Abstract
BackgroundDysregulated histone methyltransferase G9a may represent a potential cancer therapeutic target. The roles of G9a in tumorigenesis and therapeutics are not well understood in non-small cell lung cancer (NSCLC). Here we investigated the impact of G9a on tumor growth and signaling pathways in NSCLC.MethodsImmunohistochemistry analyzed G9a expression in NSCLC tissues. Both siRNA and selective inhibitor were used to target G9a. The impact of targeting G9a on key genes, signaling pathways and growth were investigated in NSCLC cells by RNA sequencing analysis, rescue experiments, and xenograft models.ResultsOverexpression of G9a (≥ 5% of cancer cells showing positive staining) was found in 43.2% of 213 NSCLC tissues. Multiple tumor-associated genes including HP1α, APC2 are differentially expressed; and signaling pathways involved in cellular growth, adhesion, angiogenesis, hypoxia, apoptosis, and canonical Wnt signaling pathways are significantly altered in A549, H1299, and H1975 cells upon G9a knockdown. Additionally, targeting G9a by siRNA-mediated knockdown or by a selective G9a inhibitor UNC0638 significantly inhibited tumor growth, and dramatically suppressed Wnt signaling pathway in vitro and in vivo. Furthermore, we showed that treatment with UNC0638 restores the expression of APC2 expression in these cells through promoter demethylation. Restoring HP1α and silencing APC2 respectively attenuated the inhibitory effects on cell proliferation and Wnt signaling pathway in cancer cells in which G9a was silenced or suppressed.ConclusionsThese findings demonstrate that overexpressed G9a represents a promising therapeutic target, and targeting G9a potentially suppresses growth and Wnt signaling pathway partially through down-regulating HP1α and epigenetically restoring these tumor suppressors such as APC2 that are silenced in NSCLC.
Highlights
Dysregulated histone methyltransferase G9a may represent a potential cancer therapeutic target
We first examined aberrant G9a expression and deciphered its transcriptional regulatory network and highlighted its complex role in gene expression, and we found that The adenomatous polyposis coli-2 (APC2) was dramatically upregulated upon G9a knockdown, while heterochromatin protein 1 alpha (HP1α), which binds euchromatic loci during the process of gene silencing in cooperation with DNA methyltransferase 1 (DNMT1) [25], was significantly downregulated
Suppression of Wnt activation through de-repressing APC2 via promoter demethylation by UNC0638 treatment in non-small cell lung cancer (NSCLC) cells By RNA sequencing (RNA-Seq), we found that APC2, which forms a destructive complex capable of binding β-catenin to function as an important inhibitor of Wnt signaling pathway [34], was dramatically upregulated upon G9a knockdown, suggesting that targeting G9a would restore these genes silenced by epigenetic machinery
Summary
Dysregulated histone methyltransferase G9a may represent a potential cancer therapeutic target. The roles of G9a in tumorigenesis and therapeutics are not well understood in non-small cell lung cancer (NSCLC). We investigated the impact of G9a on tumor growth and signaling pathways in NSCLC. Lung cancer is the leading cause of cancer-related death worldwide [1]. About 85% of lung cancers are non-small cell lung cancer (NSCLC), while lung adenocarcinoma roughly accounts for about 50% of NSCLC [1]. There have been advances in targeted therapies and immunotherapy, the 5-year survival rate for NSCLC patients remains only 15% [2]. Recent studies have uncovered an important role for epigenetic changes in tumor progression and treatment resistance [3, 4]. Studies have revealed that G9a is overexpressed in a number of cancers, including esophageal squamous cell carcinoma, hepatocellular carcinoma, brain cancer, multiple myeloma, and aggressive ovarian carcinoma; and overexpressed G9a is found to be associated with enhanced proliferation and metastasis of various cancer cells [7, 8]
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