Ultrastructural localization of acid mucosubstances in the mouse colon with iron-containing stains.

Selective ultrastructural staining of acid mucosubstances in sites containing histochemically identifiable sulfo- and sialomucins has been obtained in fixed cryostat sections with both ferric chloride and colloidal iron solutions. The rectosigmoid region of mouse colon was fixed in glutaraldehyde, formalin, or phosphate-buffered osmium tetroxide, and 40 micro cryostat sections of this material were treated with 0.1 to 0.4% ferric chloride or with a solution of dialyzed ferric chloride, ammonia, and glycerin. Specific staining depended upon the pH of the iron-containing solutions, and the optimal value was found to be approximately 2.0. Specific localization of acid mucosubstances has been noted in intracellular sites, including globules within colonic goblet cells and "deep crypt" mucous cells, small vesicles of the superficial nongoblet epithelial cells, and Golgi lamellae within each of these cell types. Extracellular material, presumed to be acid mucosubstance, was found on the surface of the epithelial microvilli and on the lumenal surface of capillary endothelium. Similar material formed a reticular network surrounding stromal cells, collagen bundles, and various colonic connective tissue elements.

A novel marker glycoprotein for the microvillus membrane of surface colonocytes of rat large intestine and its presence in small-intestinal crypt cells.

Murine mAbs were produced against purified microvillus membranes of rat colonocytes in order to establish a marker protein for this membrane. The majority of antibodies binding to the colonic microvillus membrane recognized a single protein with a mean apparent Mr of 120 kD in both proximal and distal colon samples. The antigen is membrane bound as probed by phase-partitioning studies using Triton X-114 and by the sodium carbonate extraction procedure and is extensively glycosylated as assessed by endoglycosidase F digestion. Localization studies in adult rats by light and electron microscopy revealed the microvillus membrane of surface colonocytes as the principal site of the immunoreaction. The antigen was not detectable in kidney or liver by immunoprecipitation but was present in the small intestine, where it was predominantly confined to the apical membrane of crypt cells and much less to the microvillus membrane of differentiated enterocytes. During fetal development, the antigen appears first in the colon at day 15 and 1-2 d later in the small intestine. In both segments, it initially covers the whole luminal surface but an adult-like localization pattern develops soon after birth. The antibodies were also used to develop a radiometric assay for the quantification of the antigen in subcellular fractions of colonocytes in order to assess the validity of a previously developed method for the purification of colonic brush-border membranes (Stieger, B., A. Marxer, and H.P. Hauri. 1986. J. Membr. Biol. 91:19-31.). The results suggest that we have identified a valuable marker glycoprotein for the colonic microvillus membrane, which in adult rats may also serve as a marker for early differentiation of enterocyte progenitor cells in small-intestinal crypt cells.

Expression of simple epithelial type cytokeratins in stratified epithelia as detected by immunolocalization and hybridization in situ.

Multi-layered ("stratified") epithelia differ from one-layered ("simple") polar epithelia by various architectural and functional properties as well as by their cytoskeletal complements, notably a set of cytokeratins characteristic of stratified tissue. The simple epithelial cytokeratins 8 and 18 have so far not been detected in any stratified epithelium. Using specific monoclonal antibodies we have noted, in several but not all samples of stratified epithelia, including esophagus, tongue, exocervix, and vagina, positive immunocytochemical reactions for cytokeratins 8, 18, and 19 which in some regions were selective for the basal cell layer(s) but extended into suprabasal layers in others. In situ hybridization with different probes (riboprobes, synthetic oligonucleotides) for mRNAs of cytokeratin 8 on esophageal epithelium has shown, in extended regions, relatively strong reactivity for cytokeratin 8 mRNA in the basal cell layer. In contrast, probes to cytokeratin 18 have shown much weaker hybridization which, however, was rather evenly spread over basal and suprabasal strata. These results, which emphasize the importance of in situ hybridization in studies of gene expression in complex tissues, show that the genes encoding simple epithelial cytokeratins can be expressed in stratified epithelia. This suggests that continual expression of genes coding for simple epithelial cytokeratins is compatible with the formation of squamous stratified tissues and can occur, at least in basal cell layers, simultaneously with the synthesis of certain stratification-related cytokeratins. We also emphasize differences of expression and immunoreactivity of these cytokeratins between different samples and in different regions of the same stratified epithelium and discuss the results in relation to changes of cytokeratin expression during fetal development of stratified epithelia, in response to environmental factors and during the formation of squamous cell carcinomas.

