Tumour-derived exosomal lncRNA-SOX2OT promotes bone metastasis of non-small cell lung cancer by targeting the miRNA-194-5p/RAC1 signalling axis in osteoclasts

Bone is a frequent metastatic site of non-small cell lung cancer (NSCLC), and bone metastasis (BoM) presents significant challenges for patient survival and quality of life. Osteolytic BoM is characterised by aberrant differentiation and malfunction of osteoclasts through modulation of the TGF-β/pTHrP/RANKL signalling pathway, but its upstream regulatory mechanism is unclear. In this study, we found that lncRNA-SOX2OT was highly accumulated in exosomes derived from the peripheral blood of NSCLC patients with BoM and that patients with higher expression of exosomal lncRNA-SOX2OT had significantly shorter overall survival. Additionally, exosomal lncRNA-SOX2OT derived from NSCLC cells promoted cell invasion and migration in vitro, as well as BoM in vivo. Mechanistically, we discovered that NSCLC cell-derived exosomal lncRNA-SOX2OT modulated osteoclast differentiation and stimulated BoM by targeting the miRNA-194-5p/RAC1 signalling axis and TGF-β/pTHrP/RANKL signalling pathway in osteoclasts. In conclusion, exosomal lncRNA-SOX2OT plays a crucial role in promoting BoM and may serve as a promising prognostic biomarker and treatment target in metastatic NSCLC.Subject terms: Non-small-cell lung cancer, Oncogenesis     

Exosomal miR-1260b derived from non-small cell lung cancer promotes tumor metastasis through the inhibition of HIPK2

Tumor-derived exosomes (TEXs) contain enriched miRNAs, and exosomal miRNAs can affect tumor growth, including cell proliferation, metastasis, and drug resistance through cell-to-cell communication. We investigated the role of exosomal miR-1260b derived from non-small cell lung cancer (NSCLC) in tumor progression. Exosomal miR-1260b induced angiogenesis by targeting homeodomain-interacting protein kinase-2 (HIPK2) in human umbilical vein endothelial cells (HUVECs). Furthermore, exosomal miR-1260b or suppression of HIPK2 led to enhanced cellular mobility and cisplatin resistance in NSCLC cells. In patients with NSCLC, the level of HIPK2 was significantly lower in tumor tissues than in normal lung tissues, while that of miR-1260b was higher in tumor tissues. HIPK2 and miR-1260b expression showed an inverse correlation, and this correlation was strong in distant metastasis. Finally, the expression level of exosomal miR-1260b in plasma was higher in patients with NSCLC than in healthy individuals, and higher levels of exosomal miR-1260b were associated with high-grade disease, metastasis, and poor survival. In conclusion, exosomal miR-1260b can promote angiogenesis in HUVECs and metastasis of NSCLC by regulating HIPK2 and may serve as a prognostic marker for lung cancers.Subject terms: Non-small-cell lung cancer, Metastasis, miRNAs     

Exosomal miR-146a-5p and miR-155-5p promote CXCL12/CXCR7-induced metastasis of colorectal cancer by crosstalk with cancer-associated fibroblasts

