BC invasion and metastasis by regulating the expression of LIMK1. Mechanistically, Lnc-408 serves as a sponge for miR-654-5p to relieve the suppression of miR-654-5p on its target LIMK1. Knockdown or knockout of Lnc-408 in invasive BC cells clearly decreased LIMK1 levels, and ectopic Lnc-408 in MCF-7 cells increased LIMK1 expression to promote cell invasion. Lnc-408-mediated enhancement of LIMK1 plays a key role in cytoskeletal stability and promotes invadopodium formation in BC cells via p-cofilin/F-actin. In addition, the increased LIMK1 also facilitates the expression of MMP2, ITGB1, and COL1A1 by phosphorylating CREB. In conclusion, our findings reveal that Lnc-408 promotes BC invasion and metastasis via the Lnc-408/miR-654-5p/LIMK1 axis, highlighting a novel promising target for the diagnosis and treatment of BC.

A novel Lnc408 maintains breast cancer stem cell stemness by recruiting SP3 to suppress CBY1 transcription and increasing nuclear β-catenin levels

Tumor initiation, development, and relapse may be closely associated with cancer stem cells (CSCs). The complicated mechanisms underlying the maintenance of CSCs are keeping in illustration. Long noncoding RNAs (lncRNAs), due to their multifunction in various biological processes, have been indicated to play a crucial role in CSC renewal and stemness maintenance. Using lncRNA array, we identified a novel lncRNA (named lnc408) in epithelial-mesenchymal transition-related breast CSCs (BCSCs). The lnc408 is high expressed in BCSCs in vitro and in vivo. The enhanced lnc408 is critical to BCSC characteristics and tumorigenesis. Lnc408 can recruit transcript factor SP3 to CBY1 promoter to serve as an inhibitor in CBY1 transcription in BCSCs. The high expressed CBY1 in non-BCSC interacts with 14-3-3 and β-catenin to form a ternary complex, which leads a translocation of the ternary complex into cytoplasm from nucleus and degradation of β-catenin in phosphorylation-dependent pattern. The lnc408-mediated decrease of CBY1 in BCSCs impairs the formation of 14-3-3/β-catenin/CBY1 complex, and keeps β-catenin in nucleus to promote CSC-associated CD44, SOX2, Nanog, Klf4, and c-Myc expressions and contributes to mammosphere formation; however, restoration of CBY1 expression in tumor cells reduces BCSC and its enrichment, thus lnc408 plays an essential role in maintenance of BCSC stemness. In shortly, these findings highlight that the novel lnc408 functions as an oncogenic factor by recruiting SP3 to inhibit CBY1 expression and β-catenin accumulation in nucleus to maintain stemness properties of BCSCs. Lnc408-CBY1-β-catenin signaling axis might serve as a new diagnostic and therapeutic target for breast cancer.

FOSL2 promotes VEGF-independent angiogenesis by transcriptionnally activating Wnt5a in breast cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs), a predominant component of the tumor microenvironment, contribute to aggressive angiogenesis progression. In clinical practice, traditional anti-angiogenic therapy, mainly anti-VEGF, provides extremely limited beneficial effects to breast cancer. Here, we reveal that FOS-like 2 (FOSL2), a transcription factor in breast CAFs, plays a critical role in VEGF-independent angiogenesis in stromal fibroblasts.

Methods: FOSL2 and Wnt5a expression was assessed by qRT-PCR, western blotting and immunohistochemistry in primary and immortalized CAFs and clinical samples. FOSL2- or Wnt5a-silenced CAFs and FOSL2-overexpressing NFs were established to explore their proangiogenic effects. Invasion, tubule formation, three-dimensional sprouting assays, and orthotopic xenografts were conducted as angiogenesis experiments. FZD5/NF-κB/ERK signaling activation was evaluated by western blotting after blocking VEGF/VEGFR with an anti-VEGF antibody and axitinib. Dual luciferase reporter assays and chromatin immunoprecipitation were performed to test the role of FOSL2 in regulating Wnt5a expression, and Wnt5a in the serum of the patients was measured to assess its clinical diagnostic value for breast cancer patients.

Results: Enhanced FOSL2 in breast CAFs was significantly associated with angiogenesis and clinical progression in patients. The supernatant from CAFs highly expressing FOSL2 strongly promoted tube formation and sprouting of human umbilical vein endothelial cells (HUVECs) in a VEGF-independent manner and angiogenesis as well as tumor growth in vivo. Mechanistically, the enhanced FOSL2 in CAFs was regulated by estrogen/cAMP/PKA signaling. Wnt5a, a direct target of FOSL2, specifically activated FZD5/NF-κB/ERK signaling in HUVECs to promote VEGF-independent angiogenesis. In addition, a high level of Wnt5a was commonly detected in the serum of breast cancer patients and closely correlated with microvessel density in breast tumor tissues, suggesting a promising clinical value of Wnt5a for breast cancer diagnostics.

Conclusion: FOSL2/Wnt5a signaling plays an essential role in breast cancer angiogenesis in a VEGF-independent manner, and targeting the FOSL2/Wnt5a signaling axis in CAFs may offer a potential option for antiangiogenesis therapy.

