izhen Hu

Curcumin inhibits lung cancer cell migration and invasion through Rac1-dependent signaling pathway

Curcumin, a natural and crystalline compound isolated from the plant Curcuma longa with low toxicity in normal cells, has been shown to protect against carcinogenesis and prevent tumor development. However, little is known about antimetastasis effects and mechanism of curcumin in lung cancer. Rac1 is an important small Rho GTPases family protein and has been widely implicated in cytoskeleton rearrangements and cancer cell migration, invasion and metastasis. In this study, we examined the influence of curcumin on in vitro invasiveness of human lung cancer cells and the expressions of Rac1. The results indicate that curcumin at 10 μM slightly reduced the proliferation of 801D lung cancer cells but showed an obvious inhibitory effect on epidermal growth factor or transforming growth factor β1-induced lung cancer cell migration and invasion. Meanwhile, we demonstrated that the suppression of invasiveness correlated with inhibition of Rac1/PAK1 signaling pathways and matrix metalloproteinase (MMP) 2 and 9 protein expression by combining curcumin treatment with the methods of Rac1 gene silence and overexpression in lung cancer cells. Laser confocal microscope also showed that Rac1-regulated actin cytoskeleton rearrangement may be involved in anti-invasion effect of curcumin on lung cancer cell. At last, through xenograft experiments, we confirmed the connection between Rac1 and the growth and metastasis inhibitory effect of curcumin in vivo. In summary, these data demonstrated that low-toxic levels of curcumin could efficiently inhibit migration and invasion of lung cancer cells through inhibition of Rac1/PAK1 signaling pathway and MMP-2 and MMP-9 expression, which provided a novel insight into the molecular mechanism of curcumin against lung cancer.

MiR-206 inhibits HGF-induced epithelial-mesenchymal transition and angiogenesis in non-small cell lung cancer via c-Met /PI3k/ Akt/mTOR pathway

MiR-206 is low expression in lung cancers and associated with cancer metastasis. However, the roles of miR-206 in epithelial-mesenchymal transition (EMT) and angiogenesis in lung cancer remain unknown. In this study, we find that hepatocyte growth factor (HGF) induces EMT, invasion and migration in A549 and 95D lung cancer cells, and these processes could be markedly inhibited by miR-206 overexpression. Moreover, we demonstrate that miR-206 directly targets c-Met and inhibits its downstream PI3k/Akt/mTOR signaling pathway. In contrast, miR-206 inhibitors promote the expression of c-Met and activate the PI3k/Akt/mTOR signaling, and this effect could be attenuated by the PI3K inhibitor. Moreover, c-Met overexpression assay further confirms the significant inhibitory effect of miR-206 on HGF-induced EMT, cell migration and invasion. Notably, we also find that miR-206 effectively inhibits HGF-induced tube formation and migration of human umbilical vein endothelial cells (HUVECs), and the mechanism is also related to inhibition of PI3k/Akt/mTOR signaling. Finally, we reveal the inhibitory effect of miR-206 on EMT and angiogenesis in xenograft tumor mice model. Taken together, miR-206 inhibits HGF-induced EMT and angiogenesis in lung cancer by suppressing c-Met/PI3k/Akt/mTOR signaling. Therefore, miR-206 might be a potential target for the therapeutic strategy against EMT and angiogenesis of lung cancer.

Silencing of Rac1 modifies lung cancer cell migration, invasion and actin cytoskeleton rearrangements and enhances chemosensitivity to antitumor drugs

Rac1, an intracellular signal transducer, regulates a variety of cell functions, including the organization of the cytoskeleton, cell migration, and invasion. Overexpression of Rac1 has been reported in several human cancers. However, the underlying mechanisms are not well understood. In the present study, we evaluated the possibility of Rac1 as an appropriate molecular target for cancer gene therapy. The expression of Rac1 in 150 primary non-small cell lung cancer tissues (NSCLC) and 30 normal paraneoplastic lung tissues was determined by immunohistochemical staining, and the correlation of Rac1 overexpression with clinicopathological factors was evaluated. Overexpression of Rac1 was detected in 94 of 150 lung cancer specimens, the incidence rate being higher than that in normal lung tissue specimens. In addition, overexpression of Rac1 was also associated with poor differentiation, high TNM stage, and lymph node metastasis in NSCLC patients. Moreover, RNAi-mediated suppression of Rac1 expression reduced lamellipodia formation, migration and invasion potential of a lung cancer cell carcinoma cell line, 801D. Down-regulation of Rac1 expression also reduced the expression of Pak1. NSC23766, an inhibitor of Rac1 activity, could also inhibit lung cancer cell migration, invasion and induce rearrangements of the actin cytoskeleton. Furthermore, the suppression of Rac1 expression also sensitized cells to antitumor drugs. These results indicate that the overexpression of Rac1 is tightly associated with an aggressive phenotype of lung cancer cells. Therefore, we proposed that Rac1 could be a potential molecular target of gene therapy by RNAi-targeting in lung cancer cells.

