PLK1/vimentin signaling facilitates immune escape by recruiting Smad2/3 to PD-L1 promoter in metastatic lung adenocarcinoma.

The prerequisite function of vimentin for the epithelial-mesenchymal transition (EMT) is not clearly elucidated yet. Here, we show that vimentin phosphorylated by PLK1, triggers TGF-ß-signaling, which consequently leads to metastasis and PD-L1 expression for immune suppression in lung adenocarcinoma. The clinical correlation between expression of both vimentin and PLK1, and overall survival rates of patients was significant in lung adenocarcinoma but not in squamous cell carcinoma. The phosphorylation of vimentin was accompanied by the activation of PLK1 during TGF-ß-induced EMT in lung adenocarcinoma. Among the several phosphorylation sites determined by phospho-proteomic analysis and the site-specific mutagenesis, the phosphorylation at S339 displayed the most effective metastasis and tumourigenesis with the highest expression of PD-L1, compared with that of wild-type and other versions in both 3D cell culture and tail-vein injection metastasis models. Phosphomimetic vimentin at S339 interacted with p-Smad2 for its nuclear localization, leading to the expression of PD-L1. Clinical relevance revealed the inverse correlation between the survival rates of patients and the expressions of VIM, PLK1, and CD274 in primary and metastatic lung adenocarcinoma. Thus, PLK1-mediated phosphorylation of vimentin activates TGF-ß signaling pathway, leading to the metastasis and immune escape through the expression of PD-L1, functioning as a shuttling protein in lung adenocarcinoma.

Combination of Inhibitors of USP7 and PLK1 has a Strong Synergism against Paclitaxel Resistance.

USP7 is a promising target for the development of cancer treatments because of its high expression and the critical functions of its substrates in carcinogenesis of several different carcinomas. Here, we demonstrated the effectiveness of targeting USP7 in advanced malignant cells showing high levels of USP7, especially in taxane-resistant cancer. USP7 knockdown effectively induced cell death in several cancer cells of lung, prostate, and cervix. Depletion of USP7 induced multiple spindle pole formation in mitosis, and, consequently, resulted in mitotic catastrophe. When USP7 was blocked in the paclitaxel-resistant lung cancer NCI-H460TXR cells, which has resistance to mitotic catastrophe, NCI-H460TXR cells underwent apoptosis effectively. Furthermore, combination treatment with the mitotic kinase PLK1 inhibitor volasertib and the USP7 inhibitor P22077 showed a strong synergism through down-regulation of MDR1/ABCB1 in paclitaxel-resistant lung cancer. Therefore, we suggest USP7 is a promising target for cancer therapy, and combination therapy with inhibitors of PLK1 and USP7 may be valuable for treating paclitaxel-resistant cancers, because of their strong synergism.

Methylation of the CDX2 promoter in Helicobacter pylori-infected gastric mucosa increases with age and its rapid demethylation in gastric tumors is associated with upregulated gene expression.

Pathological changes in the epigenetic landscape of chromatin are hallmarks of cancer. The caudal-type homeobox gene CDX2 is not expressed in normal gastric epithelia but rather in adult intestinal epithelia, and it is overexpressed in intestinal metaplasia (IM). However, it remains unclear how CDX2 transcription is suppressed in normal gastric epithelial cells and overexpressed in IM. Here, we demonstrate that methylation of the CDX2 promoter increases with age in Helicobacter pylori-positive, noncancerous gastric tissue, whereas the promoter is demethylated in paired gastric tumors in which CDX2 is upregulated. Moreover, we also found that the CDX2 promoter is demethylated in IM as well as gastric tumor. Immunohistochemistry revealed that CDX2 is present in foci of parts of the gastric mucosae but highly expressed in IM as well as in gastric tumors, suggesting that the elevated level of CDX2 in IM and gastric tumors may be attributable to promoter demethylation. Our data suggest that CDX2 repression may be associated with promoter methylation in noncancerous H. pylori-positive mucosa but its upregulation might be attributable to increased promoter activity mediated by chromatin remodeling during gastric carcinogenesis.

Active PLK1-driven metastasis is amplified by TGF-ß signaling that forms a positive feedback loop in non-small cell lung cancer.