C-X-C motif chemokine receptor 7 (CXCR7) is a newly discovered atypical chemokine receptor that binds to C-X-C motif chemokine ligand 12 (CXCL12) with higher affinity than CXCR4 and is associated with the metastasis of colorectal cancer (CRC). Cancer-associated fibroblasts (CAFs) have been known to promote tumor progression. However, whether CAFs are involved in CXCR7-mediated metastasis of CRC remains elusive. We found a significant positive correlation between CXCR7 expression and CAF activation markers in colonic tissues from clinical specimens and in villin-CXCR7 transgenic mice. RNA sequencing revealed a coordinated increase in the levels of miR-146a-5p and miR-155-5p in CXCR7-overexpressing CRC cells and their exosomes. Importantly, these CRC cell-derived miR-146a-5p and miR-155-5p could be uptaken by CAFs via exosomes and promote the activation of CAFs through JAK2–STAT3/NF-κB signaling by targeting suppressor of cytokine signaling 1 (SOCS1) and zinc finger and BTB domain containing 2 (ZBTB2). Reciprocally, activated CAFs further potently enhanced the invasive capacity of CRC cells. Mechanistically, CAFs transfected with miR-146a-5p and miR-155-5p exhibited a robust increase in the levels of inflammatory cytokines interleukin-6, tumor necrosis factor-α, transforming growth factor-β, and CXCL12, which trigger the epithelial–mesenchymal transition and pro-metastatic switch of CRC cells. More importantly, the activation of CAFs by miR-146a-5p and miR-155-5p facilitated tumor formation and lung metastasis of CRC in vivo using tumor xenograft models. Our work provides novel insights into CXCR7-mediated CRC metastasis from tumor–stroma interaction and serum exosomal miR-146a-5p and miR-155-5p could serve as potential biomarkers and therapeutic targets for inhibiting CRC metastasis.Subject terms: Cancer microenvironment, Colon cancer     

Cancer-secreted exosomal miR-21-5p induces angiogenesis and vascular permeability by targeting KRIT1

Cancer-secreted exosomes are critical mediators of cancer-host crosstalk. In the present study, we showed the delivery of miR-21-5p from colorectal cancer (CRC) cells to endothelial cells via exosomes increased the amount of miR-21-5p in recipient cells. MiR-21-5p suppressed Krev interaction trapped protein 1 (KRIT1) in recipient HUVECs and subsequently activated β-catenin signaling pathway and increased their downstream targets VEGFa and Ccnd1, which consequently promoted angiogenesis and vascular permeability in CRC. A strong inverse correlation between miR-21-5p and KRIT1 expression levels was observed in CRC-adjacent vessels. Furthermore, miR-21-5p expression in circulating exosomes was markedly higher in CRC patients than in healthy donors. Thus, our data suggest that exosomal miR-21-5p is involved in angiogenesis and vascular permeability in CRC and may be used as a potential new therapeutic target.Subject terms: Cancer microenvironment, Colon cancer     

Tumor-derived exosomal miR-3157-3p promotes angiogenesis,vascular permeability and metastasis by targeting TIMP/KLF2 in non-small cell lung cancer

Metastasis is the main cause of death in patients with advanced lung cancer. The exosomes released by cancer cells create tumor microenvironment, and then accelerate tumor metastasis. Cancer-derived exosomes are considered to be the main driving force for metastasis niche formation at foreign sites, but the mechanism in Non-small cell lung carcinoma (NSCLC) is unclear. In metastatic NSCLC patients, the expression level of miR-3157-3p in circulating exosomes was significantly higher than that of non-metastatic NSCLC patients. Here, we found that miR-3157-3p can be transferred from NSCLC cells to vascular endothelial cells through exosomes. Our work indicates that exosome miR-3157-3p is involved in the formation of pre-metastatic niche formation before tumor metastasis and may be used as a blood-based biomarker for NSCLC metastasis. Exosome miR-3157-3p has regulated the expression of VEGF/MMP2/MMP9 and occludin in endothelial cells by targeting TIMP/KLF2, thereby promoted angiogenesis and increased vascular permeability. In addition, exosome miR-3157-3p promoted the metastasis of NSCLC in vivo.Subject terms: Cancer microenvironment, Non-small-cell lung cancer     

Oligodendrocyte Precursor Cells Support Blood-Brain Barrier Integrity via TGF-β Signaling

