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

The role of tumor rejection antigens in host antitumor defense mechanisms

BACKGROUND

Normal cells undergo contact inhibition of growth when their surface molecules interact. Tumor cells, however, have undergone a mutation that prevents this arrest of growth upon contact inhibition and allows constant growth. Thus, growth inhibition fails to occur despite the interaction of surface molecules. In recent years a subgroup of these surface molecules has been of interest to cancer investigators. This subgroup has been termed the tumor rejection antigens (TRAs). As the name implies, these are specific to the tumor of origin and may direct the immune system of the host to target the tumor cells and kill them.

METHODS

A literature search was carried out on TRAs to ascertain the current thinking on the subject.

RESULTS

Initial studies of TRAs have revealed that some of them may be heat shock proteins (HSPs). In particular, grp96, a number of the HSP90 family, has been implicated. More recent studies, however, have shown that HSPs alone may not be immunogenic but may act as carrier proteins for tumor specific peptides.

CONCLUSION

Such findings have led to speculation that HSPs or their associated peptides may have a role in the diagnosis and/or treatment of specific cancers. Immunotherapy and bispecific antibodies in particular are areas in which HSPs may prove to be useful.

Characterization of a novel 63 kDa membrane protein. Implications for the organization of the ER-to-Golgi pathway

Owing to the lack of appropriate markers the structural organization of the ER-to-Golgi pathway and the dynamics of its membrane elements have been elusive. To elucidate this organization we have taken a monoclonal antibody (mAb) approach. A mAb against a novel 63 kDa membrane protein (p63) was produced that identifies a large tubular network of smooth membranes in the cytoplasm of primate cells. The distribution of p63 overlaps with the ER-Golgi intermediate compartment, defined by a previously described 53 kDa marker protein (here termed ERGIC-53), as visualized by confocal laser scanning immunofluorescence microscopy and immunoelectron microscopy. The p63 compartment mediates protein transport from the ER to Golgi apparatus, as indicated by partial colocalization of p63 and vesicular stomatitis virus G protein in Vero cells cultured at 15 degrees C. Low temperatures and brefeldin A had little effect on the cellular distribution of p63, suggesting that this novel marker is a stably anchored resident protein of these pre-Golgi membranes. p63 and ERGIC-53 were enriched to a similar degree by the same subcellular fractionation procedure. These findings demonstrate an unanticipated complexity of the ER-Golgi interface and suggest that the ER-Golgi intermediate compartment defined by ERGIC-53 may be part of a greater network of smooth membranes.

Developmental expression of two antigens associated with mouse intestinal crypts

Two monoclonal antibodies were prepared against the duodenal mucosa of four-day-old mice (MIM-1/39 and MIM 1/130). The expression of the antigens was associated with the crypts of the small and large intestine in the fetus and adult. MIM-1/39 was present in epithelial cells of the intervillous areas in the small intestine at 17 and 18 days of gestation; afterwards its expression was detected only in crypt cells from birth to adulthood. Transition from the mouth of the crypts to intestinal villi was abrupt. Expression of MIM-1/39 was first detected at time of birth in the colon: In the adult, only crypt cells expressed the antigen and goblet cells were negative. Antigen MIM-1/130 was detected from 16 to 18 days of gestation in the small intestine, in the mesenchymal matrix lying under the intervillous epithelium. After birth, it was present in the pericryptal mesenchymal matrix. This antigen was also expressed at birth in the colon and remained in the pericryptal matrix in the adult. In vivo, multiple injections of an organic extract of rat amniotic fluid to mothers, starting at 14 days of gestation, induced a profound modulation in the pattern of expression of both antigens at 17 days of gestation: The pattern of expression was comparable to that observed at least 5 days after birth in untreated animals. The expression of both antigens before crypt appearance may reflect some molecular differentiation in preparation for the formation of crypts, while their association with differentiated crypts may indicate that they have a role in the maintenance of crypt functional and/or morphological integrity.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of short-chain fatty acid uptake by apical membrane vesicles of rat distal colon

In this study, the presence of a bicarbonate gradient-dependent, carrier-mediated anion exchange process for butyrate (a representative short-chain fatty acid) uptake in apical membrane vesicles isolated from rat distal colon is described. An outward gradient of both butyrate- and bicarbonate-stimulated [14C]butyrate uptake and resulted in transient accumulation (an "overshoot" phenomenon). Butyrate gradient-stimulated [14C]butyrate uptake was not altered either by an imposed pH gradient or at different pH values. In contrast, bicarbonate gradient-stimulated [14C]butyrate uptake was stimulated severalfold by an additional imposition of an outward pH gradient (pHi = 7.5; pH0 = 6.0). This bicarbonate- and pH gradient-stimulated butyrate uptake was not inhibited by either voltage clamping, with equimolar intravesicular and extravesicular K+ and valinomycin, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an anion-exchange inhibitor. Increasing butyrate concentrations saturated the bicarbonate- and pH gradient-stimulated butyrate uptake with a half-maximal concentration (Km) of 26.9 +/- 1.6 mmol/L. Butyrate uptake was substantially inhibited by 20 mmol/L propionate (45%) and acetate (60%) but was not inhibited by oxalate, inorganic anions (SO4(2-) and NO3-), and transport inhibitors (amiloride, acetazolamide, furosemide, and ouabain). It is concluded from these results that bicarbonate gradient-stimulated butyrate uptake in apical membrane vesicles of rat distal colon occurs via a carrier-mediated anion-exchange process that differs from other DIDS-sensitive anion exchanges [e.g., the Cl- -OH- (HCO3-) process].

