Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.108 (lactase)
 2,133 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression and cellular localization of brush-border enzymes (aminopeptidase N, dipeptidylpeptidase IV, lactase, maltase) in normal human colon, colonic polyps and malignant intestinal tumors were investigated with a panel of monoclonal antibodies reacting with either native or denatured proteins. The enzymes were detected on cryostat sections by indirect immunofluorescence staining, or affinity-purified and analyzed by gel electrophoresis and immunoblotting. Dipeptidylpeptidase IV, lactase and maltase were absent from all samples examined, while aminopeptidase N (APN) was detected at the basal membrane of the epithelial cells in most specimens of colon obtained from individuals free of intestinal tumors. In contrast, APN was frequently localized at the luminal membrane of the surface epithelium in large-intestinal mucosa distal to tumors, adenomas and hyperplastic polyps, and from members of hereditary colon cancer syndrome families. APN was also expressed in colonic tumors, where it was present in an apical cell membrane location in 3/23 adenomas and 14/35 adenocarcinomas examined. No correlation was found between tumor-cell invasiveness (classified by "Dukes" stage) and expression or cellular location of aminopeptidase N. Histologically, all positive tumors were moderately or well differentiated. These results suggest that aminopeptidase N is normally expressed in adult human colon, but epithelial cells in the large and small intestine differ in their ways of sorting this enzyme intracellularly and eventually inserting it into different aspects of their surface membrane, a process which may be altered at an early stage of carcinogenesis.
 ...
PMID:Expression and different polarity of aminopeptidase N in normal human colonic mucosa and colonic tumors. 137 88

To investigate the biosynthetic basis for the mosaic expression of brush border enzymes in confluent Caco-2 cells, a human colon carcinoma cell line exhibiting characteristics of adult small intestinal enterocytes, we have obtained a series of clones differing markedly in their growth rates, amounts of transforming growth factor-alpha/epidermal growth factor-like activity released into the culture medium, and sucrase-isomaltase (SI) activity. Other intestinal markers (aminopeptidase N, dipeptidylpeptidase IV, lactase, alkaline phosphatase and 'crypt cell antigen') displayed a much more limited variability in expression, suggesting that the Caco-2 cell clones we have obtained did not differ in their overall ability to differentiate. Immunofluorescence staining, metabolic labelling with radioactive methionine and hybridization analysis of SI mRNA abundance were used to investigate SI synthesis and its regulation in clones endowed with low, intermediate or high sucrase activity. The results obtained have demonstrated heterogeneous SI expression, even in clonal cell lines, and a negative correlation between SI expression and growth factor concentrations in the culture medium, suggesting an autocrine regulation of cell proliferation and differentiation in confluent Caco-2 cells. Pulse-chase experiments using the two clones endowed with the lowest and highest levels of SI activity, followed by immunoprecipitation of labelled SI with epitope-specific antibodies and SDS/PAGE analysis, suggested that both transcriptional and post-translational mechanisms play a role in the regulation of SI expression in intestinal cells.
 ...
PMID:Clonal analysis of sucrase-isomaltase expression in the human colon adenocarcinoma Caco-2 cells. 176 23

1. Change in digestive enzyme activities determined biochemically in brush-border membrane vesicles and cytochemically in isolated villi of lamb proximal intestine has been related to diet, intestinal structure and rumen development during the first 10 weeks of postnatal life. 2. Lactase activity halved, dipeptidylpeptidase IV activity doubled and aminopeptidase N and alkaline phosphatase activities remained constant during this period of development. Maintaining lambs on a milk replacer diet for 5 weeks after birth had no effect on this pattern of postnatal change in digestive enzyme activities. 3. Structural changes accompanying these selective effects on enzyme expression included a halving of villus height and a doubling of villus width. Villus surface area remained unaffected by these changes in height and width of villi. Crypt depth doubled during the first 10 weeks of postnatal life. Maintaining lambs on a milk replacer diet for 5 weeks did not affect this pattern of change in intestinal structure. 4. It appears from these results that postnatal decrease in lactase and increase in dipeptidylpeptidase IV activities are not regulated by factors such as diet, rumen development, or changes in intestinal structure. Attention is drawn to differences encountered between these results and a postnatal modification of glucose transport which clearly is dependent on diet.
 ...
PMID:Postnatal development of lamb intestinal digestive enzymes is not regulated by diet. 190 59