Trophic coupling between cerebral endothelium and their neighboring cells is required for the development and maintenance of blood-brain barrier (BBB) function. Here we report that oligodendrocyte precursor cells (OPCs) secrete soluble factor TGF-β1 to support BBB integrity. Firstly, we prepared conditioned media from OPC cultures and added them to cerebral endothelial cultures. Our pharmacological experiments showed that OPC-conditioned media increased expressions of tight-junction proteins and decreased in vitro BBB permeability by activating TGB-β-receptor-MEK/ERK signaling pathway. Secondly, our immuno-electron microscopic observation revealed that in neonatal mouse brains, OPCs attach to cerebral endothelial cells via basal lamina. And finally, we developed a novel transgenic mouse line that TGF-β1 is knocked down specifically in OPCs. Neonates of these OPC-specific TGF-β1 deficient mice (OPC-specific TGF-β1 partial KO mice: Pdgfra^Cre/Tgfb1^flox/wt mice or OPC-specific TGF-β1 total KO mice: Pdgfra^Cre/Tgfb1^flox/flox mice) exhibited cerebral hemorrhage and loss of BBB function. Taken together, our current study demonstrates that OPCs increase BBB tightness by upregulating tight junction proteins via TGF-β signaling. Although astrocytes and pericytes are well-known regulators of BBB maturation and maintenance, these findings indicate that OPCs also play a pivotal role in promoting BBB integrity.     

