Cation selectivity of gastric H,K-ATPase and Na,K-ATPase chimeras.

Chimeras of the catalytic subunits of the gastric H,K-ATPase and Na, K-ATPase were constructed and expressed in LLC-PK1 cells. The chimeras included the following: (i) a control, H85N (the first 85 residues comprising the cytoplasmic N terminus of Na,K-ATPase replaced by the analogous region of H,K-ATPase); (ii) H85N/H356-519N (the N-terminal half of the cytoplasmic M4-M5 loop also replaced); and (iii) H519N (the entire front half replaced). The latter two replacements confer a decrease in apparent affinity for extracellular K+. The 356-519 domain and, to a greater extent, the H519N replacement confer increased apparent selectivity for protons relative to Na+ at cytoplasmic sites as shown by the persistence of K+ influx when the proton concentration is increased and the Na+ concentration decreased. The pH and K+ dependence of ouabain-inhibitable ATPase of membranes derived from the transfected cells indicate that the H519N and, to a lesser extent, the H356-519N substitution decrease the effectiveness of K+ to compete for protons at putative cytoplasmic H+ activation sites. Notable pH-independent behavior of H85N/H356-519N at low Na+ suggests that as pH is decreased, Na+/K+ exchange is replaced largely by (Na+ + H+)/K+ exchange. With H519N, the pH and Na+ dependence of pump and ATPase activities suggest relatively active H+/K+ exchange even at neutral pH. Overall, this study provides evidence for important roles in cation selectivity for both the N-terminal half of the M4-M5 loop and the adjacent transmembrane helice(s).

Comparison by leukocyte adherence inhibition of human immune response to cancer-associated immunogens, Thomsen-Friedenreich (T) and Tn, myelin basic protein, and organ-specific cancer neoantigens.

Peripheral blood leukocytes from cancer patients exhibit nonadherence to glass as an index of antigen recognition when incubated individually with four distinct, soluble tumor-related substances. Crude cancer extracts, purified antigens, T and Tn, myelin basic protein (MBP), and organ-specific cancer neoantigens (OSN), all elicited narrow dose-dependent leukocyte adherence inhibition (LAI) response curves. The present study focused on the reasons for the narrow antigen dose-LAI response relationship. Between 9 and 20 pmol of antigens elicited the maximum number of nonadherent leukocytes; cleavage products of T antigen and the nonapeptide (T18) of MBP required about a 10-fold increase in molar concentration for the same LAI response. When crude cancer extracts were combined with pure antigen or the pure antigens were combined at concentrations shown to give maximum LAI responses, the positive LAI responses were negated. The chemoattractant LTB4 at 10(-11) M triggered maximum LAI. But when MBP was added with the LTB4 at progressively increasing concentrations, there was dose-dependent negation of LAI. The magnitude of LAI depended on the total amount of mediator released rather than the rate of release. When leukocytes from cancer patients were incubated with optimum to high concentrations of MBP, the supernatants contained a mediator that gave similar bell-shaped dose-LAI responses on control leukocytes indicating that leukocytes from cancer patients react to a much broader range of antigen concentration than indicated by the LAI assay alone. High antigen dose negated LAI because of excess mediator production. Antigen-generated mediators had a biphasic effect inducing nonadherence and then adherence of leukocytes.

Recognition of a purified Mr-40,000 organ-specific immunogen of human lung cancer by class II-restricted T-cells.

An Mr-40,000 polypeptide (p40) was purified from a lung cancer cell line on the basis of its antigenicity with leukocytes from lung cancer patients in an in vitro immunological assay of leukocyte adherence inhibition. Here, the cells and mechanism responsible for recognizing the purified p40 organ-specific cancer neoantigen (OSN) were studied. Buffy coat leukocytes from lung cancer patients showed a bell-shaped dose response with a peak response at 0.75 micrograms/assay. Mononuclear cells showed a similar response pattern, whereas pure T-cells were unreactive. Monoclonal antibodies (MAbs) to T-cell differentiation antigens T3 and T4 inhibited the response in a dose-dependent fashion, whereas anti-T8 had no effect, indicating T helper cells and their T3-antigen receptor complex recognized the antigen. MAbs to class II major histocompatibility complex (MHC) antigens also inhibited the response, whereas MAbs to class I MHC had no effect, indicating an important role for class II MHC antigens of monocytes. None of the MAbs inhibited the response to OSN on membrane fragments, which is mediated by antibody-dependent monocytes. Trypsin- or cyanogen bromide-cleaved p40 OSN triggered a response at the same concentrations as the intact molecule. The p40 OSN incubated with live leukocytes showed less than 30% proteolytic digestion. The results indicate that class II-restricted T-cells recognize, via their antigen-specific cell surface receptors, contiguous sequences within the immunogenic tumor molecule in the context of the molecule or peptides binding to class II transplantation antigens.