Biotinated probe containing a long-terminal repeat hybridized to a mouse colon tumor and normal tissue.

The cloned complementary DNA pMCT-1, which contains an intracisternal A particle long-terminal repeat, is more highly expressed in a mouse colon tumor than in the normal mouse colon. In situ hybridization of biotin-substituted pMCT-1 to fixed frozen sections shows that expression of pMCT-1 is seen throughout the tumor and is highly heterogeneous on a cellular basis, while expression is undetectable in any cell in the normal colonic mucosa.

Human chorionic gonadotropin-like substance in nonendocrine tissues of normal subjects.

By means of two assay systems, a beta chain human chorionic gonadotropin radioimmunoassay and a radioreceptor gonadotropin assay, a chorionic gonadotropin-like substance was demonstrated in extracts of liver and colon obtained at autopsy from three patients who died of nonneoplastic disease. In contrast to placental chorionic gonadotropin, colon and liver chorionic gonadotropin was not bound to concanavalin A-Sepharose columns, indicating that this substance possessed little or no carbohydrate. Previous workers demonstrated that desialylated human chorionic gonadotropin possesses little or no bioactivity in vivo but retains full radioreceptor and radioimmunoassay activity in vitro. Our data suggest that the genome responsible for the human chorionic gonadotropin production is not completely suppressed in adult nonendocrine tissues, and that the chorionic gonadotropin produced by colon and liver has little or no bioactivity in vivo because of its low carbohydrate content. Since many normal tissues produce chorionic gonadotropin, bioactivity may be modulated by regulation of carbohydrate content.

Development of anti-human colonic mucin monoclonal antibodies. Characterization of multiple colonic mucin species.

Structural relationships between colonic mucin species were assessed using a library of monoclonal antibodies (MAbs) directed against purified human colonic mucin (HCM). After immunization of mice with purified mucin from normal human colonic mucosa, 14% of 1,920 fusion products screened were positive for anti-HCM activity in a solid-phase assay. Patterns of selective binding by hybridomas to six discrete HCM species (I-VI) separated by DEAE-cellulose chromatography suggested the presence of both shared and species-specific antigenic determinants among HCM species I-VI. 23 anti-HCMs MAbs (7 IgM, 7 IgG1, and 9 IgG2) demonstrating a range of anti-HCM species specificities, were produced and used to study structural relationships between mucin species. Binding of various mucin species by individual anti-HCM MAbs was shown by competitive solid-phase radioimmunoassay to reflect the presence of identical epitopes on the different species. Adsorption of HCM species on a variety of affinity resins prepared with anti-HCM MAbs demonstrated that binding to multiple mucin species by a single MAb was related to intrinsic structural determinants. Four anti-HCM MAbs recognized protease-sensitive antigenic structures, which suggests that they may be directed to core HCM proteins. 12 of the anti-HCM MAbs were shown by solid-phase assay to recognize either complete (n = 5) or partial (n = 7) isolated colonic mucin oligosaccharide side chains of defined structure. Collectively, these data show the presence of both shared and unique antigenic structural determinants among colonic mucin species. Chromatographic heterogeneity of mucin glycoproteins seems to be related to the existence of biologically significant subclasses in the normal human colon.

Posttranslational processing of secretory component in the rat jejunum by a brush border metalloprotease.