Effects of differential distributed-JUP on the malignancy of gastric cancer

JUP, a homologue of β-catenin, is a cell-cell junction protein involved in adhesion junction and desmosome composition. JUP may have a controversial role in different malignancies dependence of its competence with or collaboration with β-catenin as a transcription factor. In this study, we reveal that the function of JUP is related to its cellular location in GC development process from epithelium-like, low malignant GC to advanced EMT-phenotypic GC. Gradual loss of membrane and/or cytoplasm JUP is closely correlated with GC malignancy and poor prognostics. Knockdown of JUP in epithelium-like GC cells causes EMT and promotes GC cell migration and invasion. Ectopic expression of wild JUP in malignant GC cells leads to an attenuated malignant phenotype such as reduced cell invasive potential. In mechanism, loss of membrane and/or cytoplasm JUP abolishes the restrain of JUP to EGFR at cell membrane and results in increased p-AKT levels and AKT/GSK3β/β-catenin signaling activity. In addition, nuclear JUP interacts with nuclear β-catenin and TCF4 and plays a synergistic role with β-catenin in promoting TCF4 transcription and its downstream target MMP7 expression to fuel GC cell invasion.

Ski: Double roles in cancers

The Ski (Sloan-Kettering Institute) is an evolutionarily conserved protein that plays a dual role as an oncoprotein and tumor suppressor gene in the development of human cancer. The Ski oncogene was first identified as a transforming protein of the avian Sloan-Kettering retrovirus in 1986. Since its discovery, Ski has been identified as a carcinogenic regulator in a variety of malignant tumors. Later, it was reported that Ski regulates the occurrence and development of some cancers by acting as an oncogene. Ski mediates the proliferation, differentiation, metastasis, and invasion of numerous cancer cells through various mechanisms. Several studies have shown that Ski expression is correlated with the clinical characteristics of cancer patients and is a promising biomarker and therapeutic target for cancer. In this review, we summarize the mechanisms and potential clinical implications of Ski in dimorphism, cancer occurrence, and progression in various types of cancer.

Oxidized ATM promotes breast cancer stem cell enrichment through energy metabolism reprogram-mediated acetyl-CoA accumulation

Cancer stem cell (CSC) is a challenge in the therapy of triple-negative breast cancer (TNBC). Intratumoral hypoxia is a common feature of solid tumor. Hypoxia may contribute to the maintenance of CSC, resulting in a poor efficacy of traditional treatment and recurrence of TNBC cases. However, the underlying molecular mechanism involved in hypoxia-induced CSC stemness maintenance remains unclear. Here, we report that hypoxia stimulated DNA double-strand breaks independent of ATM kinase activation (called oxidized ATM in this paper) play a crucial role in TNBC mammosphere formation and stemness maintenance by governing a specific energy metabolism reprogramming (EMR). Oxidized ATM up-regulates GLUT1, PKM2, and PDHa expressions to enhance the uptake of glucose and production of pyruvate rather than lactate products, which facilitates glycolytic flux to mitochondrial pyruvate and citrate, thus resulting in accumulation of cytoplasmic acetyl-CoA instead of the tricarboxylic acid (TCA) cycle by regulating ATP-citrate lyase (ACLY) activity. Our findings unravel a novel model of TNBC-CSC glucose metabolism and its functional role in maintenance of hypoxic TNBC-CSC stemness. This work may help us to develop new therapeutic strategies for TNBC treatment.

Knockdown of Ski decreases osteosarcoma cell proliferation and migration by suppressing the PI3K/Akt signaling pathway

Ski, an evolutionary conserved protein, is involved in the development of a number of tumors, such as Barrett's esophagus, leukemia, colorectal cancer, gastric cancer, pancreatic cancer, hemangiomas and melanoma. However, studies on the functions of Ski in osteosarcoma (OS) are limited. In this study, firstly the differential expression of Ski in OS tissues and osteochondroma tissues was detected, and the expression of Ski in both human OS cell lines (MG63 and U2OS) and normal osteoblasts (hFoB1.19) was then detected. The results demonstrated that Ski expression was significantly upregulated in both human OS tissues and cell lines. The results led us to hypothesize that Ski may play an essential role in the pathological process of OS. Thus, Ski specific small interfere RNA (Ski-siRNA) was used. The results revealed that OS cell proliferation was markedly inhibited following the knockdown of Ski, which was identified by CCK8 assay, EdU staining and cell cycle analysis. In addition, OS cell migration was significantly suppressed following Ski knockdown, which was identified by wound healing assay. Moreover, the protein levels of p-PI3K and p-Akt in OS cells declined prominently following Ski knockdown. On the whole, the findings of this study revealed that Ski expression was significantly upregulated in OS tissue and OS cells. The knockdown of Ski decreased OS cell proliferation and migration, which was mediated by blocking the PI3K/Akt signaling pathway. Thus, Ski may act as a tumor promoter gene in tumorigenesis, and Ski may prove to be a potential therapeutic target for the treatment of OS.

