Increased expression of deleted in malignant brain tumors (DMBT1) gene in precancerous gastric lesions: Findings from human and animal studies

Abstract

Helicobacter pylori infection triggers a cascade of inflammatory stages that may lead to the appearance of non-atrophic gastritis, multifocal atrophic, intestinal metaplasia, dysplasia, and cancer. Deleted in malignant brain tumors 1 (DMBT1) belongs to the group of secreted scavenger receptor cysteine-rich proteins and is considered to be involved in host defense by binding to pathogens. Initial studies showed its deletion and loss of expression in a variety of tumors but the role of this gene in tumor development is not completely understood. Here, we examined the role of DMBT1 in gastric precancerous lesions in Caucasian, African American and Hispanic individuals as well as in the development of gastric pathology in a mouse model of H. pylori infection. We found that in 3 different populations, mucosal DMBT1 expression was significantly increased (2.5 fold) in individuals with dysplasia compared to multifocal atrophic gastritis without intestinal metaplasia; the increase was also observed in individuals with advanced gastritis and positive H. pylori infection. In our animal model, H. pylori infection of Dmbt1-/- mice resulted in significantly higher levels of gastritis, more extensive mucous metaplasia and reduced Il33 expression levels in the gastric mucosa compared to H. pylori-infected wild type mice. Our data in the animal model suggest that in response to H. pylori infection DMBT1 may mediate mucosal protection reducing the risk of developing gastric precancerous lesions. However, the increased expression in human gastric precancerous lesions points to a more complex role of DMBT1 in gastric carcinogenesis.

Keywords: DMBT1; H. pylori; gastric cancer; inflammation; precancerous gastric lesions.

Figure 1. Increased DMBT1 expression in gastritis and precancerous lesions

(A) Hispanic individuals with dysplasia have increased levels of DMBT1 when compared to individuals with MAG (*p=0.0051). (B) African American (AA) and Caucasian (CA) individuals with NAG or MAG-IM (combined MAG and IM) show increased gastric levels of DMBT1 mRNA when compared to individuals with normal gastric mucosa from either ethnic group. *p=0.0058; **p<0.0001 when compared to AA normal; #p=0.0001; ##p<0.001 when compared to CA normal. Median and interquartile range are shown. (C) Representative IHC for DMBT1 expression in normal, NAG, and IM.

Figure 2. Expression of DMBT1 is associated with H. pylori infection

Expression of DMBT1 from gastric tissue RNA from African American individuals with different stages of gastric lesions was analyzed by real-time PCR. Infection with H. pylori was determined by Steiner silver stain as described in Materials and Methods. All subjects with normal gastric mucosa were uninfected. *p=0.007 when compared to Normal; Hp, H. pylori. Median and interquartile range are shown.

Figure 3. H. pylori infection induces premalignant lesions and more severe inflammation in Dmbt1−/− mice

(A) Semiquantitative scores of the inflammatory infiltrate in the gastric mucosae of Dmbt1−/− and WT mice 4 months after inoculation with H. pylori SS1; *p=0.048. (B) Metaplastic changes in the mucosae of the gastric corpus of H. pylori-infected Dmbt1−/− and WT mice were scored from 0 to 3 as described in Materials and Methods; **p=0.0065. (C) Representative images of sections of the gastric corpus of non-infected and H. pylori-infected Dmbt1−/− and WT mice showing more severe pseudo-pyloric metaplasia in H. pylori-infected Dmbt1−/− mice compared to H. pylori-infected WT mice. H&E stains at 100X magnification. (D) Representative images of the AB-PAS stains of gastric mucosa sections of H. pylori-infected WT and Dmbt1−/− mice showing the presence of mucous metaplasia in Dmbt1−/− mice (100X magnification). Median and interquartile range are shown.

Figure 4. Enhanced proliferation of gastric epithelial cells in Dmbt1−/− mice following H. pylori infection

(A) Representative images of Ki67 labelling of gastric mucosa sections of non-infected and H. pylori-infected WT and Dmbt1−/− mice. (B) Ki67-labeledproliferatingcells were counted in 10 well-oriented and randomly selected glands of the gastric corpus; *p=0.042, **p=0.004, compared to the respective non-infected counterpart. Median and interquartile range are shown.

Figure 5. Decreased expression of IL-33 in H. pylori infected Dmbt1−/− mice

(A) Comparison of mRNA levels of Il33 in the gastric mucosae of Dmbt1−/− and WT mice following 4 months of infection with H. pylori. Results are shown as fold induction relative to Gapdh expression. * p=0.046; **p=0.0043; ^#p=0.0496. (B) pERK expression score was assessed using immunohistochemistry in the gastric mucosae of Dmbt1−/− and WT mice infected with H. pylori for 4 months as described in Material and Methods. *p=0.095; **p=0.0079. Median and interquartile range are shown. (C) Representative images of anti-pERK immunohistochemistry on gastric mucosa sections of non-infected and H. pylori-infected WT and Dmbt1−/− mice.