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.

No abstract

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.

Regulator of G-protein signaling 6 (RGS6) is a newly discovered tumor suppressor that has been shown to be protective in development of various cancers such as breast cancer and bladder cancer. But the mechanisms underlying these tumor-suppressing functions of RGS6 are not fully understood. Here, we discover a novel function of RGS6 in suppressing TGF-β-induced epithelial–mesenchymal transition (EMT) of non-small cell lung cancer (NSCLC) cells and in vivo NSCLC metastasis. Using both bioinformatics and experimental tools, we showed that RGS6 was downregulated in lung cancer tissues compared to noncancerous counterparts, and low expression of RGS6 was associated with poor survival of lung cancer patients. Overexpression of RGS6 suppressed TGF-β-induced EMT in vitro and TGF-β-promoted metastasis in vivo, by impairing gene expression of downstream effectors induced by the canonical TGF-β-SMAD signaling. The ability of RGS6 to suppress TGF-β-SMAD-mediated gene expression relied on its binding to SMAD4 to prevent complex formation between SMAD4 and SMAD2/3, but independent of its regulation of the G-protein signaling. Interaction between RGS6 and SMAD4 caused less nuclear entry of p-SMAD3 and SMAD4, resulting in inefficient SMAD3-mediated gene expression. Taken together, our findings reveal a novel and noncanonical role of RGS6 in regulation of TGF-β-induced EMT and metastasis of NSCLC and identify RGS6 as a prognostic marker and a potential novel target for NSCLC therapy.