CXCL1 stimulates migration and invasion in ER‑negative breast cancer cells via activation of the ERK/MMP2/9 signaling axis

Chemokine (C‑X‑C motif) ligand 1 (CXCL1), a member of the CXC chemokine family, has been reported to be a critical factor in inflammatory diseases and tumor progression; however, its functions and molecular mechanisms in estrogen receptor α (ER)‑negative breast cancer (BC) remain largely unknown. The present study demonstrated that CXCL1 was upregulated in ER‑negative BC tissues and cell lines compared with ER‑positive tissues and cell lines. Treatment with recombinant human CXCL1 protein promoted ER‑negative BC cell migration and invasion in a dose‑dependent manner, and stimulated the activation of phosphorylated (p)‑ extracellular signal‑regulated kinase (ERK)1/2, but not p‑STAT3 or p‑AKT. Conversely, knockdown of CXCL1 in BC cells attenuated these effects. Additionally, CXCL1 increased the expression of matrix metalloproteinase (MMP)2/9 via the ERK1/2 pathway. Inhibition of MEK1/2 by its antagonist U0126 reversed the effects of CXCL1 on MMP2/9 expression. Furthermore, immunohistochemical analysis revealed a strong positive association between CXCL1 and p‑ERK1/2 expression levels in BC tissues. In conclusion, the present study demonstrated that CXCL1 is highly expressed in ER‑negative BC, and stimulates BC cell migration and invasion via the ERK/MMP2/9 pathway. Therefore, CXCL1 may serve as a potential therapeutic target in ER‑negative BC.

Autocrine TGF-β1/miR-200s/miR-221/DNMT3B regulatory loop maintains CAF status to fuel breast cancer cell proliferation

Cancer-associated fibroblasts (CAFs) remain active even in the absence of cancer cells. However, the molecular mechanism underlying the sustained active status of CAFs is largely unrevealed. We found that in CAFs, DNMT3B was not only a target of miR-200b, miR-200c and miR-221, but was able to induce DNA methylation of miR-200s promoters. DNMT3B eventually reached a stably high level by the counteracting effect of decreasing miR-200b/c and increasing miR-221 in normal fibroblasts (NFs) with long-term exogenous TGF-β1 treatment, and DNMT3B further led to a low level of miR-200s which established CAF activation. Meanwhile, miR-200s/miR-221/DNMT3B signaling sustained autocrine TGF-β1 maintaining active CAF status. Destruction of the autocrine TGF-β1/miR-200s/miR-221/DNMT3B signaling led to demethylation of miR-200s promoters and further restored the NF phenotypes. Moreover, we confirmed that TCF12, the target of miR-141, stimulated c-Myc/Cyclin D1 axis in breast cancer cells to promote cancer growth by enhancing CXCL12 of CAFs. The current study reveals that the TGF-β1/miR-200s/miR-221/DNMT3B regulatory loop is responsible for the maintenance of CAFs status and is also necessary for CAF function in promoting malignance of breast cancer, which provides a potential target for CAF-driven therapeutic strategy.

Oxidized ATM-mediated glycolysis enhancement in breast cancer-associated fibroblasts contributes to tumor invasion through lactate as metabolic coupling

BACKGROUND

Cancer-associated fibroblasts (CAFs) are the predominant residents in the breast tumor microenvironment. In our work, we found activation of DNA damage-independent ATM (oxidized ATM), enhanced glycolysis and aberrant metabolism-associated gene expressions in breast CAFs. Nevertheless, whether and how oxidized ATM regulates the glycolytic activity of CAFs keep in unveil. Recently, a reverse Warburg effect was observed in tumor tissues, in which host cells (such as CAFs, PSCs) in the tumor microenvironment have been found to "fuel" the cancer cells via metabolites transfer. However, the molecular mechanisms of the metabolites from stromal cells playing a role to the progression of cancer cells remain to be determined.

METHODS

Oxidized ATM activation in stromal CAFs was assessed by western blotting and immunofluorescence. The increased glycolytic ability of CAFs was validated by measurements of OCR and ECAR and detections of glucose consumption and lactate production. Kinase assay and western blotting were performed to confirm the phosphorylation of GLUT1. The membrane location of phosphorylated GLUT1 was determined by biotin pull-down assay and immunofluorescence staining. The regulation of PKM2 through oxidized ATM was evaluated by western blots. In addition, the impact of lactate derived from hypoxic CAFs on cancer cell invasion was investigated both in vitro (transwell assays, western blots) and in vivo (orthotopic xenografts).

FINDINGS

Hypoxia-induced oxidized ATM promotes glycolytic activity of CAFs by phosphorylating GLUT1 at S490 and increasing PKM2 expression. Moreover, lactate derived from hypoxic CAFs, acting as a metabolic coupling between CAFs and breast cancer cells, promotes breast cancer cell invasion by activating the TGFβ1/p38 MAPK/MMP2/9 signaling axis and fueling the mitochondrial activity in cancer cells.

INTERPRETATION

Our work shows that oxidized ATM-mediated glycolysis enhancement in hypoxic stromal fibroblasts plays an essential role in cancer cell invasion and metastasis and may implicate oxidized ATM as a target for breast tumor treatment. FUND: This research was supported by National Natural Science Foundation of China.

HepaCAM inhibits cell proliferation and invasion in prostate cancer by suppressing nuclear translocation of the androgen receptor via its cytoplasmic domain

Hepatocyte cell adhesion molecule (HepaCAM) is a tumour suppressor. However, the mechanism of HepaCAM function in prostate cancer (PCa) remains unknown. In the present study, HepaCAM, androgen receptor (AR) and Ran were analysed in 46 PCa tissue samples using immunohistochemistry. Subsequently, the influence of HepaCAM and its cytoplasmic domain on cell proliferation, migration, and invasion, and associated proteins was examined using MTT, wound healing, Transwell and western blotting assays, respectively. Furthermore, nuclear translocation of AR and Ran was analysed using immunofluorescence and Western blot assays. The results demonstrated that HepaCAM expression was reduced in PCa, and there was an association between downregulation of HepaCAM and changes in the distribution of AR and Ran. Furthermore, HepaCAM, specifically the cytoplasmic domain, was involved in cell proliferation, migration and invasion. Nuclear translocation of AR was dependent on HepaCAM and its cytoplasmic domain. Additionally, HepaCAM suppression of the nuclear translocation of AR occurred via Ran. The results suggest that HepaCAM and its cytoplasmic domain suppress the nuclear translocation of AR via Ran in PCa. The cytoplasmic domain of HepaCAM may serve as a novel target for therapy in PCa.