Secretory component (SC) is a glycoprotein that mediates the transcellular transport of polymeric immunoglobulins into external secretions. SC is synthesized and inserted into the plasma membrane of epithelial cells and hepatocytes as a transmembrane protein, where it serves as a receptor for polymeric immunoglobulins. SC is posttranslationally cleaved to a soluble protein before secretion into external fluids. In the rat jejunum, we observed that the molecular weights of both the major membrane and soluble forms of SC were 10,000-20,000 smaller than the comparable hepatic forms of the glycoprotein. We therefore set out to determine the reason for the differences in size of SC between these two tissues. The smaller size of jejunal SC was not due to the action of pancreatic proteases or differential glycosylation but was due to proteolysis by a jejunal brush border protease. The protease was characterized as a metalloprotease, with a pH optimum of approximately 5. It is present in jejunal, ileal, and renal tubular brush borders as an integral membrane constituent. When the protease was inhibited in vivo, conversion of jejunal secretory component to the smaller size was partially prevented. Thus, in the rat jejunum, SC undergoes two posttranslational proteolytic events: conversion of membrane secretory component to the soluble form and conversion of soluble SC to a smaller size by a previously undescribed brush border protease.

Composition of human colonic mucin. Selective alteration in inflammatory bowel disease.

Human colonic mucin has been isolated from mucosal scrapings of fresh surgical specimens of normal controls as well as patients with Crohn's colitis and ulcerative colitis. Following sonication and ultracentrifugation, mucin fractions were separated from other soluble colonic glycoproteins by Sepharose 4B chromatography. After nuclease digestion, cesium chloride gradient centrifugation of the excluded material yielded colonic mucin with an average buoyant density of 1.52 g/ml. Subsequent chromatography of the apparently homogeneous colonic mucin on DEAE-cellulose revealed the presence of at least six distinct mucin species (mucin I-VI). Each mucin species was found to have a distinctive hexose, hexosamine, sialic acid, and sulfate content as well as blood group substance activities. Mucin from five patients with Crohn's colitis was found to represent a mixture of at least six discrete species comparable to those isolated from normal colonic specimens. However, in mucin from eight patients with ulcerative colitis there was a marked and selective reduction of one component mucin subclass, designated species IV. Normal mucin and mucin from patients with Crohn's disease contained 48 +/- 17 and 42 +/- 12 mg of species IV/g, while mucin from patients with ulcerative colitis had 5 +/- 3 mg/g solubilized glycoprotein. The selective absence of species IV was found in preparations from both sigmoid (n = 7) and ascending (n = 4) colon and could not be accounted for by an overall decrease in total mucin content. The selective reduction of species IV was also found in mucin isolated from relatively noninflamed colonic mucosa of patients with ulcerative colitis. The carbohydrate composition and blood group activities of the remaining five mucin species were similar to their normal counterparts. Based on the results to date, there appears to be an underlying selective decrease of one colonic mucin subclass in ulcerative colitis.

Rat and human colonic mucins bind to and inhibit adherence lectin of Entamoeba histolytica.

Establishment of adherence by Entamoeba histolytica is mediated by a 170-kD Gal/GalNAc inhibitable lectin and is required for cytolysis and phagocytosis of mammalian target cells. We studied the biochemical mechanisms of the in vitro interaction between rat and human colonic mucins and axenic E. histolytica trophozoites. Crude mucus prevented amebic adherence to Chinese hamster ovary (CHO) cells by up to 70%. Purification of the colonic mucins by Sepharose 4B chromatography, nuclease digestion, and cesium chloride gradient centrifugation resulted in a 1,000-fold enrichment of the inhibitory mucins. Purified rat mucin inhibited amebic adherence to and cytolysis of homologous rat colonic epithelial cells. Oxidation and enzymatic cleavage of rat mucin Gal and GalNAc residues completely abrogated mucin inhibition of amebic adherence. The binding of rat 125I-mucin to amebae was galactose specific, saturable, reversible, and pH dependent. A monoclonal antibody specific for the 170-kD amebic Gal/GalNAc lectin completely inhibited the binding of rat 125I-mucin. Rat mucin bound to Affigel affinity purified the amebic lectin from conditioned medium. Colonic mucin glycoproteins act as an important host defense by binding to the parasite's adherence lectin, thus preventing amebic attachment to and cytolysis of host epithelial cells.

The mouse carbonic anhydrase I gene contains two tissue-specific promoters.