Twenty human colon carcinoma cell lines were studied for their ability to develop some of the characteristics of the normal intestinal epithelium, e.g., epithelial polarity, presence of the actin-binding protein villin, or the occurrence of an enterocytic differentiation either when cultured under standard conditions, as for Caco-2 cells, or when grown in a glucose-free medium, as for HT-29 cells. Except for the regular presence of villin, which can be considered a marker of the colonic origin of the cells, the cell lines of this study could be classified into four types with regard to their differentiation characteristics. In type 1 (only one cell line, i.e., Caco-2) the cells undergo spontaneously an enterocytic differentiation characterized by a polarization of the cell layer with the formation of domes and the presence of an apical brush border the membrane of which is endowed with hydrolases such as sucrase-isomaltase, lactase, amino-peptidase N, dipeptidylpeptidase IV and alkaline phosphatase. In type 2 (three cell lines: HT-29, HCT-EB, and HCT-GEO) the cells are undifferentiated when grown in the presence of glucose but undergo an enterocytic differentiation when grown in the absence of glucose. In type 3 (eight cell lines: HCT-GLY, HCT-FET, HCT-FRI, HCT-CBS, HCT-ALA, Co-115, HRT-18, and SW-1116) the cells are organized into a polarized monolayer with the formation of domes but without any enterocytic differentiation characteristics, whatever the culture conditions. In type 4 (eight cell lines: HCT-116a, HCT-R, HCT-RCA, HCT-Moser, HCT-8R, SW-480, LS-174T, and Vaco-9P) the cells are organized into a multilayer without any feature of epithelial polarity or enterocytic differentiation, whatever the culture conditions.
 ...
PMID:Epithelial polarity, villin expression, and enterocytic differentiation of cultured human colon carcinoma cells: a survey of twenty cell lines. 334 66

A panel of monoclonal antibodies was produced against purified microvillus membranes of human small intestinal enterocytes. By means of these probes three disaccharidases (sucrase-isomaltase, lactase-phlorizin hydrolase, and maltase-glucoamylase) and four peptidases (aminopeptidase N, dipeptidylpeptidase IV, angiotension I-converting enzyme, and p-aminobenzoic acid peptide hydrolase) were successfully identified as individual entities by SDS PAGE and localized in the microvillus border of the enterocytes by immunofluorescence microscopy. The antibodies were used to study the expression of small intestinal hydrolases in the colonic adenocarcinoma cell line Caco 2. This cell line was found to express sucrase-isomaltase, lactase-phlorizin hydrolase, aminopeptidase N, and dipeptidylpeptidase IV, but not the other three enzymes. Pulse-chase studies with [35S]methionine and analysis by subunit-specific monoclonal antibodies revealed that sucrase-isomaltase was synthesized and persisted as a single-chain protein comprising both subunits. Similarly, lactase-phlorizin hydrolase was synthesized as a large precursor about twice the size of the lactase subunits found in the human intestine. Aminopeptidase N and dipeptidylpeptidase IV, known to be dimeric enzymes in most mammals, were synthesized as monomers. Transport from the rough endoplasmic reticulum to the trans-Golgi apparatus was considerably faster for the peptidases than for the disaccharidases, as probed by endoglycosidase H sensitivity. These results suggest that the major disaccharidases share a common biosynthetic mechanism that differs from that for peptidases. Furthermore, the data indicate that the transport of microvillus membrane proteins to and through the Golgi apparatus is a selective process that may be mediated by transport receptors.
 ...
PMID:Expression and intracellular transport of microvillus membrane hydrolases in human intestinal epithelial cells. 389 50