Cancer-associated fibroblast (CAF)-derived IL32 promotes breast cancer cell invasion and metastasis via integrin β3-p38 MAPK signalling

Metastasis is the leading cause of breast cancer-related deaths. Cancer-associated fibroblasts (CAFs), the predominant stromal cell type in the breast tumour microenvironment, may contribute to cancer progression through interaction with tumour cells. Nonetheless, little is known about the details of the underlying mechanism. Here we found that interaction of interleukin 32 (IL32) with integrin β3 (encoded by ITGB3; a member of the integrin family) mediating the cross-talk between CAFs and breast cancer cells plays a crucial role in CAF-induced breast tumour invasiveness. IL32, an 'RGD' motif-containing cytokine, was found to be abundantly expressed in CAFs. Integrin β3 turned out to be up-regulated in breast cancer cells during epithelial-mesenchymal transition (EMT). CAF-derived IL32 specifically bound to integrin β3 through the RGD motif, thus activating intracellular downstream p38 MAPK signalling in breast cancer cells. This signalling increased the expression of EMT markers (fibronectin, N-cadherin, and vimentin) and promoted tumour cell invasion. Counteracting IL32 activity, a knockdown of IL32 or integrin β3 led to specific inactivation of p38 MAPK signalling in tumour cells. Blockage of the p38 MAPK pathway also diminished IL32-induced expression of EMT markers and breast cancer cell invasion and metastasis. Thus, our data indicate that CAF-secreted IL32 promotes breast cancer cell invasion and metastasis via integrin β3-p38 MAPK signalling.

Transcriptional cofactors Ski and SnoN are major regulators of the TGF-β/Smad signaling pathway in health and disease

The transforming growth factor-β (TGF-β) family plays major pleiotropic roles by regulating many physiological processes in development and tissue homeostasis. The TGF-β signaling pathway outcome relies on the control of the spatial and temporal expression of >500 genes, which depend on the functions of the Smad protein along with those of diverse modulators of this signaling pathway, such as transcriptional factors and cofactors. Ski (Sloan-Kettering Institute) and SnoN (Ski novel) are Smad-interacting proteins that negatively regulate the TGF-β signaling pathway by disrupting the formation of R-Smad/Smad4 complexes, as well as by inhibiting Smad association with the p300/CBP coactivators. The Ski and SnoN transcriptional cofactors recruit diverse corepressors and histone deacetylases to repress gene transcription. The TGF-β/Smad pathway and coregulators Ski and SnoN clearly regulate each other through several positive and negative feedback mechanisms. Thus, these cross-regulatory processes finely modify the TGF-β signaling outcome as they control the magnitude and duration of the TGF-β signals. As a result, any alteration in these regulatory mechanisms may lead to disease development. Therefore, the design of targeted therapies to exert tight control of the levels of negative modulators of the TGF-β pathway, such as Ski and SnoN, is critical to restore cell homeostasis under the specific pathological conditions in which these cofactors are deregulated, such as fibrosis and cancer.

Proteins that repress molecular signaling through the transforming growth factor-beta (TGF-β) pathway offer promising targets for treating cancer and fibrosis. Marina Macías-Silva and colleagues from the National Autonomous University of Mexico in Mexico City review the ways in which a pair of proteins, called Ski and SnoN, interact with downstream mediators of TGF-β to inhibit the effects of this master growth factor. Aberrant levels of Ski and SnoN have been linked to diverse range of diseases involving cell proliferation run amok, and therapies that regulate the expression of these proteins could help normalize TGF-β signaling to healthier physiological levels. For decades, drug companies have tried to target the TGF-β pathway, with limited success. Altering the activity of these repressors instead could provide a roundabout way of remedying pathogenic TGF-β activity in fibrosis and oncology.

Silencing of c-Ski augments TGF-b1-induced epithelial-mesenchymal transition in cardiomyocyte H9C2 cells

BACKGROUND

The shRNA lentiviral vector was constructed to silence c-Ski expression in cardiac mus- cle cells, with the aim of exploring the role of c-Ski in transforming growth factor b1 (TGF-b1)-induced epithelial-mesenchymal transitions (EMT) in H9C2 cells.

METHODS

Real-time polymerase chain reaction (RT-PCR) and western blot were used to detect c-Ski ex- pression at protein and messenger ribonucleic acid (mRNA) levels in 5 different cell lines. Then, lentiviral vector was constructed to silence or overexpress c-Ski in H9C2 cells. MTT and/or soft agar assay and tran- swell assay were used to detect cell proliferation and migration, respectively. The expression levels of c-Ski under different concentrations of TGF-b1 stimulation were detected by RT-qPCR and immunocytochemi- cal analysis. In the presence or absence of TGF-b1 stimulation, the proteins' expression levels of a-SMA, FN and E-cadherin, which are closely correlated with the process of EMT, were measured by western blot after c-Ski silencing or overexpression. Meanwhile, the effect of c-Ski on Samd3 phosphorylation with TGF-b1 stimulation was investigated.

