BackgroundTGF-β promotes tumor invasion and metastasis through inducing epithelial-mesenchymal transition (EMT) in non-small cell lung cancer (NSCLC). Circular RNAs (circRNAs) are recognized as functional non-coding RNAs involved in human cancers. However, whether and how circRNAs contribute to TGF-β-induced EMT and metastasis in NSCLC remain vague. Here, we investigated the regulation and function of Circular RNA hsa_circ_0008305 (circPTK2) in TGF-β-induced EMT and tumor metastasis, as well as a link between circPTK2 and transcriptional intermediary factor 1 γ (TIF1γ) in NSCLC.MethodsCircular RNAs were determined by human circRNA Array analysis, real-time quantitative reverse transcriptase PCR and northern blot. Luciferase reporter, RNA-binding protein immunoprecipitation (RIP), RNA pull-down and fluorescence in situ hybridization (FISH) assays were employed to test the interaction between circPTK2 and miR-429/miR-200b-3p. Ectopic overexpression and siRNA-mediated knockdown of circPTK2, TGF-β-induced EMT, Transwell migration and invasion in vitro, and in vivo experiment of metastasis were used to evaluate the function of circPTK2. Transcription and prognosis analyses were done in public databases.ResultsCircPTK2 and TIF1γ were significantly down-regulated in NSCLC cells undergoing EMT induced by TGF-β. CircPTK2 overexpression augmented TIF1γ expression, inhibited TGF-β-induced EMT and NSCLC cell invasion, whereas circPTK2 knockdown had the opposite effects. CircPTK2 functions as a sponge of miR-429/miR-200b-3p, and miR-429/miR-200b-3p promote TGF-β-induced EMT and NSCLC cell invasion by targeting TIF1γ. CircPTK2 overexpression inhibited the invasion-promoting phenotype of endogenous miR-429/miR-200b-3p in NSCLC cells in response to TGF-β. CircPTK2 overexpression significantly decreased the expression of Snail, an important downstream transcriptional activator of TGF-β/Smad signaling. In an in vivo experiment of metastasis, circPTK2 overexpression suppressed NSCLC cell metastasis. Moreover, circPTK2 expression was dramatically down-regulated and positively correlated with TIF1γ expression in human NSCLC tissues. Especially, circPTK2 was significantly lower in metastatic NSCLC tissues than non-metastatic counterparts.ConclusionOur findings show that circPTK2 (hsa_circ_0008305) inhibits TGF-β-induced EMT and metastasis by controlling TIF1γ in NSCLC, revealing a novel mechanism by which circRNA regulates TGF-β-induced EMT and tumor metastasis, and suggesting that circPTK2 overexpression could provide a therapeutic strategy for advanced NSCLC.Electronic supplementary materialThe online version of this article (10.1186/s12943-018-0889-7) contains supplementary material, which is available to authorized users.

No abstract

No abstract

Quaking (QKI) proteins belong to the signal transduction and activation of RNA (STAR) family of RNA-binding proteins that have multiple functions in RNA biology. Here, we show that QKI-5 is dramatically decreased in metastatic lung adenocarcinoma (LUAD). QKI-5 overexpression inhibits TGF-b-induced epithelialmesenchymal transition (EMT) and invasion, whereas QKI-5 knockdown has the opposite effect. QKI-5 overexpression and silencing suppresses and promotes TGF-b-stimulated metastasis in vivo, respectively. QKI-5 inhibits TGF-b-induced EMT and invasion in a TGFbR1-dependent manner. KLF6 knockdown increases TGFbR1 expression and promotes TGF-b-induced EMT, which is partly abrogated by QKI-5 overexpression. Mechanistically, QKI-5 directly interacts with the TGFbR1 3 0 UTR and causes post-transcriptional degradation of TGFbR1 mRNA, thereby inhibiting TGF-b-induced SMAD3 phosphorylation and TGF-b/SMAD signaling. QKI-5 is positively regulated by KLF6 at the transcriptional level. In LUAD tissues, KLF6 is lowly expressed and positively correlated with QKI-5 expression, while TGFbR1 expression is up-regulated and inversely correlated with QKI-5 expression. We reveal a novel mechanism by which KLF6 transcriptionally regulates QKI-5 and suggest that targeting the KLF6/QKI-5/TGFbR1 axis is a promising targeting strategy for metastatic LUAD.

AlkB homolog 5 (ALKBH5) has been revealed as a key RNA N6‐methyladenosine (m6A) demethylase that is implicated in development and diseases. However, the function of ALKBH5 in TGF‐β‐induced epithelial‐mesenchymal transition (EMT) and tumor metastasis of non‐small‐cell lung cancer (NSCLC) remains unknown. Here, we firstly show that ALKBH5 expression is significantly reduced in metastatic NSCLC. ALKBH5 overexpression inhibits TGF‐β‐induced EMT and invasion of NSCLC cells, whereas ALKBH5 knockdown promotes the corresponding phenotypes. ALKBH5 overexpression suppresses TGF‐β‐stimulated NSCLC cell metastasis in vivo. ALKBH5 overexpression decreases the expression and mRNA stability of TGFβR2 and SMAD3 but increases those of SMAD6, while ALKBH5 knockdown causes the opposite results. Importantly, ALKBH5 overexpression or knockdown leads respectively to an attenuated or augmented phosphorylation of SMAD3, an indispensable downstream effector that activates TGF‐β/SMAD signaling. Moreover, m6A‐binding proteins YTHDF1/3 promotes TGFβR2 and SMAD3 expression, and YTHDF2 inhibits SMAD6 expression. YTHDF1/2/3 facilitates TGF‐β‐stimulated EMT and invasion of NSCLC cells. Mechanistically, ALKBH5 affects TGFβR2, SMAD3 and SMAD6 expression and mRNA stability by erasing m6A modification in NSCLC cells. ALKBH5 weakens YTHDF1/3‐mediated TGFβR2 and SMAD3 mRNA stabilization, and abolishes YTHDF2‐mediated SMAD6 mRNA degradation, supporting the notion that ALKBH5 inhibits TGF‐β‐induced EMT and invasion of NSCLC cells via YTHD1/2/3‐mediated mechanism. Taken together, our findings highlight an important role of ALKBH5 in regulating TGF‐β/SMAD signaling, and establish a mechanistic interaction of ALKBH5 with TGFβR2/SMAD3/SMAD6 for controlling TGF‐β‐induced EMT in NSCLCs.