Early findings that PLK1 is highly expressed in cancer have driven an exploration of its functions in metastasis. However, whether PLK1 induces metastasis in vivo and its underlying mechanisms in NSCLC have not yet been determined. Here, we show that the expression of active PLK1 phosphorylated at T210, abundant in TGF-ß-treated lung cells, potently induced metastasis in a tail-vein injection model. Active PLK1 with intact polo-box and ATP-binding domains accelerated cell motility and invasiveness by triggering EMT reprogramming, whereas a phosphomimetic version of p-S137-PLK1 did not, indicating that the phosphorylation status of PLK1 may determine the cell traits. Active PLK1-driven invasiveness upregulated TGF-ß signaling and TSG6 encoded by TNFAIP6. Loss of TNFAIP6 disturbed the metastatic activity induced by active PLK1 or TGF-ß. Clinical relevance shows that PLK1 and TNFAIP6 are strong predictors of poor survival rates in metastatic NSCLC patients. Therefore, we suggest that active PLK1 promotes metastasis by upregulating TGF-ß signaling, which amplifies its metastatic properties by forming a positive feedback loop and that the PLK1/TGF-ß-driven metastasis is effectively blocked by targeting PLK1 and TSG6, providing PLK1 and TSG6 as negative markers for prognostics and therapeutic targets in metastatic NSCLC.

Correction: Active PLK1-driven metastasis is amplified by TGF-ß signaling that forms a positive feedback loop in non-small cell lung cancer.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

7-O-Methylwogonin from Scutellaria baicalensis Disturbs Mitotic Progression by Inhibiting Plk1 Activity in Hep3B Cells.

Polo-like kinase 1, a mitotic Ser/Thr kinase, has emerged as a molecular target for the development of anticancer drugs. In this study, we found that polo-like kinase 1 activity was inhibited by 7-O-methylwogonin and related flavones, including baicalein, dihydrobaicalein, and viscidulin II, isolated from Scutellaria baicalensis. Although dihydrobaicalein exhibited the highest polo-like kinase 1 inhibitory activity among the four compounds, it also inhibited other kinases, such as vaccinia-related kinase 2 and polo-like kinase 2. Baicalein and viscidulin II also showed low selectivity to polo-like kinase 1 since they inhibited polo-like kinase 3 and polo-like kinase 2, respectively. However, 7-O-methylwogonin exhibited selective polo-like kinase 1 inhibitory activity, as evidenced from in vitro kinase assays based on fluorescence resonance energy transfer assays and ADP-Glo kinase assays. In addition, examination of mitotic morphology and immunostaining using specific antibodies for the mitotic markers, p-histone H3 and mitotic protein monoclonal 2, in Hep3B cells showed that 7-O-methylwogonin treatment increased mitotic cell populations due to inhibition of mitotic progression as a result of polo-like kinase 1 inhibition. The pattern of 7-O-methylwogonin-induced mitotic arrest was similar to that of BI 2536, a specific polo-like kinase 1 inhibitor. Thus, it was suggested that 7-O-methylwogonin disturbed mitotic progression by inhibiting polo-like kinase 1 activity. These data suggest that 7-O-methylwogonin, a polo-like kinase 1 inhibitor, may be a useful anticancer agent because of its polo-like kinase 1 selectivity and effectiveness.

Quantitative analysis of cell-free DNA in the plasma of gastric cancer patients.

In the present study, an accurate and reproducible method for quantifying cell-free DNA (cfDNA) in human blood was established and tested for its ability to predict gastric cancer in patients. Using 'Alu81-qPCR' to amplify 81-bp Alu DNA sequences, we first estimated the amount of cfDNA in the serum or plasma of 130 patients with gastric cancer to identify which source of cfDNA is more suitable for the biomarker screening of these patients. The results of Alu81-qPCR revealed that the amount of cfDNA in the plasma was low compared with that in the serum, but was found at similar levels among the samples, indicating that the plasma may be a more suitable source of cfDNA for biomarker screening. For the 54 patients with gastric cancer and the 59 age-matched healthy controls, the mean levels of plasma cfDNA were 2.4-fold higher in the patient group compared with the control group, indicating that plasma cfDNA levels may be useful for predicting patients with gastric cancer. The results of our study suggest that Alu81-qPCR is a more reliable method than other techniques, such as the PicoGreen assay, for quantifying cfDNA in human blood, demonstrating the potential to complement current diagnostic procedures for the management of gastric cancer patients.

Epigenetic alteration of CCDC67 and its tumor suppressor function in gastric cancer.