RESULTS

There is a high expression of c-Ski at protein and mRNA levels in H9C2 cell line, which first demonstrated the presence of c-Ski expression in H9C2 cells. Overexpression of c-Ski significantly increased H9C2 cell proliferation. The ability of c-Ski gene silencing to suppress cell proliferation was gradually enhanced, and inhibition efficiency was the highest after 6 to 7 d of transfection. Moreover, H9C2 cells with c-Ski knockdown gained significantly aggressive invasive potential when compared with the control group. TGF-b1 stimulation could dose-independently reduce c-Ski expression in H9C2 cells and lead to obvious down-regulated expression of E-cadherin. Interestingly, c-Ski could restore E-cadherin expression while suppressing a-SMA and/or FN expression stimulated by TGF-b1. How- ever, shRNA-induced c-Ski knockdown aggravated only the TGF-b1-induced EMT. Moreover, c-Ski- -shRNA also promoted the phosphorylation of Samd3 induced by TGF-b1.

CONCLUSIONS

c-Ski expression in cardiac muscle cells could be down-regulated by TGF-b1. Silencing of c-Ski gene was accompanied by down-regulation of E-cadherin, up-regulation of a-SMA and/or FN and Smad3 phosphorylation induced by TGF-b1, promoting EMT process. Therefore, c-Ski may be closely associated with TGF-b1-induced EMT and play an important role in cardiac fibrosis develop- ment and progression.

Primed atypical ductal hyperplasia-associated fibroblasts promote cell growth and polarity changes of transformed epithelium-like breast cancer MCF-7 cells via miR-200b/c-IKKβ signaling

Cancer-associated fibroblasts (CAFs) support tumorigenesis by stimulating cancer cell proliferation, and invasion, but how the premalignant stromal fibroblasts trigger epithelial changes remain unclear. We demonstrate that atypical ductal hyperplasia-associated fibroblasts (AHFs) are one kind of activated fibroblasts and stimulate cell growth and polarity change of epithelium-like tumor cell MCF-7 as CAFs-like fibroblasts. Microarray shows miR-200b and miR-200c are downregulated during AHFs and CAFs, and contribute to stromal fibroblast activity. Additionally, miR-200b/c with target gene IKKβ (inhibitor of nuclear factor kappa-B kinase β) control PAI-1 (plasminogen activator inhibitor-1) expression to regulate growth and polarity changes of MCF-7 cells through NF-κB pathway. Exploring the difference of AHFs in premalignant transformation is crucial for understanding the pathobiology of breast cancer progression.

Nuclear Drosha enhances cell invasion via an EGFR-ERK1/2-MMP7 signaling pathway induced by dysregulated miRNA-622/197 and their targets LAMC2 and CD82 in gastric cancer

Drosha is an RNA III-like enzyme that has an aberrant expression in some tumors. Our previous studies showed the aberrant Drosha in gastric tumors. However, the roles of nuclear Drosha, the main regulator of microRNA (miRNA) biogenesis, in gastric cancer (GC) progression remain poorly understood. In this study, we demonstrated that nuclear Drosha is significantly associated with cell invasion of GC and that Drosha silence impedes the tumor invasion. Knockdown of Drosha led to a set of dysregulated miRNAs in GC cells. Multiple targets of these miRNAs were the members in cell migration, invasion and metastasis-associated signaling (e.g. ECM-receptor interaction, focal adhesion, p53 signaling and MAPK signaling pathway) revealed by bioinformatics analysis. LAMC2 (a key element of ECM-receptor signaling) and CD82 (a suppressor of p53 signaling) are the targets of miR-622 and miR-197, respectively. High levels of LAMC2 and low levels of CD82 were significantly related to the worse outcome for GC patients. Furthermore, overexpression of LAMC2 and knockdown of CD82 markedly promoted GC cell invasion and activated EGFR/ERK1/2-MMP7 signaling via upregulation of the expression of phosphorylated (p)-EGFR, p-ERK1/2 and MMP7. Our findings suggest that nuclear Drosha potentially has a role in the development of GC.

Twist promotes reprogramming of glucose metabolism in breast cancer cells through PI3K/AKT and p53 signaling pathways

Twist, a key regulator of epithelial-mesenchymal transition (EMT), plays an important role in the development of a tumorigenic phenotype. Energy metabolism reprogramming (EMR), a newly discovered hallmark of cancer cells, potentiates cancer cell proliferation, survival, and invasion. Currently little is known about the effects of Twist on tumor EMR. In this study, we found that glucose consumption and lactate production were increased and mitochondrial mass was decreased in Twist-overexpressing MCF10A mammary epithelial cells compared with vector-expressing MCF10A cells. Moreover, these Twist-induced phenotypic changes were augmented by hypoxia. The expression of some glucose metabolism-related genes such as PKM2, LDHA, and G6PD was also found to be upregulated. Mechanistically, activated β1-integrin/FAK/PI3K/AKT/mTOR and suppressed P53 signaling were responsible for the observed EMR. Knockdown of Twist reversed the effects of Twist on EMR in Twist-overexpressing MCF10A cells and Twist-positive breast cancer cells. Furthermore, blockage of the β1-integrin/FAK/PI3K/AKT/mTOR pathway by siRNA or specific chemical inhibitors, or rescue of p53 activation can partially reverse the switch of glucose metabolism and inhibit the migration of Twist-overexpressing MCF10A cells and Twist-positive breast cancer cells. Thus, our data suggest that Twist promotes reprogramming of glucose metabolism in MCF10A-Twist cells and Twist-positive breast cancer cells via activation of the β1-integrin/FAK/PI3K/AKT/mTOR pathway and inhibition of the p53 pathway. Our study provides new insight into EMR.

