INTERNATIONAL JOURNAL OF ONCOLOGY 55: 555-569, 2019 Regulation of GKN1 expression in gastric carcinogenesis: A problem to resolve (Review) JUDIT ALARCÓN‑MILLÁN1, DINORAH NASHELY MARTÍNEZ‑CARRILLO1, OSCAR PERALTA‑ZARAGOZA2 and GLORIA FERNÁNDEZ‑TILAPA1 1Clinical Research Laboratory, Faculty of Biological Chemical Sciences, Guerrero Autonomous University, Chilpancingo, Guerrero 39070; 2Direction of Chronic Infections and Cancer, Research Center in Infection Diseases, National Institute of Public Health, Cuernavaca, Morelos 62100, México Received January 11, 2019; Accepted July 4, 2019 DOI: 10.3892/ijo.2019.4843 Abstract. Gastrokine 1 (GKN1) is a protein expressed on the Contents surface mucosa cells of the gastric antrum and fundus, which contributes to maintaining gastric homeostasis, inhibits 1. Introduction inflammation and is a tumor suppressor. The expression of 2. GKN1 GKN1 decreases in mucosa that are either inflamed or infected 3. GKN1, H. pylori infection and gastric cancer by Helicobacter pylori, and is absent in gastric cancer. The 4. GKN1 as a potential biomarker of gastric carcinogenesis measurement of circulating GKN1 concentration, the protein 5. Regulation of GKN1 expression in mucous infected by itself, or the mRNA in gastric tissue may be of use for the H. pylori or with gastric cancer early diagnosis of cancer. The mechanisms that modulate the 6. Conclusion deregulation or silencing of GKN1 expression have not been completely described. The modification of histones, methyla- tion of the GKN1 promoter, or proteasomal degradation of 1. Introduction the protein have been detected in some patients; however, these mechanisms do not completely explain the absence The gastric epithelium is continually renewed over a lifetime, of GKN1 or the reduction in GKN1 levels. Only NKX6.3 and is maintained through the proliferation and differentia- transcription factor has been shown to be a positive modu- tion of pluripotent stem cells from the isthmus of the gastric lator of GKN1 transcription, although others also have an gland (1). Stem cells generate precursors that migrate to the affinity with sequences in the promoter of this gene. While gastric lumen and, in turn, generate parietal, gastric zymogenic microRNAs (miRNAs) are able to directly or indirectly and foveolar cells. Parietal cells produce hydrochloric acid, regulate the expression of genes at the post-transcriptional while gastric zymogenic cells have a half‑life of ~6 months level, the involvement of miRNAs in the regulation of GKN1 and synthesize trefoil factor 2 and mucin 6 (1‑3). Foveolar cells has not been reported. The present review analyzes the infor- or surface mucous cells (SMCs), whose half‑life is 2‑3 days, mation reported on the determination of GKN1 expression produce mucous granules, mucin 5AC, gastrokine 1 (GKN1) and the regulation of its expression at the transcriptional, and trefoil factor 1 (1‑3) and play an important role in the resti- post-transcriptional and post-translational levels; it proposes tution of the gastric mucosa in the event of Helicobacter pylori an integrated model that incorporates the regulation of infection (4). The integrity and continuity of the gastric GKN1 expression via transcription factors and miRNAs in epithelium are rapidly restored after damage, prior to cell H. pylori infection. proliferation (5). Epithelial restitution is achieved through the migration of epithelial cells from the adjacent area or the cell stratum below the surface cells in the injured area. Epithelial cell restitution in the stomach of mammals takes place in minutes (5). Correspondence to: Dr Gloria Fernández‑Tilapa, Clinical Research Laboratory, Faculty of Biological Chemical Sciences, GKN1 is a protein secreted by SMCs of the gastric antrum Guerrero Autonomous University, Avenida Lázaro Cárdenas S/N, and fundus (6), which contributes to maintaining gastric Col. Haciendita, Chilpancingo, Guerrero 39070, México homeostasis, inhibits inflammation and acts as a tumor E‑mail: [email protected] suppressor (7‑16). The expression of GKN1 decreases due to H. pylori infection, inflammation or atrophy, and is absent in Key words: gastrokine 1, regulation, microRNAs, transcription gastric cancer (17‑25). factors, Helicobacter pylori, gastric cancer Although methylation of the GKN1 promoter (20), modifi- cation of histones (26) and proteasomal degradation of GKN1 in some cases (27) have been reported, the mechanisms that 556 ALARCÓN‑MILLÁN et al: REGULATION OF GASTROKINE 1 EXPRESSION cause a decrease in GKN1 levels or its absence entirely have In the normal gastric mucosa, GKN1 is expressed by epithe- not been completely described. A total of ~10% of gastric lial cells on the surface, but not at the depth of the glands of the tumors contain