We report the isolation and characterization of the mouse carbonic anhydrase I (CAI) gene. Direct RNA sequence analysis of the 5' nontranslated regions of CAI mRNA from mouse colon and mouse erythroleukemia cells demonstrated tissue specificity in the lengths and sequences of CAI transcripts. Analysis of several mouse CAI genomic clones showed that the transcripts arose from a single CAI gene with two tissue-specific promoters and eight exons. CAI transcripts in the colon were found to initiate just upstream of the erythroid exon 2 of the CAI gene region sequence. Erythroid transcripts originated from a novel promoter upstream of exon 1, which was located more than 10 but less than 250 kilobases upstream of exon 2. Erythroid exon 1 contained only a nontranslated sequence, which was spliced to exon 2 via a cryptic splice acceptor site located in the region that encoded the colon mRNA 5' nontranslated sequence. The remaining exon-intron junctions were conserved in comparison with those of the CAII and CAIII genes.

Regional differences in normal and cancer-associated glycoconjugates of the human colon.

Because inherent regional differences in colonic epithelium may determine the biologic behavior of tumors originating from different sites, and inasmuch as colonic epithelial cells secrete mucins that may reflect the state of cell differentiation, colonic goblet cell mucin was analyzed with the use of fluorescein isothiocyanate-conjugated lectins and fluorescence microscopy in normal fetal and adult mucosa and in cancers of the proximal and distal colon. In the adult proximal colon only the goblet cell mucin in the upper portion of the crypts was specifically labeled by the lectin Dolichos biflorus agglutinin (DBA), whereas this gradient was progressively lost distally; mucin in the upper and lower crypts of the sigmoid colon and rectum bound the label uniformly. In fetuses less than 22 weeks of age, DBA bound only to mucin in the crypts of the distal colon. Seven of 12 (58%) cancers originating from the proximal colon bound DBA, whereas only 2 of 23 (9%) from the distal colon bound this lectin (P less than .005). Logistic regression analysis suggested that this difference may reflect the occurrence of larger tumors in the proximal colon. Regional differences in the binding of Ulex europaeus agglutinin (UEA-I) to nonneoplastic mucosa was similar to that found by others; predominant binding occurred in the proximal colon in the adult. No difference was noted for UEA-I binding to tumors of the proximal (8 of 12; 66.6%) versus distal (11 of 23; 48%) colon (P = .48). These findings may reflect regional differences in normal and tumor-related carbohydrate structures in mucin of the human colon.

Immunoperoxidase localization of carcinoembryonic antigen in normal human intestinal mucosa.

The indirect, labeled antibody and peroxidase-antiperoxidase complex (PAP) methods were studied to determine their sensitivity in detecting carcinoembryonic antigen (CEA) in conventionally processed specimens of morphologically normal human colon mucosa. CEA-positive staining was demonstrated in 13 of 19 specimens reacted with the PAP method, whereas only 4 of these specimens stained positive with the labeled antibody procedure. Detection of CEA with either technique was unrelated to normal mucosa content of antigen as determined by radioimmunoassay. Tissue fixation in 95% ethanol 1% acetic acid (EA) resulted in an enhanced and defined cytoplasmic staining of the normal colon cell lining the mucosal surface and upper levels of the glandular crypts. Cytoplasmic localization in Formalin-fixed specimens was absent or markedly reduced. Colon goblet cells and the small intestinal epithelium were CEA-negative in both Formalin- and EA-fixed specimens. These results show that the PAP immunoperoxidase method is more sensitive than the indirect, labeled antibody procedure in detecting CEA in morphologically normal colon mucosa. Furthermore, staining of tissues fixed in EA demonstrated that CEA is a product of the columnar epithelial cell and is not associated with goblet cells.

Expression of laminin receptor in normal and carcinomatous human tissues as defined by a monoclonal antibody.