Extraction of human organ-specific cancer neoantigens from cancer cells and plasma membranes with 1-butanol.

Immunoprotective tumor antigens of experimental tumors are selectively extracted by 1-butanol. Human organ-specific cancer neoantigens (OSNs) are tumor substances in cancer extracts to which patients with cancer of the same organ respond in the in vitro assay of leukocyte adherence inhibition. Here we determined whether OSNs as measured by leukocyte adherence inhibition assay are also selectively solubilized by 2.5% (v/v) 1-butanol. Butanol extracts of live tissue-cultured human cancer cells as well as extracts of primary breast cancer contained OSNs as determined by leukocyte reactivity in leukocyte adherence inhibition. With two-phase butanol, OSN activity was recovered in the aqueous and not in the organic phase, indicating that OSN is not a lipoprotein. The butanol-soluble OSN, whether allogeneic or autologous, was recognized by the T4 subset of T-cells in association with Class II major histocompatibility complex antigens of monocytes. Autologous OSN was extracted from membrane preparations of autologous primary cancer. Butanol extracts contained the previously identified Mr 40,000 protein OSN. Butanol removed about 50% of the Mr 40,000 protein OSN from live cancer cell membranes. Probably because of residual OSN in the membrane fragments and the ability of OSN to reassociate with the membrane, the T8 subset of pure T-cells responded positively to autologous cancer extracts. Passage of the autologous extract through an anti-Class I major histocompatibility complex antigen affinity column but not through a control affinity column negated the activity of the extract with pure autologous T-cells. The results indicate that human OSNs share with immunoprotective tumor antigens of experimental tumors the unique physicochemical property of being selectively extracted by 2.5% butanol.

Identification of a Mr 40,000 polypeptide from colorectal cancer which expresses organ-specific cancer neoantigen activity as determined by leukocyte adherence inhibition.

Human cancers express organ-specific neoantigens (OSNs) that elicit immune responses in the tumor host. Leukocyte adherence inhibition, an in vitro assay that detects the antitumor immunity, was used to monitor the purification of the OSN from serum-free spent medium of tissue-cultured colon cancer cell lines (HCT-15 and SW-620). A monoclonal antibody (anti-p40) directed to a cross-reactive framework determinant of Mr 40,000 (p40) cell surface polypeptide, which was a principal component of the enriched isolate with OSN activity, was used to monitor the purification of p40 by enzyme-linked immunosorbant assay. About 50 liters of spent medium were generated from 20 m2 of cells, collected, concentrated, and then separated by anion exchange, molecular-sieve, and blue-Sepharose affinity chromatography. OSN and p40 activity coisolated. p40 was then purified by monoclonal antibody anti-p40 affinity chromatography. The affinity-purified fraction was enriched for both p40 and leukocyte adherence inhibition activity that was specific for leukocytes from colon cancer patients in blind leukocyte adherence inhibition assays. When affinity-purified p40 from colon and lung cancers was tested blind in a criss-cross fashion with leukocytes from colon and lung cancer patients, the positive responses were to the appropriate p40. The homologous colon cancer p40 molecule showed size and considerable charge microheterogeneity (pI 6.3 to 7.6). Affinity-purified p40 and OSN coisolated on hydrophobic interaction and hydroxylapatite high-pressure liquid chromatography. Note that not all colon cancer OSN activity was bound by the anti-p40 affinity column. However, unbound OSN activity also eluted from hydrophobic interaction high-pressure liquid chromatography at the same time as affinity-purified p40, and residual p40 activity was detected by enzyme-linked immunosorbant assay. The results indicate that a p40 glycoprotein from the cell membrane of colon cancer cells coisolates with fractions having OSN activity. Impurities do not seem to account for the OSN activity. The OSN epitope on the Mr 40,000 molecule is recognized by leukocytes from colon cancer patients and is distinct from the cross-reactive framework determinant recognized by mouse monoclonal antibody anti-p40.

An isolated enriched organ-specific cancer neoantigen of human lung cancer for leukocyte adherence inhibition assays.