Organotropic metastasis: role of tumor exosomes

A recent paper in Nature shows that tumor exosomes expressing unique integrins can determine organotropic metastasis by preparing pre-metastatic niche through their integrins-mediated fusion with and fertilization of organ-specific resident cells.Tumor metastasis is a critical step in malignant progression of tumors and has been implicated in the failure of most cancer therapeutics. One salient feature of metastasis is that some types of cancer cells preferentially colonize and metastasize to specific organs, under the control of a range of cellular and molecular programs¹. Many studies focus largely on identifying cell-intrinsic determinants of such organotropic metastasis, including genes and chemokine receptors expressed on cancer cells². The adhesion and extracellular matrixc molecules, such as integrins, tenascin and periostin, have been also shown to promote colonization of metastatic cancer cells³. In 2005, Dr Lyden and colleagues proposed a term of pre-metastatic niche to describe the phenomenon that primary tumor could promote its own metastasis by recruiting bone marrow-derived cells to the distant organ and establish supportive metastatic environments⁴. Besides, tumor-derived soluble factors such as lysyl oxidase⁵ have been also reported to induce organ-specific metastasis by formation of pre-metastatic niche in certain sites. However, the exact mechanism for metastatic organotropism is still unclear. In recent years, tumor-derived exosomes have been demonstrated to promote cancer progression⁶. Exosomes are small membrane-bound vesicles (30-100 nm) containing functional biomolecules (including proteins, RNA, DNA and lipids) that can be horizontally transferred to recipient cells⁷. For example, brain astrocyte-derived exosomes can promote the outgrowth of brain metastatic cancer cells by transferring PTEN-targeting microRNA-19a to these cancer cells⁸. Nevertheless, whether molecules present on tumor exosomes can determine organ-specific metastasis is an unresolved question.Lyden and colleagues in their recent Nature paper gave the answer that tumor exosome integrins can determine organotropic metastasis by fusing with organ-specific resident cells to establish pre-metastatic niche through activating Src phosphorylation and pro-inflammatory S100 expression⁹ (Figure 1). The authors isolated exosomes from organotropic human and mouse breast and pancreatic cancer cell lines known to primarily metastasize to the lung, liver, or both⁹. Then, they retro-orbitally injected these near infrared (NIR) or red fluorescently labeled exosomes into nude mice and quantified exosome biodistribution and uptake in distant organs after 24 h by NIR whole-lung imaging and confocal microscopy. Using this approach, they observed that exosomes from different cancer models selectively interact with the same future metastatic organs as their cell of origin. Thus, the authors proposed that exosomes could promote organ-specific metastasis. To test exosome-mediated education of target organs functionally, they injected luciferase-expressing 4175-LuT (LuT, Lung-tropic) or 1833-BoT (BoT, bone-tropic) cells into 4175-LuT or 1833-BoT exosome-educated mice, and found that education with 4175-LuT-derived exosomes increased the lung metastatic capacity of 4175-LuT tumors, and interestingly, even significantly redirected the bone-tropic 1833-BoT cells to disseminate in the lung. These observations suggested that certain type of tumor exosomes can prepare pre-metastatic niches to facilitate organ-specific metastasis and redirect metastatic distribution even for cancer cells poorly capable of metastasizing to these sites.Open in a separate windowFigure 1Tumor exosomes direct organ-specific metastasis via integrins. Tumor-derived exosomes transport proteins, nucleic acids and lipids to specific organ and fuse with resident cells, which can prepare distant organ site as pre-metastatic niche. Lyden and colleagues⁹ report that exosomes derived from different type of cancer cells can display different integrin proteins on their surface; ITGα₆β₄- and ITGα₆β₁-expressing exosomes preferentially interact with fibroblasts and epithelial cells in lung, and ITGα_vβ₅-expressing exosomes preferentially fuse with Kupffer cells in liver. Once uptaken, tumor exosomes induce cellular changes (Src activation and pro-inflammatory S100 gene expression) in the target organ, thus promoting cancer cell colonization and organ-specific metastasis.To further dissect the molecular mechanisms involved in organ-specific metastasis, through quantitative mass spectrometry of lung-, liver- and brain-tropic exosomes, they identified integrins (ITGs) — the most highly represented cell adhesion receptor proteins in exosomes — as determinants of metastatic organotropism. Subsequent analysis showed that lung-tropic exosomes expressing ITGα₆β₄ and ITGα₆β₁ could interact with S100A4-positive fibroblasts and surfactant protein C-positive epithelial cells in laminin-rich lung microenvironments, ITGα_vβ₅-expressing pancreatic exosomes co-localized with F4/80⁺ macrophages and fused with Kupffer cells in fibronectin-rich liver niches, and brain-tropic 831-BrT exosomes interacted mainly with CD31⁺ brain endothelial cells. Furthermore, inhibiting the exosomal integrins ITGβ₄ and ITGβ₅ expression via short hairpin RNAs or blocking their binding by HYD-1/RGD peptides markedly reduced exosome uptake as well as lung and liver metastasis, respectively. Thus, the authors demonstrated that certain exosomal integrins govern organ-specific metastasis by fusing with target cells in an organ-specific manner. When using RNA sequencing to analyze the gene expression in distinct cells targeted by exosomes, they found that exosomal ITGs could prominently upregulate pro-inflammatory S100 gene expression (i.e., several S100 genes (S100A4, -A6, -A10, -A11, -A13 and -A16) were upregulated in 4175-LuT exosome-educated WI-38 fibroblasts; S100A8 and S100P were upregulated in BxPC-3-LiT exosome-educated Kupffer cells). Moreover, exosomal ITGβ₄ uptake could increase Src or phosphorylated Src (pSrc) levels in resident cells. S100 proteins promote metastasis¹⁰, and ITGα₆β₄ can active Src and S100A4 expression¹¹. Taken together, the mechanisms for exosomal integrins in promoting tumor organotropic metastasis in this Nature paper⁹ may be summarized as follows: (1) promotion of adhesion by fusing with specific resident cells; (2) activation of Src signaling pathways and inflammatory responses (pro-inflammatory S100 gene expression) in these target cells, thus preparing favorable pre-metastatic niche for further metastasis (Figure 1).Finally, their clinical data showed that ITGβ₄ level is higher in exosomes from breast cancer patients with lung metastasis and increased exosomal ITGα_v in pancreatic cancer patients who developed liver metastasis than in those without metastasis. These results indicated that exosomal integrins isolated from circulating plasma may be used as organotropism biomarkers to predict organ-specific metastasis in cancer patients.The study by Lyden and colleagues⁹ expands our understanding of the organ-specific metastasis mechanisms and also highlights a crucial role of exosomes in promoting tumor metastasis. Indeed, another recent work in Nature Cell Biology shows that pancreatic cancer exosomes can increase liver metastatic burden by transferring macrophage migration inhibitory factor (MIF) to Kupffer cells and by recruiting immune cells to initiate pre-metastatic niche formation in the liver¹². Thus, strategies targeting these particular exosomal integrin molecules in this Nature paper⁹ may not be enough to prevent organ-specific metastasis. Besides, the limited integrin repertoire of bone-tropic exosomes identified by the proteome analysis calls for further investigation. This study also raises several intriguing questions: Do exosomal integrins have any effect on the recruitment of bone marrow-derived cells or immunosuppressive cells in priming pre-metastatic niche? What is the function of other exosome components such as RNA and DNA in determining organ-specific metastasis? Are these results universal to other type of cancer metastasis? Most importantly, how to translate this finding into clinical applications? Addressing these questions will help us unveil the mystery of organotropic metastasis.     