It has been hypothesized that epithelial and endothelial cells interact with the laminin component of basement membranes via a cell surface laminin receptor molecule. It has also been proposed that the expression of this molecule may be involved in the invasion of carcinoma cells from their tissue of origin and their subsequent penetration through blood vessel basement membranes. We report here the use of a monoclonal antibody, LR-3, to define the expression of laminin receptor in normal, dysplastic, and carcinomatous human tissues. Monoclonal antibody LR-3 is shown by immunoblotting to recognize the Mr 67,000 laminin receptor protein, to bind to the carcinoma cells, and to constitute approximately 0.1% of total cellular protein. Numerous normal human epithelial and endothelial cell types, as well as pulmonary macrophages, are shown to express laminin receptor to varying degrees. Selected human mammary carcinomas and colon carcinomas are shown to bind more monoclonal antibody LR-3 than normal or dysplastic counterparts. A monoclonal antibody to laminin receptor now makes possible the study of the role of laminin receptor in tumor cell metastases and in the differentiation and function of various normal human epithelial and endothelial cell types.

Premalignant alterations in the glycosphingolipid composition of colonic epithelial cells of rats treated with 1,2-dimethylhydrazine.

1,2-Dimethylhydrazine is a procarcinogen with selectivity for the colon. In weekly s.c. doses of 20 mg/kg of body weight, this agent produces colonic tumors in virtually 100% of rodents, with a latency period of approximately 6 months. To determine whether alterations in the glycosphingolipid content and composition of rat colonic epithelial cells existed before the development of dimethylhydrazine-induced colon cancer, rats were given s.c. injections of this agent (20 mg/kg body weight per week) or diluent for 5 weeks. Animals were sacrificed at this time period and colonocytes isolated from each group. Glycosphingolipids were then extracted from these cells and analyzed by thin-layer chromatography, high-performance liquid chromatography and gas-liquid chromatography. The results of these studies demonstrate that: (a) the content and relative percentages of globotriaosylceramide is increased, whereas hematoside and globotetraosylceramide are decreased in dimethylhydrazine-treated colonocytes compared to their control counterparts; and (b) differences in the enzymatic activities responsible for the biosynthesis of these glycosphingolipids appear to explain, at least partially, these compositional differences. The present data, therefore, suggest that alterations in certain glycosphingolipids may be an early event in colonic malignant transformation and, furthermore, that these alterations may prove useful in the detection of early colon cancer.

Plasminogen activators and tumor development in the human colon: activity levels in normal mucosa, adenomatous polyps, and adenocarcinomas.

Malignant changes are often accompanied by alterations in activity and composition of the plasminogen activators (PA). To study the relationship between PA expression and the development of colorectal cancer, we determined urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA) activity in normal mucosa (n = 80), adenomatous polyps (n = 76), and adenocarcinomas (n = 71) of the colon. Tissues obtained from surgical resection or polypectomy were analyzed for t-PA and u-PA activity in a specific enzymatic assay using plasminogen, a chromogenic substrate, and selective quenching with monospecific antibodies to both activators. The plasminogen activator activities were found to be changed in adenocarcinomas as compared to normal mucosa. The relative contribution of u-PA (expressed as percentage of u-PA) was raised from 6 to 50% for, respectively, normal mucosa and adenocarcinoma. This change could be attributed to a 3-fold decrease in t-PA activity and a 5-fold increase in u-PA activity in the carcinomas. Adenomatous polyps as a group showed percentages of u-PA [20.2 +/- 1.3 (SE)] which were intermediate as well as significantly different (P less than 0.001) from those of normal mucosa and adenocarcinomas. This observation was strengthened by a gradual rise in the relative contribution of u-PA in four resection specimens containing both adenomatous polyps and adenocarcinomas. Zymography showed the presence of minor quantities of PA-PA inhibitor complexes in the tissue extracts studied. The present study shows that the sequence of normal mucosa-adenomatous polyp-adenocarcinoma in the colon is associated with a parallel change in plasminogen activator activity. Thus, change in the regulation of plasminogen activator activity is an early event in the development of colorectal cancer.

Effect of dietary eicosapentaenoic acid on azoxymethane-induced colon carcinogenesis in rats.