Until now, measurement of human antitumor immunity to organ-specific cancer neoantigen (OSN) by the leukocyte adherence inhibition (LAI) assay depended on using crude extracts of cancer. In this study, a new method is presented to generate and to isolate a highly enriched OSN from spent medium of a lung cancer cell line, NCI-H69, grown in chemically defined medium. Production of large quantities of OSN with minimal contamination by extraneous proteins was possible. Four physicochemical steps were used to give a 1000-fold enrichment of OSN activity: anion-exchange and molecular-sieve chromatography; Blue Sepharose affinity chromatography; and finally anion-exchange high-pressure liquid chromatography. The enriched OSN isolates showed dose-response antigenicity when tested in LAI assay with leukocytes from lung cancer patients but had no antigenicity with leukocytes from control subjects or patients having malignant melanoma, colon cancer, or pancreatic cancer. Cross-reactive antigenicity was observed with leukocytes from patients with breast cancer and slight reactivity with leukocytes from bladder cancer patients. The final isolate from the four-step separation procedure as well as the isolates produced using additional separation techniques consistently had antigenicity at less than 10 ng in blocking LAI and 500 ng in the direct assay and showed components with molecular weights of about 62,000 +/- 3,000 (SD) (p62), 40,000 +/- 3,000 (p40), and 25,000 +/- 1,000 (p25) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The OSN isolates on two-dimensional gels showed p40 to have microheterogeneity (seven spots), with a pl from 6.2 to 7.6, and p62 and p25 as even more basic streaks. The polypeptide bearing the antigenic determinant was not purified, although we tried to separate p62, p40, and p25 to determine whether they carried the OSN determinant. The results of this study are important in showing that an isolate of an organ-specific tumor antigen containing 5 to 13 components, as determined by highly sensitive silver stains and radiolabeled patterns on single and two-dimensional gels, can be used successfully in LAI to measure tumor immune responses.

Purification from a human lung cancer cell line of a water soluble molecule mediating leukocyte adherence inhibition for patients with lung cancer.

Soluble lung tumor activity as determined by LAI2 was enriched by physicochemical methods from chemically - defined spent medium of a lung cancer cell line (NCI-H69). To identify the polypeptide carrying the antigenic determinant, splenic lymphocytes of BALB/c mice were immunized with the enriched isolate and hybridized with mouse plasmacytoma cells. Eight hybrids were cloned successfully and produced MAbs that immunoprecipitated principally a single chain of Mr 40,000 (p40) as well as minor chains of Mr 25,000 (p25) and Mr 13,000 (p13) which were probably degradation products of p40. On 2D gels, p40 was composed of 7 spots with a p1 of 6.3 to 7.6, which was not altered by neuraminidase digestion. Affinity chromatography with MAb anti-p40 absorbed p40 and LAI activity. The bound and recovered fraction was enriched for p40 and LAI activity. Affinity-purified p40 also contained the previously identified p25 and p13 as well as a Mr 32,000 peptide (p32). MAb anti-p40 was directed to a common framework determinant on p40 since MAb anti-p40 bound to cancer cells from other organs. The comparatively lung cancer organ-specific determinant recognized by leukocytes from lung cancer patients was not recognized by the MAb. Affinity-purified p40 triggered LAI for leukocytes from patients with lung cancer but not for leukocytes from control subjects or patients with colon cancer or malignant melanoma in rigorous blind testing. Crossreactivity was observed with leukocytes from patients with breast cancer. LAI activity of affinity-purified p40 seems unlikely to result from an unidentified impurity. Thus a p40 molecule has been purified that is expressed on the membranes of lung cancer cells and triggers immunologically-mediated LAI.

Oxidative metabolism, cytoskeletal system, and calcium entry of leukocytes in the phenomenon of sensitizing cancer extract-induced leukocyte adherence inhibition.