Lysosomal membrane permeabilization is involved in curcumin-induced apoptosis of A549 lung carcinoma cells

We previously reported that curcumin inhibited lung cancer A549 cells growth and promoted cell apoptosis in vitro. In this study, we further examined the apoptosis-related parameters, including lysosomal damage and cathepsin activation, in A549 cells exposed to curcumin. We found that curcumin caused lysosomal membrane permeabilization (LMP) and cytosolic relocation of cathepsin B (cath B) and cathepsin D (cath D). However, only Z-FA-fmk (a cath B inhibitor) but not pepstatin A (a cath D inhibitor) inhibited curcumin-induced cell apoptosis, mitochondrial membrane potential loss, and cytochrome c release. The antioxidant N-acetylcysteine and glutathione attenuated LMP, suggesting that lysosomal destabilization was dependent on the elevation of reactive oxygen species and which precedes mitochondrial dysfunction. These findings indicated a novel pathway for curcumin regulation of ROS-lysosomal–mitochondrial pathway and provided the key mechanism of regulation of LMP in cell apoptosis, which may be exploited for cancer treatment.

miR-206 regulates cisplatin resistance and EMT in human lung adenocarcinoma cells partly by targeting MET

MicroRNAs (miRNAs) play a critical role in drug resistance and epithelial-mesenchymal transition (EMT). The aims of this study were to explore the potential role of miR-206 in governing cisplatin resistance and EMT in lung cancer cells. We found that both lung adenocarcinoma A549 cisplatin-resistant cells (A549/DDP) and H1299 cisplatin-resistant cells (H1299/DDP) acquired mesenchymal features and were along with low expression of miR-206 and high migration and invasion abilities. Ectopic expression of miR-206 mimics inhibited cisplatin resistance, reversed the EMT phenotype, decreased the migration and invasion in these DDP-resistant cells. In contrast, miR-206 inhibitors increased cisplatin resistance, EMT, cell migration and invasion in non-DDP-resistant cells. Furthermore, we found that MET is the direct target of miR-206 in lung cancer cells. Knockdown of MET exhibited an EMT and DDP resistant inhibitory effect on DDP-resistant cells. Conversely, overexpression of MET in non-DDP- resistant cells produced a promoting effect on cell EMT and DDP resistance. In lung adenocarcinoma tissues, we demonstrated that low expression of miR-206 were also correlated with increased cisplatin resistance and MET expression. In addition, we revealed that miR-206 overexpression reduced cisplatin resistance and EMT in DDP-resistant cells, partly due to inactivation of MET/PI3K/AKT/mTOR signaling pathway, and subsequent downregulation of MDR1, ZEB1 and Snail expression. Finally, we found that miR-206 could also sensitize A549/DDP cells to cisplatin in mice model. Taken together, our study implied that activation of miR-206 or inactivation of its target gene pathway could serve as a novel approach to reverse cisplatin resistance in lung adenocarcinomas cells.

Downregulation of LIMK1 level inhibits migration of lung cancer cells and enhances sensitivity to chemotherapy drugs.

LIM kinase 1 (LIMK1) is a member of a novel class of serine-threonine protein kinases, which plays an important role in malignant transformation. High expression of LIM kinase 1 (LIMK1) has been detected in various invasive cancers. Here, we showed that LIMK1 was overexpressed in non-small cell lung cancer tissues (NSCLC) and cell lines. Expression of LIMK1 was detected in 115 of 150 lung cancer tissues, the frequency being more significant than in lung tissues. In addition, overexpression of LIMK1 was also associated with high TNM stage and lymph node metastasis in NSCLC patients. Moreover, RNAi-mediated suppression of LIMK1 expression markedly inhibited migration and invasion of 801D lung cancer cells. Furthermore, silencing of LIMK1 sensitized 801D cells to chemotherapeutic drugs of cisplatin and gemcitabine. These results indicate that the overexpression of LIMK1 is tightly associated with an aggressive phenotype of lung cancer cells, knockdown of LIMK1 suppressed cell migration and invasion, enhanced chemosensitivity, suggesting a potential therapeutic target for lung cancer.

Exploration of inhibitory mechanisms of curcumin in lung cancer metastasis using a miRNA- transcription factor-target gene network

The present study was aimed to unravel the inhibitory mechanisms of curcumin for lung cancer metastasis via constructing a miRNA-transcription factor (TF)-target gene network. Differentially expressed miRNAs between human high-metastatic non-small cell lung cancer 95D cells treated with and without curcumin were identified using a TaqMan human miRNA array followed by real-time PCR, out of which, the top 6 miRNAs (miR-302b-3p, miR-335-5p, miR-338-3p, miR-34c-5p, miR-29c-3p and miR-34a-35p) with more verified target genes and TFs than other miRNAs as confirmed by a literature review were selected for further analysis. The miRecords database was utilized to predict the target genes of these 6 miRNAs, TFs of which were identified based on the TRANSFAC database. The findings of the above procedure were used to construct a miRNA-TF-target gene network, among which miR-34a-5p, miR-34c-5p and miR-302b-3p seemed to regulate CCND1, WNT1 and MYC to be involved in Wnt signaling pathway through the LEF1 transcription factor. Therefore, we suggest miR-34a-5p/miR-34c-5p/miR-302b-3p —LEF1—CCND1/WNT1/MYC axis may be a crucial mechanism in inhibition of lung cancer metastasis by curcumin.