The isolated ER-Golgi intermediate compartment exhibits properties that are different from ER and cis-Golgi

A procedure has been established in Vero cells for the isolation of an intermediate compartment involved in protein transport from the ER to the Golgi apparatus. The two-step subcellular fractionation procedure consists of Percoll followed by Metrizamide gradient centrifugation. Using the previously characterized p53 as a marker protein, the average enrichment factor of the intermediate compartment was 41. The purified fraction displayed a unique polypeptide pattern. It was largely separated from the rough ER proteins ribophorin I, ribophorin II, BIP, and protein disulfide isomerase, as well as from the putative cis-Golgi marker N-acetylglucosamine-1-phosphodiester-alpha-N-acetylglucosaminidase, the second of the two enzymes generating the lysosomal targeting signal mannose-6-phosphate. The first enzyme, N-acetylglucosaminylphosphotransferase, for which previous biochemical evidence had suggested both a pre- and a cis-Golgi localization in other cell types, cofractionated with the cis-Golgi rather than the intermediate compartment in Vero cells. The results suggest that the intermediate compartment defined by p53 has unique properties and does not exhibit typical features of rough ER and cis-Golgi.

(Na+ + K+)-ATPase and plasma membrane polarity of intestinal epithelial cells: presence of a brush border antigen in the distal large intestine that is immunologically related to beta subunit

The previously produced monoclonal antibody IEC 1/48 against cultured rat intestinal crypt cells (Quaroni, A., and K. J. Isselbacher. 1981. J. Natl. Cancer Inst. 67:1353-1362) was extensively characterized and found to be directed against the beta subunit of (Na+ + K+)-ATPase as assessed by immunological and enzymatic criteria. Under nondenaturing conditions the antibody precipitated the alpha-beta enzyme complex (98,000 and 48,000 Mr). This probe, together with the monoclonal antibody C 62.4 against the alpha subunit (Kashgarian, M., D. Biemesderfer, M. Caplan, and B. Forbush. 1985. Kidney Int. 28:899-913), was used to localize (Na+ + K+)-ATPase in epithelial cells along the rat intestinal tract by immunofluorescence and immunoelectron microscopy. Both antibodies exclusively labeled the basolateral membrane of small intestine and proximal colon epithelial cells. However, in the distal colon, IEC 1/48, but not C 62.4, also labeled the brush border membrane. The cross-reacting beta-subunit-like antigen on the apical cell pole was tightly associated with isolated brush borders but was apparently devoid of (Na+ + K+)-ATPase activity. Subcellular fractionation of colonocytes in conjunction with limited proteolysis and surface radioiodination of intestinal segments suggested that the cross-reacting antigen in the brush border may be very similar to the beta subunit. The results support the notion that in the small intestine and proximal colon the enzyme subunits are exclusively targeted to the basolateral membrane while in the distal colon nonassembled beta subunit or a beta-subunit-like protein is also transported to the apical cell pole.

Identification, by a monoclonal antibody, of a 53-kD protein associated with a tubulo-vesicular compartment at the cis-side of the Golgi apparatus

Purified Golgi membranes of the human intestinal adenocarcinoma cell line Caco-2 were used as an antigen to produce a monoclonal antibody, G1/93, which specifically labels a tubulovesicular compartment near the cis side of the Golgi apparatus, including the first cis-cisterna itself, as visualized by single and double immunoelectron microscopy with antibodies against galactosyltransferase. The antigen recognized by G1/93 was identified as a protein with a subunit size of 53 kD. Pulse-chase experiments revealed that the 53-kD protein dimerizes immediately after synthesis followed by formation of oligomers of approximately 310 kD, probably homohexamers. The protein has a transmembrane topology with only a short cytoplasmic segment as assessed by protease protection experiments. Glycosidase digestion studies indicated that the protein is probably not glycosylated. The unique subcellular distribution of the G1/93 antigen in close vicinity to the cis-Golgi is in line with the notion that this protein may delineate the biosynthetic transport pathway from the endoplasmic reticulum to the Golgi apparatus. Moreover, G1/93 is a useful marker to identify the cis side of the Golgi apparatus in a variety of human cells.