In this study, the promoter of the gene coiled-coil domain-containing 67 (CCDC67) was found to be frequently methylated in gastric cancer cell lines and in primary gastric tumors, as examined by restriction landmark genomic scanning. In addition, CCDC67 expression was down-regulated in 72.7% of gastric cancer cell lines tested. In most cases, gene down-regulation was associated with CpG hypermethylation in the CCDC67 promoter. Treatment with 5-aza-2'-deoxycytidine and/or trichostatin A restored CCDC67 expression in down-regulated cell lines. Pyrosequencing analysis of 150 paired primary gastric cancer samples revealed that promoter CpG methylation was increased in 74% of tested tumors compared with paired adjacent normal tissues, and this hypermethylation correlated significantly with down-regulation of CCDC67. CCDC67 protein was localized to the cell membrane by immunocytochemistry. Stable transfection of a CCDC67 gene in one gastric cancer cell line inhibited adhesion-dependent and -independent colony formation, and CCDC67 expression suppressed tumorigenesis in nude mice. We suggest that CCDC67 is a putative tumor suppressor gene that is silenced in gastric cancers by promoter CpG methylation and that it may play an important role in cell signaling and migration related to tumorigenesis.

Frequent silencing of popeye domain-containing genes, BVES and POPDC3, is associated with promoter hypermethylation in gastric cancer.

The Popeye domain-containing (POPDC) genes BVES, POPDC2 and POPDC3 encode proteins that regulate cell-cell adhesion and cell migration during development. Herein, we report the frequent downregulation of BVES and POPDC3 by promoter hypermethylation in gastric cancer. POPDC expression in 11 gastric cancer cell lines and 96 paired gastric tumor and normal adjacent tissues was analyzed with quantitative reverse transcription-polymerase chain reaction. The methylation status of BVES and POPDC3 was analyzed with methylated DNA immunoprecipitation sequencing, bisulfite sequencing and pyrosequencing. Expression of BVES and POPDC3 was downregulated in 73% of the gastric cancer cell lines and in 69% (BVES) and 87% (POPDC3) of the gastric cancer tissues. The BVES and POPDC3 promoter regions were hypermethylated in the gastric cancer cell lines in which they were silenced. Combined treatment with a DNA methylation inhibitor and a histone deacetylase inhibitor strongly induced BVES and POPDC3 expression. BVES and POPDC3 were hypermethylated in 69% (BVES) and 64% (POPDC3) of the gastric cancer tissues. We knocked down POPDC3 expression with short hairpin RNAs and examined the consequences on cell migration and invasion. Knockdown of POPDC3 in SNU-216 cells caused increased cell migration and invasion. Thus, epigenetic inactivation of BVES and POPDC3 occurs frequently in gastric tumors and may promote gastric cancer cell migration and invasion.

LRRC3B, encoding a leucine-rich repeat-containing protein, is a putative tumor suppressor gene in gastric cancer.

Leucine-rich repeat-containing 3B (LRRC3B) is an evolutionarily highly conserved leucine-rich repeat-containing protein, but its biological significance is unknown. Using restriction landmark genomic scanning and pyrosequencing, we found that the promoter region of LRRC3B was aberrantly methylated in gastric cancer. Gastric cancer cell lines displayed epigenetic silencing of LRRC3B, but treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine and/or the histone deacetylase inhibitor trichostatin A increased LRRC3B expression in gastric cancer cell lines. Real-time reverse transcription-PCR analysis of 96 paired primary gastric tumors and normal adjacent tissues showed that LRRC3B expression was reduced in 88.5% of gastric tumors compared with normal adjacent tissues. Pyrosequencing analysis of the promoter region revealed that LRRC3B was significantly hypermethylated in gastric tumors. Stable transfection of LRRC3B in SNU-601 cells, a gastric cancer cell line, inhibited anchorage-dependent and anchorage-independent colony formation, and LRRC3B expression suppressed tumorigenesis in nude mice. Microarray analysis of LRRC3B-expressing xenograft tumors showed induction of immune response-related genes and IFN signaling genes. H&E-stained sections of LRRC3B-expressing xenograft tumors showed lymphocyte infiltration in the region. We suggest that LRRC3B is a putative tumor suppressor gene that is silenced in gastric cancers by epigenetic mechanisms and that LRRC3B silencing in cancer may play an important role in tumor escape from immune surveillance.

CpG methylation in exon 1 of transcription factor 4 increases with age in normal gastric mucosa and is associated with gene silencing in intestinal-type gastric cancers.

