Glutathione peroxidase 7 has potential tumour suppressor functions that are silenced by location-specific methylation in oesophageal adenocarcinoma

Abstract

Objective We investigated the potential tumor suppressor functions of glutathione peroxidase 7 (GPX7) and examined the interplay between epigenetic and genetic events in regulating its expression in oesophageal adenocarcinomas (OAC). Design In vitro and in vivo cell models were developed to investigate the biological and molecular functions of GPX7 in OAC. RESULTS Reconstitution of GPX7 in OAC cell lines, OE33 and FLO-1, led to significant growth suppression as demonstrated by growth curve, colony formation and EdU proliferation assays. Meanwhile, GPX7-expressing cells displayed significant impairment in G1/S progression and an increase in cell senescence. Concordant with the above functions, Western blot analysis displayed higher levels of p73, p27, p21, and p16 with a decrease in phosphorylated RB; indicating its increased tumor suppressor activities. On the contrary, knockdown of GPX7 in HET1A cells (an immortalized normal esophageal cell line) rendered the cells growth advantage as indicated with a higher EdU rate, lower levels of p73, p27, p21, and p16 and an increase in phosphorylated RB. We confirmed the tumor suppressor function in vivo using GPX7-expressing OE33 cells in a mouse xenograft model. Pyrosequencing of the GPX7 promoter region (−162 to +138) demonstrated location-specific hypermethylation between +13 and +64 in OACs (69%, 54/78). This was significantly associated with the downregulation of GPX7 (p<0.01). Neither mutations in the coding exons of GPX7 nor DNA copy number losses were present in the OACs examined (<5%). CONCLUSIONS Our data suggest that GPX7 possesses tumor suppressor functions in OAC and is silenced by location-specific promoter DNA methylation.

Glutathione Peroxidase 7 Suppresses Bile Salt-Induced Expression of Pro-Inflammatory Cytokines in Barrett's Carcinogenesis

“…We have recently reported that GPX7 protects esophageal epithelia from acidic bile salts-induced oxidative DNA damage and double strand breaks through modulating intracellular ROS 20. We also demonstrated that GPX7 has a tumor suppressor function that is silenced through location specific DNA hypermethylation in Barrett's carcinogenesis 23. In the present study, we show that GPX7 can suppress the bile salts-induced activation of NF-κB and up-regulation of pro-inflammatory, pro-tumor cytokines and chemokines, further supporting a tumor suppressor function of GPX7 in EAC.…”

“…We have previously shown that GPX7 plays a tumor suppressor function in esophageal adenocarcinoma 23. Aberrant activation of NF-κB has been associated with inflammation and tumor development and progression 11, 30, 31.…”

“…We have previously reported that GPX7 is frequently silenced in Barrett's carcinogenesis through location-specific promoter DNA hypermethylation 23, 24. We next examined if the loss of GPX7 expression correlates with the major pro-inflammatory cytokines associated with NF-κB activation in EAC.…”

Genetic and epigenetic regulation of gene expression in fetal and adult human livers

“…Glutathione peroxidases (GPX) constitute a major antioxidative damage enzyme family [ 43 ] and are thus important in cancer therapy [ 44 ]. Not only genetic but also epigenetic mechanisms of gene regulation have been proposed for GPX7 , while recently a CpG island was identified as a key player in regulating GPX7 expression [ 45 ]. In total, we identified 87 SNPs in the GPX7 gene affecting the methylation of nine CpG sites (meQTL), with six of the sites being directly implicated in quantitative differences in the gene expression.…”

Transit of H2O2 across the endoplasmic reticulum membrane is not sluggish

“…Other examples, which are connected to H 2 O 2 transit across the ER membrane, are granulocyte colonystimulating factor receptor signaling [29], oxidative DNA damage in response to cellular stresses [30][31][32], activation of survival pathways upon H 2 O 2 generation in the ER [33,34], and the regulatory roles of ER-luminal peroxidases in various settings of cytosolic signal transduction [29,[35][36][37][38]. These findings clearly indicate the permeability of the ER membrane for H 2 O 2 .…”