the Epstein-Barr virus (EBV), while the gastric mucosa (21,45,46). GKN1 reduces the expression of the Epstein-Barr nuclear antigen 1 (EBNA1) binds to the promoter gastrin receptor, gastrin/cholecystokinin type B receptor, thus region of the GKN1 gene and induces the reduction of its tran- inhibiting the cell proliferation induced by this hormone (13). scription (28,29). GKN1 activates the p16/Rb and p21 signaling pathways, Epigenetic modifications are as important to the regu- inhibits cell growth and drives cells to senescence (46). GKN1 lation of gene expression and the initial stages of disease modulates the expression of cytokines and other inflammatory as genetic modifications. Differential changes have been mediators associated with gastric carcinogenesis, inducing documented in the expression profile of microRNAs the increased expression of interleukin (IL)‑8 and IL‑17 and (miRNAs) in gastritis or cancer patients infected with the decreased expression of nuclear factor (NF)-κB, IL-6 and H. pylori (17,30‑33), gastric cancer cell lines (34‑36), CD4 IL‑10. Thus, it regulates the immune response and inhibits the T lymphocytes, macrophages, monocytes and dendritic progression of epithelial gastric cells to cancerous cells. GKN1 cells (37‑39). It has been proposed that some components suppresses the activation of NF-κB, and thus inhibits the onco- of H. pylori induce the activation of signals that modify the genic signaling regulated by this transcription factor (9). expression of miRNAs in the host cells, and that changes in the global expression profile of miRNAs are related to the 3. GKN1, H. pylori infection and gastric cancer genotype of the bacteria (31). The reduction of GKN1 cannot be explained by mutations GKN1 and H. pylori infection. Infection with H. pylori cagA+ in its gene, the methylation of its promoter or the protea- strains increases the risk of gastric cancer and is related to somal degradation of the protein (20,26,27). It is probable the reduced expression of GKN1 in the mucosa (47). In mice that some miRNAs modulate the decreased translation of infected with H. pylori‑cagA+, the increased expression of GKN1 mRNA and, consequently, the reduction of the level the antiapoptotic proteins Bcl‑2, Bcl‑XL and induced myeloid of protein in the gastric mucosa. The role of miRNAs in the leukemia cell differentiation protein Mcl‑1, as well as NF‑κB regulation of GKN1 expression in the normal gastric mucosa, and proteins related to EMT, is found, while the expression or mucosa infected with H. pylori, affected by preneoplasic of p53, p21, p16 and stress response genes decreases (48). lesions or with gastric cancer, has not been explored. The The ectopic expression of GKN1 suppresses the effects of present review comprises an analysis of the information H. pylori‑cagA+ in the human gastric cancer cell lines AGS, published on the regulation of GKN1 expression, proposing MKN1 and MKN28. Based on these findings, it has been a model that integrates the probable regulatory mechanisms suggested that GKN1 suppresses the malignant transforma- at the transcriptional, post-transcriptional and translational tion of gastric epithelial cells and the progression to gastric levels. cancer (48). The expression of GKN1 decreases at the mRNA and 2. GKN1 protein levels in dyspeptic patients and is not detected in the mucosa of subjects with intestinal-type gastric cancer, both GKN1 (also known as CA11, AMP‑18, foveolin or TFIZ2) is a with and without H. pylori infection (19,20,21,22,30,49‑52), or small protein of 181‑184 amino acids, specifically expressed in with a diffuse‑type cancer (19,23,25). the stomach. The GKN1 gene is located on chromosome 2p13.3 and is composed of six exons separated by relatively short GKN1 and gastric cancer. GKN1 is absent in human gastric introns (6). GKN1 is composed of: i) A hydrophobic signal tumors and acts as a tumor suppressor, regulating cell prolif- peptide in the extreme NH2-terminal, whose processing gener- eration, apoptosis, migration and invasion in gastric cancer ates a protein of 160 amino acids with a molecular mass of cell lines (10). Stimulating the expression of Fas receptor and 18 kDa; ii) a BRICHOS domain with three conserved amino the activation of caspase‑3, this protein modulates apoptotic acid residues, one aspartic acid residue and two cysteine acid signals, playing an important role in the repair of tissues residues; and iii) a COOH‑terminal domain (6,19,40‑43). during the early stages of neoplastic transformation (7). GKN1 is a member of the BRICHOS superfamily of proteins, In AGS, MKN‑1 and MKN‑28 gastric cancer cell lines which includes proteins associated with the development of transfected with GKN1, the re-expression of p16 and a reduc- cancer. It is a protein