The expression of small intestinal hydrolases associated with the enterocyte brush border membrane was studied in human colon cancers and foetal colons, by means of monoclonal antibodies against human small intestinal sucrase-isomaltase (SI), maltase-glucoamylase (MGA), lactase (L), aminopeptidase N (APN), and dipeptidylpeptidase IV (DPP-IV). The enzymes were visualized by indirect immunofluorescence on cryostat sections of tumors developed in nude mice with 6 human colon carcinoma cell lines (HT-29, Caco-2, SW-480, HRT-18, HCT-8R, and Co-115), of 27 primary colorectal carcinomas from patients, and of human foetal (16 to 20 weeks of gestation) and normal adult small intestines and colons. All 5 monoclonals bound to the brush border of the adult small intestine, but not to that of the adult colon mucosa. Antibodies against SI, APN and DPP-IV also bound to the brush border of the foetal colons, to apical borders in HT-29 and Caco-2 tumors in nude mice, and to brush border-like structures in 7/27 tumors from patients. No binding was observed for MGA and L in either tumors or foetal colons. Binding of anti-SI antibodies to the brush border of the juxta-tumoral mucosal epithelium was observed in 9/11 samples tested. These data indicate that some colon tumors exhibit a typical pattern of enterocytic differentiation which is of foetal type and which involves at least 3 brush border membrane hydrolases. Monoclonal antibodies to small intestinal hydrolases may, therefore, be important tools for identification and characterization of some differentiated colonic tumors.
 ...
PMID:Immunohistological evidence, obtained with monoclonal antibodies, of small intestinal brush border hydrolases in human colon cancers and foetal colons. 638 73

The human colonic adenocarcinoma cell line Caco-2 forms monolayers of differentiated enterocyte-like cells when cultured on permeable supports. After confluency, Caco-2 cells express a number of brush-border enzymes including lactase-phlorizin hydrolase, sucrase-isomaltase and dipeptidylpeptidase IV. We have studied, with particular emphasis on lactase-phlorizin hydrolase, the modulation of biosynthesis of these enzymes by stimulating second messenger systems. Forskolin induced lactase-phlorizin hydrolase synthesis approximately fourfold within 7 h, suppressed sucrase-isomaltase synthesis, and had little effect on dipeptidylpeptidase IV. Dibutyryl-cAMP, 8-bromo-cAMP and vasoactive intestinal peptide also increased lactase-phlorizin hydrolase biosynthesis, indicating c-AMP dependent regulation. The induction of lactase-phlorizin hydrolase biosynthesis could be inhibited by actinomycin D and was preceded by a fourfold increase in lactase-phlorizin hydrolase mRNA levels, suggesting transcriptional control. Phorbol 12-myristate 13-acetate had an inhibitory effect on brush-border enzyme synthesis, in particular on sucrase-isomaltase, and blocked the forskolin-induced biosynthesis of lactase-phlorizin hydrolase. Lactase-phlorizin hydrolase synthesis was also inducible by hydrocortisone, but maximal induction required at least 3 days during which time sucrase-isomaltase synthesis diminished. The results indicate opposite regulation of lactase-phlorizin hydrolase and sucrase-isomaltase via cAMP and corticosteroids, and suggest that the Caco-2 cell line can serve as a model system to study aspects of the humoral regulation of human intestinal brush-border enzymes in cell culture.
 ...
PMID:Induction of lactase biosynthesis in the human intestinal epithelial cell line Caco-2. 750 90

The heterogenous expression of brush border membrane hydrolases by the human enterocyte-like Caco-2 cell line during morphological and functional differentiation in vitro was investigated at the cellular level. Indirect immunofluorescence revealed that the heterogeneous ("mosaic") expression of sucrase-isomaltase, lactase, aminopeptidase N, and alkaline phosphatase was, in fact, transient in nature. The labeling indexes for each hydrolase gradually increased during culture at postconfluence in order to reach a maximum (> or = 90%) after 30 days, concomitant with an upregulation of their respective protein expression levels. In contrast, dipeptidylpeptidase IV labeling remained relatively constant. Backscattered electron imaging analysis in midstage (12 days postconfluence) monolayers demonstrated a lack of correlation between brush border membrane development and expression of each enzyme studied. Moreover, double immunostaining revealed that none of the other four hydrolases correlated directly with sucrase-isomaltase expression. Finally, immunodetection for the proliferation-associated antigen KI-67 revealed a transient mosaic pattern of proliferation which was inversely related to Caco-2 cell differentiation. These data indicate that enterocytic differentiation-related (as well as proliferation-related) gene expression in Caco-2 cells is regulated but uncoordinated at the cellular level, suggesting that an overall control mechanism is lacking.
 ...
PMID:Uncoordinated, transient mosaic patterns of intestinal hydrolase expression in differentiating human enterocytes. 855 68