Exosomal long noncoding RNA HOXD-AS1 promotes prostate cancer metastasis via miR-361-5p/FOXM1 axis

Development of distant metastasis is the main cause of deaths in prostate cancer (PCa) patients. Understanding the mechanism of PCa metastasis is of utmost importance to improve its prognosis. The role of exosomal long noncoding RNA (lncRNA) has been reported not yet fully understood in the metastasis of PCa. Here, we discovered an exosomal lncRNA HOXD-AS1 is upregulated in castration resistant prostate cancer (CRPC) cell line derived exosomes and serum exosomes from metastatic PCa patients, which correlated with its tissue expression. Further investigation confirmed exosomal HOXD-AS1 promotes prostate cancer cell metastasis in vitro and in vivo by inducing metastasis associated phenotype. Mechanistically exosomal HOXD-AS1 was internalized directly by PCa cells, acting as competing endogenous RNA (ceRNA) to modulate the miR-361-5p/FOXM1 axis, therefore promoting PCa metastasis. In addition, we found that serum exosomal HOXD-AS1 was upregulated in metastatic PCa patients, especially those with high volume disease. And it is correlated closely with Gleason Score, distant and nodal metastasis, Prostatic specific antigen (PSA) recurrence free survival, and progression free survival (PFS). This sheds a new insight into the regulation of PCa distant metastasis by exosomal HOXD-AS1 mediated miR-361-5p/FOXM1 axis, and provided a promising liquid biopsy biomarker to guide the detection and treatment of metastatic PCa.Subject terms: Bone metastases, Prostate cancer     

Estrogen receptor beta promotes lung cancer invasion via increasing CXCR4 expression

Lung cancer is one of the most lethal malignant tumors in the world. The high recurrence and mortality rate make it urgent for scientists and clinicians to find new targets for better treatment of lung cancer. Early studies indicated that estrogen receptor β (ERβ) might impact the progression of non-small-cell lung cancer (NSCLC). However, the detailed mechanisms, especially its linkage to the CXCR4-mediated cell invasion, remain unclear. Here we found that ERβ could promote NSCLC cell invasion via increasing the circular RNA (circRNA), circ-TMX4, expression via directly binding to the 5′ promoter region of its host gene TMX4. ERβ-promoted circ-TMX4 could then sponge and inhibit the micro RNA (miRNA, miR), miR-622, expression, which can then result in increasing the CXCR4 messenger RNA translation via a reduced miRNA binding to its 3′ untranslated region (3′UTR). The preclinical study using an in vivo mouse model with orthotopic xenografts of NSCLC cells confirmed the in vitro data, and the human NSCLC database analysis and tissue staining also confirmed the linkage of ERβ/miR-622/CXCR4 signaling to the NSCLC progression. Together, our findings suggest that ERβ can promote NSCLC cell invasion via altering the ERβ/circ-TMX4/miR-622/CXCR4 signaling, and targeting this newly circ-TMX4/miR-622/CXCR4 signaling may help us find new treatment strategies to better suppress NSCLC progression.Subject terms: Non-small-cell lung cancer, Metastasis     