Oxidized ATM promotes abnormal proliferation of breast CAFs through maintaining intracellular redox homeostasis and activating the PI3K-AKT, MEK-ERK, and Wnt-β-catenin signaling pathways

Abnormal proliferation is one characteristic of cancer-associated fibroblasts (CAFs), which play a key role in tumorigenesis and tumor progression. Oxidative stress (OS) is the root cause of CAFs abnormal proliferation. ATM (ataxia-telangiectasia mutated protein kinase), an important redox sensor, is involved in DNA damage response and cellular homeostasis. Whether and how oxidized ATM regulating CAFs proliferation remains unclear. In this study, we show that there is a high level of oxidized ATM in breast CAFs in the absence of double-strand breaks (DSBs) and that oxidized ATM plays a critical role in CAFs proliferation. The effect of oxidized ATM on CAFs proliferation is mediated by its regulation of cellular redox balance and the activity of the ERK, PI3K-AKT, and Wnt signaling pathways. Treating cells with antioxidant N-acetyl-cysteine (NAC) partially rescues the proliferation defect of the breast CAFs caused by ATM deficiency. Administrating cells with individual or a combination of specific inhibitors of the ERK, PI3K-AKT, and Wnt signaling pathways mimics the effect of ATM deficiency on breast CAF proliferation. This is mainly ascribed to the β-catenin suppression and down-regulation of c-Myc, thus further leading to the decreased cyclinD1, cyclinE, and E2F1 expression and the enhanced p21(Cip1) level. Our results reveal an important role of oxidized ATM in the regulation of the abnormal proliferation of breast CAFs. Oxidized ATM could serve as a potential target for treating breast cancer.

Twist induces epithelial-mesenchymal transition and cell motility in breast cancer via ITGB1-FAK/ILK signaling axis and its associated downstream network

Twist, a highly conserved basic Helix-Loop-Helix transcription factor, functions as a major regulator of epithelial-mesenchymal transition (EMT) and tumor metastasis. In different cell models, signaling pathways such as TGF-β, MAPK/ERK, WNT, AKT, JAK/STAT, Notch, and P53 have also been shown to play key roles in the EMT process, yet little is known about the signaling pathways regulated by Twist in tumor cells. Using iTRAQ-labeling combined with 2D LC-MS/MS analysis, we identified 194 proteins with significant changes of expression in MCF10A-Twist cells. These proteins reportedly play roles in EMT, cell junction organization, cell adhesion, and cell migration and invasion. ECM-receptor interaction, MAPK, PI3K/AKT, P53 and WNT signaling were found to be aberrantly activated in MCF10A-Twist cells. Ingenuity Pathways Analysis showed that integrin β1 (ITGB1) acts as a core regulator in linking integrin-linked kinase (ILK), Focal-adhesion kinase (FAK), MAPK/ERK, PI3K/AKT, and WNT signaling. Increased Twist and ITGB1 are associated with breast tumor progression. Twist transcriptionally regulates ITGB1 expression. Over-expression of ITGB1 or Twist in MCF10A led to EMT, activation of FAK/ILK, MAPK/ERK, PI3K/AKT, and WNT signaling. Knockdown of Twist or ITGB1 in BT549 and Hs578T cells decreased activity of FAK, ILK, and their downstream signaling, thus specifically impeding EMT and cell invasion. Knocking down ILK or inhibiting FAK, MAPK/ERK, or PI3K/AKT signaling also suppressed Twist-driven EMT and cell invasion. Thus, the Twist-ITGB1-FAK/ILK pathway and their downstream signaling network dictate the Twist-induced EMT process in human mammary epithelial cells and breast cancer cells.

LncRNA-Hh Strengthen Cancer Stem Cells Generation in Twist-Positive Breast Cancer via Activation of Hedgehog Signaling Pathway

Cancer stem cells (CSCs) are a subpopulation of neoplastic cells with self-renewal capacity and limitless proliferative potential as well as high invasion and migration capacity. These cells are commonly associated with epithelial-mesenchymal transition (EMT), which is also critical for tumor metastasis. Recent studies illustrate a direct link between EMT and stemness of cancer cells. Long non-coding RNAs (lncRNAs) have emerged as important new players in the regulation of multiple cellular processes in various diseases. To date, the role of lncRNAs in EMT-associated CSC stemness acquisition and maintenance remains unclear. In this study, we discovered that a set of lncRNAs were dysregulated in Twist-positive mammosphere cells using lncRNA microarray analysis. Multiple lncRNAs-associated canonical signaling pathways were identified via bioinformatics analysis. Especially, the Shh-GLI1 pathway associated lncRNA-Hh, transcriptionally regulated by Twist, directly targets GAS1 to stimulate the activation of hedgehog signaling (Hh). The activated Hh increases GLI1 expression, and enhances the expression of SOX2 and OCT4 to play a regulatory role in CSC maintenance. Thus, the mammosphere-formation efficiency (MFE) and the self-renewal capacity in vitro, and oncogenicity in vivo in Twist-positive breast cancer cells are elevated. lncRNA-Hh silence in Twist-positive breast cells attenuates the activated Shh-GLI1 signaling and decreases the CSC-associated SOX and OCT4 levels, thus reduces the MFE and tumorigenesis of transplanted tumor. Our results reveal that lncRNAs function as an important regulator endowing Twist-induced EMT cells to gain the CSC-like stemness properties.