The effects of eicosapentaenoic acid (EPA, n-3 polyunsaturated fatty acid) and linoleic acid (n-6 polyunsaturated fatty acid) on azoxymethane-induced colon carcinogenesis in rats were studied. Male Donryu rats were given two types of semipurified diet containing 4.7% EPA plus 0.3% linoleic acid and 5% linoleic acid. The rats were given s.c. injection of azoxymethane (7.4 mg/kg body weight once a week for 11 weeks) and sacrificed 15 weeks after the last injection of azoxymethane. The tumor incidence and tumor yields (tumors per rat) of the colon were significantly lower in rats on the EPA diet compared to those on the linoleic acid diet; i.e., 33%, 0.41 +/- 0.61 and 69%, 1.66 +/- 1.69, respectively. In the analysis of phospholipid fatty acid composition, the colon tumor showed higher levels of arachidonic acid and lower levels of linoleic acid than those in the normal colon mucosa in both diet groups. Despite the increase of arachidonic acid in colon tumor, the EPA diet suppressed the excessive production of prostaglandin E2, which may be accompanied with neoplastic formation, whereas linoleic acid diet caused a marked increase in the tumor content of prostaglandin E2 compared to normal colon mucosa. These results suggest that EPA exerts its inhibitory effect on colon carcinogenesis by modulating lipid metabolism and inhibiting prostaglandin E2 synthesis in tumor cells.

Distribution of mono-, di, and tri-O-acetylated sialic acids in normal and neoplastic colon.

The purpose of this study was to compare the expression of O-acetylated sialic acids on normal colonic epithelial cells to that on primary and metastatic human adenocarcinoma of the colon and rectum. In 24 cases, the relative percentages of biosynthetically labeled non-, mono-, di-, and tri-O-acetylated sialic acids were measured after hydrolytic release, separation, and identification by paper chromatography. In one case, the presence of di- and tri-O-acetylated sialic acids was confirmed by fast atom bombardment-mass spectral analysis. Differences were observed in the expression of sialic acids between normal colonic epithelium, "uninvolved" colon mucosa remote to a colonic adenocarcinoma, and colonic adenocarcinoma. The levels of mono- and tri-O-acetylated sialic acids accounted for the difference in the ratios of sialic acids expressed between normal and "uninvolved" colonic mucosa, while the total amount of O-acetylation was unchanged. However, no difference was observed in the relative amounts of non- and O-acetylated sialic acids between either fresh and tissue culture-established colon carcinomas, or fresh and tissue culture-established liver metastasis derived from carcinoma of the colon. The relative expression of these O-acetylated sialic acids molecules appears to vary according to tissue type. This study suggests that individuals with adenocarcinoma of the colon express a field defect resulting in abnormal ratios of O-acetylated sialic acids.

Cell surface glycopeptides from human intestinal epithelial cell lines derived from normal colon and colon adenocarcinomas.

The cell surface glycopeptides from an epithelial cell line (CCL 239) derived from normal human colon were compared with those from three cell lines (HCT-8R, HCT-15, and CaCo-2) derived independently from human colonic adenocarcinomas. Cells were incubated with D-[2-3H]mannose or L-[5,6-3H]fucose for 24 h and treated with trypsin to release cell surface components which were then digested exhaustively with Pronase and fractionated on Bio-Gel P-6 before and after treatment with endo-beta-N-acetylglucosaminidase H. The most noticeable difference between the labeled glycopeptides from the tumor and CCL 239 cells was the presence in the former of an endo-beta-N-acetylglucosaminidase H-resistant high molecular weight glycopeptide fraction which was eluted in the void volume of Bio-Gel P-6. This fraction was obtained with both labeled mannose and fucose as precursors. However, acid hydrolysis of this fraction obtained after incubation with [2-3H]mannose revealed that as much as 60-90% of the radioactivity was recovered as fucose. Analysis of the total glycopeptides (cell surface and cell pellet) obtained after incubation with [2-3H]mannose showed that from 40-45% of the radioactivity in the tumor cells and less than 10% of the radioactivity in the CCL 239 cells was recovered as fucose. After incubation of the HCT-8R cells with D-[1,6-3H]glucosamine and L-[1-14C]fucose, strong acid hydrolysis of the labeled glycopeptide fraction excluded from Bio-Gel P-6 produced 3H-labeled N-acetylglucosamine and N-acetylgalactosamine. This high molecular weight glycopeptide fraction was susceptible to mild alkaline borohydride reduction, yielding a mixture of labeled oligosaccharides which contained N-acetylgalactosaminitol. Thus, the HCT-8R cells are expressing fucosylated mucin-type glycoproteins on their surface.