A Critical Role for the mTORC2 Pathway in Lung Fibrosis

A characteristic of dysregulated wound healing in IPF is fibroblastic-mediated damage to lung epithelial cells within fibroblastic foci. In these foci, TGF-β and other growth factors activate fibroblasts that secrete growth factors and matrix regulatory proteins, which activate a fibrotic cascade. Our studies and those of others have revealed that Akt is activated in IPF fibroblasts and it mediates the activation by TGF-β of pro-fibrotic pathways. Recent studies show that mTORC2, a component of the mTOR pathway, mediates the activation of Akt. In this study we set out to determine if blocking mTORC2 with MLN0128, an active site dual mTOR inhibitor, which blocks both mTORC1 and mTORC2, inhibits lung fibrosis. We examined the effect of MLN0128 on TGF-β-mediated induction of stromal proteins in IPF lung fibroblasts; also, we looked at its effect on TGF-β-mediated epithelial injury using a Transwell co-culture system. Additionally, we assessed MLN0128 in the murine bleomycin lung model. We found that TGF-β induces the Rictor component of mTORC2 in IPF lung fibroblasts, which led to Akt activation, and that MLN0128 exhibited potent anti-fibrotic activity in vitro and in vivo. Also, we observed that Rictor induction is Akt-mediated. MLN0128 displays multiple anti-fibrotic and lung epithelial-protective activities; it (1) inhibited the expression of pro-fibrotic matrix-regulatory proteins in TGF-β-stimulated IPF fibroblasts; (2) inhibited fibrosis in a murine bleomycin lung model; and (3) protected lung epithelial cells from injury caused by TGF-β-stimulated IPF fibroblasts. Our findings support a role for mTORC2 in the pathogenesis of lung fibrosis and for the potential of active site mTOR inhibitors in the treatment of IPF and other fibrotic lung diseases.     

ALK1 regulates the internalization of endoglin and the type III TGF-β receptor

Complex formation and endocytosis of transforming growth factor-β (TGF-β) receptors play important roles in signaling. However, their interdependence remained unexplored. Here, we demonstrate that ALK1, a TGF-β type I receptor prevalent in endothelial cells, forms stable complexes at the cell surface with endoglin and with type III TGF-β receptors (TβRIII). We show that ALK1 undergoes clathrin-mediated endocytosis (CME) faster than ALK5, type II TGF-β receptor (TβRII), endoglin, or TβRIII. These complexes regulate the endocytosis of the TGF-β receptors, with a major effect mediated by ALK1. Thus, ALK1 enhances the endocytosis of TβRIII and endoglin, while ALK5 and TβRII mildly enhance endoglin, but not TβRIII, internalization. Conversely, the slowly endocytosed endoglin has no effect on the endocytosis of either ALK1, ALK5, or TβRII, while TβRIII has a differential effect, slowing the internalization of ALK5 and TβRII, but not ALK1. Such effects may be relevant to signaling, as BMP9-mediated Smad1/5/8 phosphorylation is inhibited by CME blockade in endothelial cells. We propose a model that links TGF-β receptor oligomerization and endocytosis, based on which endocytosis signals are exposed/functional in specific receptor complexes. This has broad implications for signaling, implying that complex formation among various receptors regulates their surface levels and signaling intensities.     

Gamma synuclein promotes cancer metastasis through the MKK3/6-p38MAPK cascade

Gamma synuclein (SNCG) is a neuronal protein that is also aberrantly overexpressed in various types of human cancer. SNCG overexpression promotes cancer invasion and metastasis. However, the mechanisms that drive cancer metastasis upon SNCG expression remain elusive. Elucidation of the mechanisms underlying the promotion of cancer metastasis by SNCG may help discover therapeutic avenues for SNCG-overexpressed cancer. Here, we show that SNCG promotes transforming growth factor-β (TGF-β)-induced p38 mitogen-activated protein kinase (MAPK) phosphorylation. Mechanistically, SNCG promotes p38MAPK phosphorylation by interacting with the MAPK kinase 3/6 (MKK3/6) and prevents their degradation. SNCG knockdown leads to a decrease in TGF-β-induced phosphorylation of MKK3/6; and abrogates the induction of matrix metalloproteinase (MMP)-9 expression by TGF-β and its target gene Twist1. Furthermore, p38MAPK inhibition abrogates the promotion of MMP-9 expression and cancer cell invasion by SNCG. Both p38MAPK and MMP inhibitors can suppress the promotion of cancer cell invasion by SNCG. Finally, overexpression of SNCG in liver cancer cells promotes lung metastasis, which can be suppressed by the p38MAPK inhibitor. Together, our data uncover a previously unknown role of SNCG in promoting TGF-β-MKK3/6-p38MAPK signaling. This study highlights the critical role of p38MAPK in the promotion of cancer metastasis by SNCG, and indicates that p38MAPK inhibitor may serve as a potential therapeutic for SNCG-overexpressed cancer.     