Identification of carcinogenic potential-associated molecular mechanisms in CD133+ A549 cells based on microRNA profiles

This study aimed to identify carcinogenic potential-related molecular mechanisms in cancer stem cells (CSCs) in lung cancer. CD133+ and CD133− subpopulations were sorted from A549 cells using magnetic-activated cell sorting. The abilities to form sphere and clone, proliferate, migrate, and invade were compared between CD133+ and CD133− cells, as well as drug sensitivity. Thereafter, microRNA (miRNA) profiles were performed to identify differentially expressed miRNAs between CD133+ and CD133− subpopulation. Following, bioinformatic methods were used to predict target genes for differentially expressed miRNAs and perform enrichment analysis. Furthermore, the mammalian target of rapamycin (mTOR) signaling pathways and CSC property-associated signaling pathways were explored and visualized in regulatory network among competitive endogenous RNA (ceRNA), miRNA, and target gene. CD133+ subpopulation showed greater oncogenic potential than CD133− subpopulation. In all, 14 differentially expressed miRNAs were obtained and enriched in 119 pathways, including five upregulated (hsa-miR-23b-3p, -23a-3p, -15b-5p, -24-3p, and -4734) and nine downregulated (hsa-miR-1246, -30b-5p, -5096, -6510-5p, has-miR-7110-5p, -7641, -3197, -7108-5p, and -6791-5p). For mTOR signaling pathway, eight differential miRNAs (hsa-miR-23b-3p, -23a-3p, -15b-5p, -24-3p, -4734, -1246, -7641, and -3197) and 39 target genes (e.g., AKT1, AKT2, PIK3CB, PIK3CG, PIK3R1, PIK3CA, and PIK3CD) were involved, as well as some ceRNAs. Besides, for CSC property-related signaling pathways, six miRNAs (hsa-miR-1246, -15b-5p, -30b-5p, -3197, -4734, and -7110-5p) were dramatically enriched in Hedgehog, Notch, and Wnt signaling pathways via regulating 108 target genes (e.g., DVL1, DVL3, WNT3A, and WNT5A). The mTOR and CSC property-associated signaling pathways may be important oncogenic molecular mechanisms in CD133+ A549 cells.

Identification of lymph node metastasis-related microRNAs in lung adenocarcinoma and analysis of the underlying mechanisms using a bioinformatics approach

This study aimed to screen lymphatic metastasis-related microRNAs (miRNAs) in lung adenocarcinoma and explore their underlying mechanisms using bioinformatics. The miRNA expression in primary lung adenocarcinoma, matched adjacent non-tumorigenic and lymph node metastasis tissues of patients were profiled via microarray. The screened metastasis-related miRNAs were then validated using quantitative real-time PCR in a second cohort of lung adenocarcinoma patients with lymphatic metastasis. Significance was determined using a paired t-test. Target genes of the metastasis-related miRNAs were predicted using TargetScan, and transcription factors (TFs) were predicted based on the TRANSFAC and ENCODE databases. Furthermore, the related long non-coding RNAs (lncRNAs) were screened with starBase v2.0. The miRNA-TF-mRNA and lncRNA-miRNA-mRNA networks were constructed to determine the key interactions associated with lung adenocarcinoma metastasis. According to the miRNA microarray results, there were 10 miRNAs that were differentially expressed in metastatic tissues compared with primary tumor and adjacent non-tumorigenic tissues. Among them were increased levels of miR-146a-5p, miR-342-3p, and miR-150-5p, which were validated in the second cohort. Based on the miRNA-TF-mRNA network, vascular endothelial growth factor A and transcription factors (TFs) including TP53, SMAD4, and EP300 were recognized as critical targets of the three miRNAs. Interactions involving SNHG16–miR-146a-5p–SMAD4 and RP6-24A23.7–miR-342-3p/miR-150-5p–EP300 were highlighted according to the lncRNA-miRNA-mRNA network. miR-146a-5p, miR-342-3p, and miR-150-5p are lymphatic metastasis-related miRNAs in lung adenocarcinoma. Bioinformatics analyses demonstrated that SNHG16 might inhibit the interaction between miR-146a-5p and SMAD4, while RP6-24A23.7 might weaken miR-342-3p–EP300 and miR-150-5p–EP300 interactions in metastasis.