Gene structures of pepsinogens A and C

Identification of Novel Placentally Expressed Aspartic Proteinase in Humans

This study presents pioneering data concerning the human pregnancy-associated glycoprotein-Like family, identified in the genome, of the term placental transcriptome and proteome. RNA-seq allowed the identification of 1364 bp hPAG-L/pep cDNA with at least 56.5% homology with other aspartic proteinases (APs). In silico analyses revealed 388 amino acids (aa) of full-length hPAG-L polypeptide precursor, with 15 aa-signal peptide, 47 aa-blocking peptide and 326 aa-mature protein, and two Asp residues (D), specific for a catalytic cleft of the APs (VVFDTGSSNLWV91-102 and AIVDTGTSLLTG274-285). Capillary sequencing identified 9330 bp of the hPAG-L gene (Gen Bank Acc. No. KX533473), composed of nine exons and eight introns. Heterologous Western blotting revealed the presence of one dominant 60 kDa isoform of the hPAG-L amongst cellular placental proteins. Detection with anti-pPAG-P and anti-Rec pPAG2 polyclonals allowed identification of the hPAG-L proteins located within regions of chorionic villi, especially within the syncytiotrophoblast of term singleton placentas. Our novel data extend the present knowledge about the human genome, as well as placental transcriptome and proteome during term pregnancy. Presumably, this may contribute to establishing a new diagnostic tool for examination of some disturbances during human pregnancy, as well as growing interest from both scientific and clinical perspectives.

Progastriscin: structure, function, and its role in tumor progression

Progastricsin (PGC) is a major seminal plasma protein having aspartyl proteinases-like activity and showing close sequence similarity to pepsins. PGC is also present as zymogen in gastric mucosa. In this article, we have reviewed all important features of PGC. Furthermore, we have compared all features of PGC with those of different aspartyl proteinases. The complete amino acid sequence of PGC reveals that it is composed of 374 residues (gastricsin moiety of 331 residues and the activation segment of 43 residues). The gene of human PGC is located at single locus on chromosome 6, whereas the human pepsinogen genetic locus is polymorphic and codes for at least three distinct polypeptide sequences on chromosome 11. The major useful function of PGC includes production of pro-antimicrobial substance in seminal plasma. The crystal structure of human PGC is known, which shows that it is quite similar to that of porcine pepsinogen. The tertiary structure of PGC is comprised of commonly bilobal structure with a large active-site cleft between the lobes. Two aspartate residues in the center of the cleft, namely Asp32 and Asp215, function as catalytic residues. The sequence and structural features of PGC indicate that it is diverged from its pepsinogen ancestor in the early phase of the evolution of gastric aspartyl proteinases. Our detailed review of PGC structure, function and activation mechanism will also be of interest to cancer biologists as well as gastroenterologists.

Gastric adenocarcinoma with chief cell differentiation

A case of adenocarcinoma with chief cell differentiation, a novel entity in the stomach, is presented. An 82-year-old woman who had undergone distal gastrectomy, was scheduled for upper gastrointestinal endoscopy to clarify mechanical ileus. A protruding tumor 16 x 14 x 9 mm in size was found in the cardia of the remnant stomach. Histological examination indicated a well-differentiated tubular adenocarcinoma composed of basophilic columnar or cuboidal cells with occasional coarse eosinophilic granules. Immunohistochemical analysis revealed strong expression of pepsinogens I and II and Runt-related transcription factor gene 3 (RUNX3), characteristic for chief cells, and MUC6 typical for mucous neck cells. However, the tumor cells were negative for the proton pump alpha subunit, a marker for parietal cells. Cdx2 and defensin-5 were not present, confirming the lack of an intestinal phenotype. The cancer cells shared characteristics of a chief cell and a mucous neck cell, resembling an ancestor of these two cell types, so-called 'primitive chief cell' in fundic gland. In line with these data, the cancer was diagnosed as an adenocarcinoma with chief cell differentiation.