Honokiol Inhibits Non-Small Cell Lung Cancer Cell Migration by Targeting PGE2-Mediated Activation of β-Catenin Signaling

Lung cancer remains a leading cause of death due to its metastasis to distant organs. We have examined the effect of honokiol, a bioactive constituent from the Magnolia plant, on human non-small cell lung cancer (NSCLC) cell migration and the molecular mechanisms underlying this effect. Using an in vitro cell migration assay, we found that treatment of A549, H1299, H460 and H226 NSCLC cells with honokiol resulted in inhibition of migration of these cells in a dose-dependent manner, which was associated with a reduction in the levels of cyclooxygenase-2 (COX-2) and prostaglandin E₂ (PGE₂). Celecoxib, a COX-2 inhibitor, also inhibited cell migration. Honokiol inhibited PGE₂-enhanced migration of NSCLC cells, inhibited the activation of NF-κB/p65, an upstream regulator of COX-2, in A549 and H1299 cells, and treatment of cells with caffeic acid phenethyl ester, an inhibitor of NF-κB, also inhibited migration of NSCLC cells. PGE₂ has been shown to activate β-catenin signaling, which contributes to cancer cell migration. Therefore, we checked the effect of honokiol on β-catenin signaling. It was observed that treatment of NSCLC cells with honokiol degraded cytosolic β-catenin, reduced nuclear accumulation of β-catenin and down-regulated matrix metalloproteinase (MMP)-2 and MMP-9, which are the down-stream targets of β-catenin and play a crucial role in cancer cell metastasis. Honokiol enhanced: (i) the levels of casein kinase-1α, glycogen synthase kinase-3β, and (ii) phosphorylation of β-catenin on critical residues Ser⁴⁵, Ser^33/37 and Thr⁴¹. These events play important roles in degradation or inactivation of β-catenin. Treatment of celecoxib also reduced nuclear accumulation of β-catenin in NSCLC cells. FH535, an inhibitor of Wnt/β-catenin pathway, inhibited PGE₂-enhanced cell migration of A549 and H1299 cells. These results indicate that honokiol inhibits non-small cell lung cancer cells migration by targeting PGE₂-mediated activation of β-catenin signaling.     

Suberoylanilide hydroxamic acid (SAHA) inhibits transforming growth factor-beta 2-induced increases in aqueous humor outflow resistance

