Hypoxic silencing of tumor suppressor RUNX3 by histone modification in gastric cancer cells

Abstract

RUNX3 is a tumor suppressor that is silenced in cancer following hypermethylation of its promoter. The effects of hypoxia in tumor suppressor gene (TSG) transcription are largely unknown. Here, we investigated hypoxia-induced silencing mechanisms of RUNX3. The expression of RUNX3 was downregulated in response to hypoxia in human gastric cancer cells at the transcriptional level. This downregulation was abolished following treatment with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) and cytosine methylation inhibitor 5-aza-2-deoxycytidine (5-Aza), suggesting that an epigenetic regulatory mechanism may be involved in RUNX3 silencing by hypoxia. DNA methylation PCR and bisulfite-sequencing data revealed that hypoxia did not affect the methylation of RUNX3 promoter. A chromatin immunoprecipitation (ChIP) assay revealed increased histone H3-lysine 9 dimethylation and decreased H3 acetylation in the RUNX3 promoter following hypoxia. Hypoxia resulted in the upregulation of G9a histone methyltransferase (HMT) and HDAC1; additionally, overexpression of G9a and HDAC1 attenuated RUNX3 expression. The overexpression of G9a and HDAC1, but not their mutants, inhibited the nuclear localization and expression of RUNX3. Diminished mRNA expression and nuclear localization of RUNX3 during hypoxia was abolished by siRNA-mediated knockdown of G9a and HDAC1. This study suggests that hypoxia silences RUNX3 by epigenetic histone regulation during the progression of gastric cancer.

RUNX3 is multifunctional in carcinogenesis of multiple solid tumors

“…In the same vein, Fujii et al (2008) found that EZH2 binds to the RUNX3 promoter, resulting in upregulation of H3K27 methylation and concomitant downregulation of RUNX3 expression (Fujii et al, 2008). Recently, Lee et al (2009) extended this finding by showing that hypoxia-induced upregulation of G9a histone methyltransferase and HDAC1 expression also cause epigenetic RUNX3 silencing through H3K9 methylation and decreased H3 acetylation at RUNX3 promoter. As hypoxia is commonly associated with solid tumors of 41 mm 3 , this suggests that RUNX3 inactivation may be associated with increased tumor size .…”

Inhibition of Histone Deacetylase Attenuates Hypoxia-Induced Migration and Invasion of Cancer Cells via the Restoration of RECK Expression

“…After the cells were fixed with 4% paraformaldehyde, immunofluorescence was done as previously described (14). The slides were examined under fluorescence microscopy at 400× magnification (Carl Zeiss).…”

“…Hypoxia silences tumor suppressors, such as MLH1 (13), RUNX3 (14), and pVHL (10), by epigenetic mechanisms, such as histone modification. Hypoxia activates genetic programs that facilitate cellular adaptations (e.g., changes in cell signaling and gene expression) and promotes cell survival, cell migration, invasion, metastasis, and resistance to chemotherapy (15).…”

Hypoxia-Inducible Factor 1 Promoter-Induced JAB1 Overexpression Enhances Chemotherapeutic Sensitivity of Lung Cancer Cell Line A549 in an Anoxic Environment

“…And, oncogene was markedly up-regulated (Bando et al, 2003), while tumor suppressor gene was significantly down-regulated in a hypoxic condition (Lee et al, 2009).…”