Pepsinogen secretion in vitro

Hepatocyte growth factor regulates the development of highly pure cultured chief cells from rat stomach by stimulating chief cell proliferation in vitro

The physiology of gastric epithelial cells is often studied by using cancer cell lines, which may or may not provide information relevant to normal cells. Because few models exist to study chief cell physiology in vitro, our purpose was to develop primary cultured chief cells from rodent species that are structurally and functionally similar to native chief cells. For this, isolated chief cells from the rat stomach, purified by counterflow elutriation and density gradient centrifugation, were grown in media with growth factors. Purity and the continuity of tight junctions were determined, and permeability, viability, transepithelial resistance (TER), cell number and proliferation, and pepsinogen secretion in response to carbachol were measured. When plated in media alone or with basic fibroblast growth factor, the isolated chief cells attached by 2 days and were confluent by 4 days after seeding. However, tight junctions were discontinuous, TER was less than 300 Omega cm(2), and permeability was high. In contrast, chief cells incubated with hepatocyte growth factor (HGF) were confluent in 3 days and had a TER greater than 2,000 Omega cm(2), continuous tight junctions, and low permeability. EGF was intermediate. HGF facilitated monolayer development by increasing cell number, which occurred by the proliferation of chief cells. Chief cell cultures, grown with HGF, consisted of more than 99% gastric intrinsic factor-expressing cells and showed robust pepsinogen secretion. Coexpression studies for neck and chief cell markers suggest that the cultures are a mixture of mature, immature, and transitional zone cells. This model will be useful for investigating mechanisms that regulate chief cell physiology in health and disease.

Pepsin-inhibitory activity of the uterine serpins

Among the major products secreted by the uteri of cattle, sheep, and pigs during pregnancy are glycoproteins with amino acid sequences that place them in the serpin (serine proteinase inhibitor) superfamily of proteins. The inferred amino acid sequences for bovine uterine serpin (boUS-1) and ovine uterine serpin (ovUS-1) exhibit about 72% sequence identity to each other but only about 50% and 56% identity, respectively, to two distinct porcine uterine serpins (poUS-1 and poUS-2). Despite these differences in primary structure, the uterine serpins possess well-conserved reactive center loop regions that contain several motifs present in the propeptide regions of pepsinogens. One such motif, VVVK, aligns with the first 4 amino acids of the aspartic proteinase inhibitor pepstatin. Although no inhibitory activity toward any serine proteinase has been found, at least one of the uterine serpins, ovUS-1, can bind specifically to immobilized pepsin A and can weakly inhibit the proteolytic activities of pepsin A and C (but not cathepsins D and E). OvUS-1 is the first specific inhibitor of aspartic proteinases to be identified in vertebrates and provides another example of a serpin with "crossover" activity. The pregnancy-associated glycoproteins (PAGs), which are secreted by the trophoblast layer of the placentas of ungulate species and are inactive members of the aspartic proteinase family, can also bind ovUS-1 and may be the natural target partners for the uterine serpins.