Transforming growth factor-beta 2 (TGF-β2) is highly concentrated in the aqueous humor of primary open-angle glaucoma patients. TGF-β2 causes fibrosis of outflow tissues, such as the trabecular meshwork (TM), and increases intraocular pressure by increasing resistance to aqueous humor outflow. Recently, histone deacetylase (HDAC) activity was investigated in fibrosis in various tissues, revealing that HDAC inhibitors suppress tissue fibrosis. However, the effect of HDAC inhibitors on fibrosis in the eye was not determined. Here, we investigated the effect of suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor, on TGF-β2-induced increased resistance to aqueous humor outflow. We found that SAHA suppressed TGF-β2-induced outflow resistance in perfused porcine eyes. Moreover, SAHA cotreatment suppressed TGF-β2-induced ocular hypertension in rabbits. The permeability of monkey TM (MTM) and Schlemm’s canal (MSC) cell monolayers was decreased by TGF-β2 treatment. SAHA inhibited the effects of TGF-β2 on the permeability of these cells. TGF-β2 also increased the expression of extracellular matrix proteins (fibronectin and collagen type I or IV) in MTM, MSC, and human TM (HTM) cells, while SAHA inhibited TGF-β2-induced extracellular matrix protein expression in these cells. SAHA also inhibited TGF-β2-induced phosphorylation of Akt and ERK, but did not inhibit Smad2/3 phosphorylation, the canonical pathway of TGF-β signaling. Moreover, SAHA induced the expression of phosphatase and tensin homolog, a PI3K/Akt signaling factor, as well as bone morphogenetic protein 7, an endogenous antagonist of TGF-β. These results imply that SAHA prevents TGF-β2-induced increases in outflow resistance and regulates the non-Smad pathway of TGF-β signaling in TM and MSC cells.     

Tight junction protein 1 is regulated by transforming growth factor-β and contributes to cell motility in NSCLC cells

Tight junction protein 1 (TJP1), a component of tight junction, has been reported to play a role in protein networks as an adaptor protein, and TJP1 expression is altered during tumor development. Here, we found that TJP1 expression was increased at the RNA and protein levels in TGF-β-stimulated lung cancer cells, A549. SB431542, a type-I TGF-β receptor inhibitor, as well as SB203580, a p38 kinase inhibitor, significantly abrogated the effect of TGF-β on TJP1 expression. Diphenyleneiodonium, an NADPH oxidase inhibitor, also attenuated TJP1 expression in response to TGF-β in lung cancer cells. When TJP1 expression was reduced by shRNA lentiviral particles in A549 cells (A549-sh TJP1), wound healing was much lower than in cells infected with control viral particles. Taken together, these data suggest that TGF-β enhances TJP1 expression, which may play a role beyond structural support in tight junctions during cancer development. [BMB Reports 2015; 48(2): 115-120]     

Endothelial-Mesenchymal Transition of Brain Endothelial Cells: Possible Role during Metastatic Extravasation

Cancer progression towards metastasis follows a defined sequence of events described as the metastatic cascade. For extravasation and transendothelial migration metastatic cells interact first with endothelial cells. Yet the role of endothelial cells during the process of metastasis formation and extravasation is still unclear, and the interaction between metastatic and endothelial cells during transendothelial migration is poorly understood. Since tumor cells are well known to express TGF-β, and the compact endothelial layer undergoes a series of changes during metastatic extravasation (cell contact disruption, cytoskeletal reorganization, enhanced contractility), we hypothesized that an EndMT may be necessary for metastatic extravasation. We demonstrate that primary cultured rat brain endothelial cells (BEC) undergo EndMT upon TGF-β1 treatment, characterized by the loss of tight and adherens junction proteins, expression of fibronectin, β1-integrin, calponin and α-smooth muscle actin (SMA). B16/F10 cell line conditioned and activated medium (ACM) had similar effects: claudin-5 down-regulation, fibronectin and SMA expression. Inhibition of TGF-β signaling during B16/F10 ACM stimulation using SB-431542 maintained claudin-5 levels and mitigated fibronectin and SMA expression. B16/F10 ACM stimulation of BECs led to phosphorylation of Smad2 and Smad3. SB-431542 prevented SMA up-regulation upon stimulation of BECs with A2058, MCF-7 and MDA-MB231 ACM as well. Moreover, B16/F10 ACM caused a reduction in transendothelial electrical resistance, enhanced the number of melanoma cells adhering to and transmigrating through the endothelial layer, in a TGF-β-dependent manner. These effects were not confined to BECs: HUVECs showed TGF-β-dependent SMA expression when stimulated with breast cancer cell line ACM. Our results indicate that an EndMT may be necessary for metastatic transendothelial migration, and this transition may be one of the potential mechanisms occurring during the complex phenomenon known as metastatic extravasation.