Stromal miR-200s contribute to breast cancer cell invasion through CAF activation and ECM remodeling

The activation of cancer-associated fibroblasts (CAFs) is a key event in tumor progression, and alternative extracellular matrix (ECM) proteins derived from CAFs induce ECM remodeling and cancer cell invasion. Here we found that miR-200 s, which are generally downregulated in activated CAFs in breast cancer tissues and in normal fibroblasts (NFs) activated by breast cancer cells, are direct mediators of NF reprogramming into CAFs and of ECM remodeling. NFs with downregulated miR-200 s displayed the traits of activated CAFs, including accelerated migration and invasion. Ectopic expression of miR-200 s in CAFs at least partially restored the phenotypes of NFs. CAF activation may be governed by the targets of miR-200 s, Fli-1 and TCF12, which are responsible for cell development and differentiation; Fli-1 and TCF12 were obviously elevated in CAFs. Furthermore, miR-200 s and their targets influenced collagen contraction by CAFs. The upregulation of fibronectin and lysyl oxidase directly by miR-200 or indirectly through Fli-1 or TCF12 contributed to ECM remodeling, triggering the invasion and metastasis of breast cancer cells both in vitro and vivo. Thus, these data provide important and novel insights into breast CAF activation and ECM remodeling, which trigger tumor cell invasion.

Stearoyl-CoA desaturase 1 and paracrine diffusible signals have a major role in the promotion of breast cancer cell migration induced by cancer-associated fibroblasts

Background:

Despite the recognised contribution of the stroma to breast cancer development and progression, the effective targeting of the tumor microenvironment remains a challenge to be addressed. We previously reported that normal fibroblasts (NFs) and, notably, breast cancer-associated fibroblasts (CAFs) induced epithelial-to-mesenchymal transition and increases in cell membrane fluidity and migration in well- (MCF-7) and poorly-differentiated (MDA-MB-231) breast cancer cells. This study was designed to better define the role played, especially by CAFs, in promoting breast tumor cell migration.

Methods:

Fibroblast/breast cancer cell co-cultures were set up to investigate the influence of NFs and CAFs on gene and protein expression of Stearoyl-CoA desaturase 1 (SCD1), the main enzyme regulating membrane fluidity, as well as on the protein level and activity of its transcription factor, the sterol regulatory element-binding protein 1 (SREBP1), in MCF-7 and MDA-MB-231 cells. To assess the role of SREBP1 in the regulation of SCD1 expression, the desaturase levels were also determined in tumor cells treated with an SREBP1 inhibitor. Migration was evaluated by wound-healing assay in SCD1-inhibited (by small-interfering RNA (siRNA) or pharmacologically) cancer cells and the effect of CAF-conditioned medium was also assessed. To define the role of stroma-derived signals in cancer cell migration speed, cell-tracking analysis was performed in the presence of neutralising antibodies to hepatocyte growth factor, transforming growth factor-β or basic fibroblast growth factor.

Results:

A two to three fold increase in SCD1 mRNA and protein expression has been induced, particularly by CAFs, in the two cancer cell lines that appear to be dependent on SREBP1 activity in MCF-7 but not in MDA-MB-231 cells. Both siRNA-mediated and pharmacological inhibition of SCD1 impaired tumor cells migration, also when promoted by CAF-released soluble factors. Fibroblast-triggered increase in cancer cell migration speed was markedly reduced or abolished by neutralising the above growth factors.

Conclusion:

These results provide further insights in understanding the role of CAFs in promoting tumor cell migration, which may help to design new stroma-based therapeutic strategies.

PLCε knockdown inhibits prostate cancer cell proliferation via suppression of Notch signalling and nuclear translocation of the androgen receptor

Phospholipase Cε (PLCε), a key regulator of diverse cellular functions, has been implicated in various malignancies. Indeed, PLCε functions include cell proliferation, apoptosis and malignant transformation. Here, we show that PLCε expression is elevated in prostate cancer (PCa) tissues compared to benign prostate tissues. Furthermore, PLCε depletion using an adenovirally delivered shRNA significantly decreased cell growth and colony formation, arresting the PC3 and LNCaP cell lines in the S phase of the cell cycle. We also observed that PLCε was significantly correlated with Notch1 and androgen receptor (AR). Additionally, we demonstrate that the activation of both the Notch and AR signalling pathways is involved in PLCε-mediated oncogenic effects in PCa. Our findings suggest that PLCε is a putative oncogene and prognostic marker, potentially representing a novel therapeutic target for PCa.