Transcriptional factor 4 (TCF4), encoding a basic helix-loop-helix transcriptional factor, has recently been demonstrated as a causative gene for Pitt-Hopkins syndrome, a neurodevelopmental disease. Examination of gastric cancers using the restriction landmark genomic scanning technique revealed methylation at a NotI enzyme site in TCF4 intron 8 and further identified CpG dinucleotide hypermethylation in TCF4 exon 1, strongly associated with gene silencing in gastric cancer cell lines. Treatment with 5-aza-2'-deoxycytidine and/or trichostatin A restored TCF4 expression in TCF4-silenced gastric cancer cell lines. Real-time reverse transcription-polymerase chain reaction analysis of 77 paired primary gastric tumor samples revealed that 38% of analyzed tumors had a >2-fold decrease in TCF4 expression compared with adjacent normal-appearing tissue, and the decrease significantly correlated with increased CpG methylation in TCF4 exon 1. Clinicopathologic data showed that decreased TCF4 expression occurred significantly more frequently in intestinal-type (22/37, 59%) than in diffuse-type (7/37, 19%) gastric cancers (P = 0.0004) and likewise more frequently in early (12/18, 67%) than in advanced (17/59, 29%) gastric cancers (P = 0.004). CpG methylation markedly increased with patient age among normal-appearing tissues, suggesting that CpG methylation in gastric mucosa may be one of the earliest events in carcinogenesis of intestinal-type gastric cancers. Furthermore, ectopic expression of TCF4 decreased cell growth in a gastric cancer cell line, and the knock down of TCF4 using small interfering RNA increased cell migration. Based on these results, we propose that the observed frequent epigenetic-mediated TCF4 silencing plays a role in tumor formation and progression.

Epigenetic down-regulation and suppressive role of DCBLD2 in gastric cancer cell proliferation and invasion.

The promoter region of Discoidin, CUB and LCCL domain containing 2 (DCBLD2) was found to be aberrantly methylated in gastric cancer cell lines and in primary gastric cancers, as determined by restriction landmark genomic scanning. DCBLD2 expression was inversely correlated with DCBLD2 methylation in gastric cancer cell lines. Treatment with 5-aza-2'-deoxycytidine and trichostatin A partially reversed DCBLD2 methylation and restored gene expression in DCBLD2-silenced cell lines. In an independent series of 82 paired gastric cancers and adjacent normal tissues, DCBLD2 expression was down-regulated in 79% of gastric cancers as compared with normal tissues as measured by real-time reverse transcription-PCR. Pyrosequencing analysis of the DCBLD2 promoter region revealed abnormal hypermethylation in gastric cancers, and this hypermethylation was significantly correlated with down-regulation of DCBLD2 expression. Furthermore, ectopic expression of DCBLD2 in gastric cancer cell lines inhibited colony formation in both anchorage-dependent and anchorage-independent cultures and also inhibited invasion through the collagen matrix. These data suggest that down-regulation of DCBLD2, often associated with promoter hypermethylation, is a frequent event that may be related to the development of gastric cancer.

Epigenetic inactivation of protein kinase D1 in gastric cancer and its role in gastric cancer cell migration and invasion.

Protein kinase D (PKD) 1 influences cell migration by mediating both trans-Golgi vesicle fission and integrin recycling to the cell surface. Using restriction landmark genomic scanning methods, we found that the promoter region of PKD1 was aberrantly methylated in gastric cancer cell lines. Silencing of PKD1 expression was detected in 72.7% of gastric cancer cell lines examined, and the silencing was associated with CpG hypermethylation in the promoter region of PKD1. Treatment with 5-aza-2'-deoxycytidine and trichostatin A partially reversed PKD1 methylation and restored gene expression in PKD1-silenced cell lines. Real-time reverse transcription-polymerase chain reaction analysis of 96 paired clinical primary gastric cancer samples revealed that 59% of the analyzed tumors had a >2-fold decrease in PKD1 expression compared with each normal-appearing tissue and that this downregulation of PKD1 expression was significantly correlated with increased methylation. We also observed a gradual increase in the level of promoter methylation of PKD1 in aging, normal-appearing mucosal tissues, suggesting that PKD1 methylation may be one of the earliest events that predispose an individual to gastric cancer. PKD1 expression was required for directional migration of gastric cancer cells. Furthermore, knock down of PKD1 by RNA interference promoted the invasiveness of cell lines that expressed PKD1 at relatively high levels. Based on these results, we propose that PKD1 is frequently silenced by epigenetic regulation, which plays a role in cell migration and metastasis in gastric cancer.