Molecular cloning and characterization of a human adenocarcinoma/epithelial cell surface antigen complementary DNA.

A human adenocarcinoma-associated antigen (KSA) defined by the monoclonal antibody KS1/4 has become the focus of several site-directed strategies for tumor therapy. KSA, a 40,000 Da cell surface glycoprotein antigen, is found at a high density in all adenocarcinomas examined to date and in corresponding normal epithelial tissues. Here we describe the cloning and sequencing of overlapping complementary DNA clones which encode the entire KSA as expressed in UCLA-P3, a human lung adenocarcinoma cell line. We have deduced the 314-amino acid sequence and have compared it to the N-terminal amino acid sequence data of the affinity-purified antigen. The KSA is synthesized as a 314-residue-long preproprotein that is then processed to a 232-residue-long antigen. KSA appears to have a single transmembrane domain of 23 residues that separates the highly charged 26-residue cytoplasmic domain from the extracellular domain. The N-terminal region of the propeptide is rich in cysteines and contains three potential N-glycosylation sites. Computer-assisted analyses at both the DNA and protein levels have found no significant similarities of this protein to known sequences, but a GC-rich 5' terminus is evident. Northern blot analysis shows that transcription of KSA can be detected in RNA isolated from normal colon but not in RNA isolated from normal lung, prostate, or liver.

Effect of different levels of omega-3 and omega-6 fatty acids on azoxymethane-induced colon carcinogenesis in F344 rats.

The effect of various levels of dietary Menhaden fish oil containing omega-3 fatty acids plus corn oil containing omega-6 fatty acids fed during the postinitiation phase of colon carcinogenesis was studied in male F344 rats. Starting at 5 weeks of age, groups of animals were fed the 5% corn oil (5% CO) diet. At 7 weeks of age, all animals except the vehicle-treated controls were administered s.c. injections of azoxymethane (15 mg/kg body wt/week for 2 weeks). 4 days after carcinogen or vehicle treatment, groups of animals were transferred to experimental diets containing 4% Menhaden oil + 1% corn oil (4% MO + 1% CO), 23.5% corn oil (23.5% CO), 17.6% corn oil + 5.9% Menhaden oil (17.6% CO + 5.9% MO), 11.8% corn oil + 11.8% Menhaden oil (11.8% CO + 11.8% MO), or 5.9% corn oil + 17.6% Menhaden oil (5.9% CO + 17.6% MO) and fed these diets until termination of the experiment at Week 38 after carcinogen treatment. An additional group consuming a 5% CO diet was continued on these diets. Colon mucosal ornithine decarboxylase activity and microsomal fatty acid composition of colon mucosa were measured in vehicle-treated animals fed experimental diets for 14 weeks. Fatty acids were also analyzed in the microsomal fraction of colon tumors at termination of the experiment. The body weights of animals fed various experimental diets were comparable. Feeding of high fat diets containing 17.6% CO + 5.9% MO, 11.8% CO + 11.8% MO, or 5.9% CO + 17.6% MO significantly inhibited the incidence (percentage of animals with tumors) of colon adenocarcinomas compared to that of 23.5% CO diet. However, the multiplicity (number of tumors/rat) of colon adenocarcinomas was significantly inhibited only in groups fed the 5.9% CO + 17.6% MO compared to those fed the 23.5% CO diet. The incidence and multiplicity of adenocarcinomas were greater in animals fed the 23.5% CO diet compared to those fed the 5% CO diet. Colonic mucosal ornithine decarboxylase activity was lower in animals fed the 11.8% CO + 11.8% MO, 5.9% CO + 17.6% MO, 5% CO, and 4% MO + 1% CO diets compared to the levels in animals fed the 23.5% CO diet. The increasing levels of Menhaden oil in the diet significantly increased the omega-3 fatty acids such as eicosapentaenoic acid and docosahexaenoic acid and decreased the omega-6 fatty acids such as linoleic acid, linolenic acid, and arachidonic acid in microsomal fractions from colonic mucosa and tumors.