SnoN as a novel negative regulator of TGF-β/Smad signaling: a target for tailoring organ fibrosis

Remodeling of the extracellular matrix is beneficial during the acute wound healing stage following tissue injury. In the short term, resident fibroblasts and myofibroblasts regulate the matrix remodeling process through production of matricellular protein components that provide structural support to the damaged tissue. This process is largely governed by the transforming growth factor-β1 (TGF-β1) pathway, a critical mediator of the remodeling process. In the long term, chronic activation of the TGF-β1 pathway promotes excessive synthesis and deposition of matrix proteins, including fibrillar collagens, which ultimately leads to organ failure. SnoN (and its alternatively-spliced isoforms SnoN2, SnoA, and SnoI) is one of four members of a family of negative regulators of TGF-β1 signaling that includes Ski and functional Smad-suppressing elements on chromosomes 15 and 18. SnoN has been shown to be structurally and functionally similar to Ski and has been demonstrated to directly interact with Ski to abrogate gene expression. Despite this, little progress has been made in delineating a specific role for SnoN in the regulation of myofibroblast phenotype and function. This review outlines the current body of knowledge of what we refer to as the “Ski-Sno superfamily,” with a focus on the structural and functional importance of SnoN in mediating the fibrotic response by myofibroblasts following tissue injury.

Array CGH analysis identifies two distinct subgroups of primary angiosarcoma of bone

Molecular genetic studies on vascular tumors are rare. Recently, possible involvement of MYC and KDR has been documented in a subset of angiosarcomas of soft tissue. We performed a cytogenetic analysis of primary angiosarcomas of bone (n = 13) and soft tissue (n = 5) using high density array-comparative genomic hybridization (array-CGH). Regions of interest were validated by fluorescence in situ hybridization (FISH). Antibodies for candidate genes (SKI, MYC, KDR, and MAPK9) were selected and immunohistochemistry was performed. Six angiosarcomas of bone and four angiosarcomas of soft tissue showed chromosomal losses, gains, and high level amplifications. Cluster analysis identified two groups: a group with a complex genetic profile and a group with only few genetic aberrations. Five regions of interest were selected, which were located at chromosome bands 1p36.23, 2q32-34, 5q35, 8q24, and 17q21.32-24.2. Interphase FISH confirmed the high-level amplifications. Immunohistochemical analysis showed high expression of MYC (16/60), MAPK9 (63/69), and SKI (52/62). There were no differences between the two groups with regards to location, immunohistochemical expression nor survival. In summary, we identified two subgroups of angiosarcoma: those with few or no gross aberrations and those which show numerous genetic aberrations consisting of chromosomal losses, gains and high level amplifications or complex aberrations. The most common finding was amplification of 2q and 17q in both angiosarcoma of bone and soft tissue, suggesting overlap in tumorigenesis irrespective of their location. We show MYC amplification in primary angiosarcoma indicating this is not entirely specific for radiation-induced angiosarcoma.

GPER mediates enhanced cell viability and motility via non-genomic signaling induced by 17β-estradiol in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) is an aggressive breast cancer with a generally poor prognosis. Due to lack of specific targets for its treatment, an efficient therapy is needed. G protein-coupled estrogen receptor (GPER), a novel estrogen receptor, has been reported to be expressed in TNBC tissues. In this study, we investigated the effects of blocking non-genomic signaling mediated by the estrogen/GPER pathway on cell viability and motility in the TNBC cells. GPER was strongly expressed in the TNBC cell lines MDA-MB-468 and MDA-MB-436, and the estrogen-mediated non-genomic ERK signaling activated by GPER was involved in cell viability and motility of TNBC cells. Treatment with 17β-estradiol (E2), the GPER-specific agonist G-1 and tamoxifen (TAM) led to rapid activation of p-ERK1/2, but not p-Akt. Moreover, estrogen/GPER/ERK signaling was involved in increasing cell growth, survival, and migration/invasion by upregulating expression of cyclinA, cyclinD1, Bcl-2, and c-fos associated with the cell cycle, proliferation, and apoptosis. Immunohistochemical analysis of TNBC specimens showed a significantly different staining of p-ERK1/2 between GPER-positive tissues (58/66, 87.9%) and GPER-negative tissues (13/30, 43.3%). The positivity of GPER and p-ERK1/2 displayed a strong association with large tumor size and poor clinical stage, indicating that GPER/ERK signaling might also contribute to tumor progression in TNBC patients which corresponded with in vitro experimental data. Our findings suggest that inhibition of estrogen/GPER/ERK signaling represents a novel targeted therapy in TNBC.

c-Ski activates cancer-associated fibroblasts to regulate breast cancer cell invasion

Aberrant expression of c-Ski oncoprotein in some tumor cells has been shown to be associated with cancer development. However, the role of c-Ski in cancer-associated fibroblasts (CAFs) of tumor microenvironment has not been characterized. In the current study, we found that c-Ski is highly expressed in CAFs derived from breast carcinoma microenvironment and this CAF-associated c-Ski expression is associated with invasion and metastasis of human breast tumors. We showed that c-Ski overexpression in immortalized breast normal fibroblasts (NFs) induces conversion to breast CAFs by repressing p53 and thereby upregulating SDF-1 in NFs. SDF-1 treatment or p53 knockdown in NFs had similar effects on the activation of NFs as c-Ski overexpression. The c-Ski-activated CAFs show increased proliferation, migration, invasion and contraction compared with NFs. Furthermore, c-Ski-activated CAFs facilitated the migration and invasion of MDA-MB-231 breast cancer cells. Our data suggest that c-Ski is an important regulator in the activation of CAFs and may serve as a potential therapeutic target to block breast cancer progression.