We examined some of the metabolic events that regulate sensitizing cancer extract-induced leukocyte adherence inhibition and found that human leukocytes adhere in a comparatively passive manner to glass in serum-free medium. Adherence of leukocytes to glass did not require oxidative metabolism, microtubules, microfilaments, or calcium entry, whereas leukocyte mobility excited by sensitizing cancer extract did. Calcium antagonists, lanthanum chloride, cromolyn sodium, nifedipine, trifluoperazine, and lidocaine, prevented sensitizing cancer extract-induced leukocyte mobility. Calcium agonist, ionophore A23187, excited leukocyte mobility. Ouabain, which inhibits Na+-K+-adenosine triphosphatase and may increase intracellular Ca2+ as a result, also excited leukocyte mobility. Monocytes, armed with serum from patients with early cancer and challenged with the same sensitizing tumor antigen, generated a leukotriene mediator that excited leukocyte mobility; cromolyn sodium, nifedipine, and trifluoperazine antagonized the synthesis of the mediator. The calcium antagonists inhibited the leukotriene mediator and authentic leukotrienes B4, C4, and D4 from exciting leukocyte mobility. The results showed that leukocyte mobility, excited by sensitizing cancer extract, is an active process depending upon immunologically triggered release of a leukotriené mediator from armed monocytes. Leukocyte adherence inhibition requires many of the same physiological events that chemokinesis and chemotaxis do and is thus an assay to study either immunologically released chemoattractants or chemoattractants themselves on leukocyte locomotion.

Modulation of antigen-induced leukocyte adherence inhibition by metabolites of arachidonic acid and intracellular nucleotides.

After binding a sensitizing tumor antigen, human leukocytes undergo a series of changes that lead to a loss of their glass-adherent properties; a phenomenon called leukocyte adherence inhibition (LAI). After surgery or when patients have a large tumor burden, their test results become negative. This study shows that in vitro incubation of the leukocytes for 5 min with PGE2 converted to positive the negative test, in an immunologically specific manner. The effect was critically dose-dependent, too little or too much did not alter the result. The same effect was achieved with PGE2, PGI2, aminophylline or other drugs that raise intracellular nucleotides, including dibutyryl cyclic AMP and dibutyryl cyclic GMP. Dibutyryl cyclic AMP stimulated a stronger response and 100 times less was needed than of dibutyryl cyclic GMP. Prostaglandins did not mediate LAI since Indomethacin failed to inhibit a positive test. Nonetheless, arachidonate metabolites were critical for the LAI phenomenon since BPB and mepacrine, inhibitors of phospholipase A2, negated the LAI response. Moreover, ETYA, phenidone and NDGA, inhibitors of the lipoxygenase metabolic pathway, all negated the positive LAI response. The positive response was especially sensitive to nullification by ETYA. Although the last-named drugs inhibit other arachidonate metabolic pathways too, conclusive evidence that the metabolites of the lipoxygenase pathway, and leukotrienes in particular, mediate the LAI response was the fact that FPL 55712, a competitive antagonist of SRS, nullified a positive response at levels as low as 10(-13) M. The results imply that prostaglandins were able to modulate the expression of LAI by affecting intracellular nucleotides, but leukotrienes, it seems, were the metabolites that mediated leukocyte nonadherence after monocytes recognized and bound tumor antigen.

Predictive value of tube leukocyte adherence inhibition (LAI) assay for breast, colorectal, stomach and pancreatic cancer.

The tube LAI assay measures accurately antitumor immunity in patients with early cancer but fails to detect up to 75% of patients with advanced cancer due to excess circulating organ-specific neoantigen (OSN). Substances such as prostaglandin E2 (PGE2) or aminophylline, which increase intracellular nucleotides in leukocytes of patients with advanced cancer reversed this nonreactivity and greatly increased the sensitivity of the assay without any loss of specificity. Antitumor immunity can now be detected in advanced cancer, and a combination of the two assays gives prognostic potential to the assay: a positive test with PGE2 and negative test without indicates the patient has a large tumor burden. The specificity of the assay for each cancer was high and in most instances was greater than or equal to 95%. The PGE2 stimulated assay retained the high specificity. The sensitivity of the regular tube assay was often low, 33-56% because of the many advanced cancer patients tested, whereas the PGE2 stimulated assay showed almost a two-fold increase in sensitivity, 67-93%. The diagnostic value of the assay was estimated by calculating the predictive value for different prevalences of cancer. It was found that at low prevalences of cancer as found in the general population, the assay had a low diagnostic value since few patients with a positive test would have the cancer tested for. With prevalences of cancer of 5% or greater as might be found in a tertiary care clinical setting, the assay would seem to have diagnostic value since one half or more patients with a positive test would have the cancer tested for. Most false positives, but not all, are found in patients who have lesions that are often considered to increase their risk for cancer: severe dysplasia of the breast, colon adenomas, chronic atrophic gastritis and chronic pancreatitis, suggesting that the assay predicts oncogenesis.