The development of hydrolase activity in the intestinal brush border membrane is important for the maturation of digestive function in early life. The development and glucocorticoid control of intestinal enzymes were investigated in the mink (Mustela vison), a carnivorous species, in which the intestine matures relatively late in postnatal life. Mink kits (n = 110 from 20 litters) were either not treated or injected intramuscularly for 7 d with saline, adrenocorticotropic hormone [ACTH, 50 micrograms/(kg.d)] or cortisol 21-acetate [synthetic glucocorticoid, 50 mg/(kg.d)]. The kits were killed at 2, 4, 6, 8 or 10 wk of age and the proximal, middle and distal intestine removed for analyses. Lactase activity was maximal at 4 wk and decreased to about 5% of this level during the following 2 wk. Cortisol treatment stimulated total lactase activity at 2 wk (170% that of controls, P < 0.05) and reduced this activity at 4 wk (20% that of controls, P < 0.001). Aminopeptidases N and A underwent their major developmental increases in activity at 4-6 wk and again, enzyme development was stimulated by cortisol. Other enzymes showed either a gradual increase (maltase), a slight decrease (dipeptidylpeptidase IV) or no consistent change (sucrase) in activity with advancing age from 2 to 10 wk, but the activities remained highest in cortisol-treated kits. Treatment with ACTH enhanced the activity of all enzymes at 2 wk but had little effect thereafter. Intestinal hydrolases develop later in the mink and are sensitive to glucocorticoid induction for a longer period in postnatal life than in species such as rats, pigs or humans. The mink is a useful model in studies of the regulatory mechanisms which influence the development of intestinal brush border hydrolases.
 ...
PMID:Intestinal hydrolytic activity in young mink (Mustela vison) develops slowly postnatally and exhibits late sensitivity to glucocorticoids. 881 92

Maturation of the fetal gastrointestinal tract (GIT) is influenced by both luminal stimuli (e.g. swallowed fluid) and hormonal factors (e.g. endogenous cortisol release). The aims of the present study were 1) to investigate GIT growth and maturation during the last 20% of gestation in pigs (term = 114 +/- 2 d), and 2) to investigate the effect of esophageal ligation, to prevent fetal swallowing, at 80% to 91% gestation. In normal fetuses, marked increases occurred during late gestation in body weight (+95%), relative intestinal weight (+79%, g kg(-1) body weight), activity of some digestive enzymes (1.5- to 10-fold), and absorption of glucose and intact proteins (3- to 6-fold). Fetuses with ligated esophagi had lowered body weight (-20%), reduced intestinal weight (-43%), aminopeptidase A activity (-24%), and glucose absorption (-27%), while lactase, sucrase, and dipeptidylpeptidase IV activities were increased (+40-50%), compared with sham-operated fetuses (all p < 0.05). Other parameters of GIT function remained unchanged by esophageal obstruction (absorption of amino acids and immunoglobulin, activity of chymosin, amylase, trypsin, chymotrypsin, maltase, aminopeptidase N -- all expressed per gram GIT tissue). Ligated fetuses had elevated cortisol levels, which is known to stimulate fetal GIT maturation. We conclude that the rapid development of GIT function in late gestation is diminished by esophageal obstruction, mainly due to slower GIT growth and not inhibition of normal functional development of enterocytes.
 ...
PMID:Prenatal development of gastrointestinal function in the pig and the effects of fetal esophageal obstruction. 1219 78


1 2 Next >>