Effect of smoking on serum pepsinogen I level depends on serological status of Helicobacter pylori

Serum pepsinogen (sPG) levels are used in gastric cancer screening programs. However, modification of sPG levels by smoking habit, according to the status of Helicobacter pylori (H. pylori) infection has been little investigated. This study investigated the effects of smoking on serum levels of pepsinogen I (PG I), pepsinogen II (PG II), and gastrin by IgG titer of antibody against H. pylori (Hp-IgG titer) using the data from 356 current-smokers and 262 non-smokers (133 never-smokers and 129 ex-smokers) in a cross-sectional study of 618 men aged 40 to 49 years. PG I, PG II, PG I / PG II ratio and gastrin were significantly associated with Hp-IgG titer in never-smokers [Spearman's correlation coefficient (95% confidence interval): 0.23 (0.07, 0.39), 0.52 (0.41, 0.63), -0.40 (-0.54,-0.27), and 0.25 (0.10, 0.41), respectively]. However, the correlation coefficients of PG I and PG II decreased in current-smokers, 0.02 (-0.1, 0.13) and 0.32 (0.22, 0.42), respectively. In H. pylori seronegative and low titer cases, the mean PG I level was significantly (P < 0.01) higher in current-smokers, compared with non-smokers. However, in high titer cases, the mean PG I level was lower in current-smokers. Mean PG II and gastrin levels, and PG I / PG II ratio did not differ according to smoking habits by Hp-IgG titer. The gastrin level was significantly correlated with PG II, but not PG I. These data indicate that current smoking influences the serum PG I level depending on Hp-IgG titer and the associations between sPGs and Hp-IgG titer. Gastrin is not involved in the modification of PG I levels by smoking.

Pepsinogen C gene product is a possible growth factor during gastric mucosal healing

We isolated, by the subtraction cloning method, a pepsinogen C (PGC) gene fragment (the sequence between the 968th and 1179th base pairs) from a rat gastric mucosal cDNA library as a cDNA clone encoding a substance that promotes growth of the normal rat gastric mucosal cell line RGM1. Northern blot analysis revealed that PGC gene expression was enhanced not only in acetic acid-induced chronic gastric ulcers but also in indomethacin-induced gastric mucosal lesions. PGC gene expression was also increased in the Helicobacter felis-infected stomachs. Thus, the PGC gene may play a role in gastric epithelial cell growth during gastric mucosal healing.

Absence of pepsinogen A3 gene expression in the gastric mucosa of patients with gastric cancer

AIMS

To investigate the expression of pepsinogen A3 (Pg3) encoding genes in the gastric mucosa of normal controls and subjects with atrophic gastritis and gastric cancer.

METHODS

One hundred and fifty nine patients underwent upper gastrointestinal endoscopy with sampling of gastric biopsy specimens and serum. Pg3 isoproteins were determined by electrophoresis in serum and gastric mucosal biopsy specimens. Pg3 encoding genes were assessed by PCR in DNA obtained from peripheral blood.

RESULTS

One hundred and one subjects (82 normal histology/chronic gastritis, 17 atrophic gastritis, two gastric cancer) showed a pepsinogen phenotype with presence of Pg3 and a corresponding pepsinogen genotype with presence of Pg3 encoding genes. Fifty eight subjects showed a phenotype lacking Pg3. In 39 of them (23 normal histology/chronic gastritis, 11 atrophic gastritis, five gastric cancer), a corresponding genotype without Pg3 encoding genes was found. However, in the remaining 19 subjects (4 normal histology/chronic gastritis, nine atrophic gastritis, six gastric cancer); Pg3 encoding genes were demonstrable in the absence of Pg3 production.

CONCLUSIONS

Unexpressed Pg3 encoding genes can be shown in many cases of atrophic gastritis and gastric cancer, but rarely in healthy controls and subjects with superficial gastritis. The correlation of atrophic gastritis and gastric cancer with a pepsinogen phenotype lacking Pg3 can be explained by loss of expression of Pg3 encoding genes throughout the complete gastric mucosa. The mechanism of such loss and the importance as a marker for premalignant degeneration have to be elucidated.