Polypeptides immunologically related to band 3 are present in nucleated somatic cells.

Band 3, the major transmembrane polypeptide of erythrocytes, mediates the exchange of anions (chloride and bicarbonate) across the membrane. We suspected that band 3 was present on nucleated somatic cells as well as erythrocytes because the senescent cell antigen that is immunologically related to band 3 is present on lymphocytes, platelets, adult liver cells, and embryonic kidney cells; and antibodies prepared against the senescent cell antigen isolated from leukocytes react with erythrocyte band 3. For this reason, we examined human fibroblasts, lung cells, neutrophils, mononuclear leukocytes, squamous epithelial (mouth) cells, lung squamous epithelial carcinoma, mouse neuroblastoma cells, and rat hepatocytes for immunoreactive forms of band 3 by using monospecific antibodies to erythrocyte band 3. The results demonstrated that polypeptides sharing common antigenic determinants with erythrocyte band 3 are present in nucleated somatic cells as determined by immunofluorescence, immunoelectron microscopy, and immunoautoradiography. Peptide mapping revealed substantial sequence homology between erythrocyte band 3 and the band 3-like protein of leukocytes. Immunofluorescence studies indicate that the band 3-like proteins in nucleated cells participate in antibody-induced cell surface capping.

Selenium and mouse mammary tumorigenesis: an investigation of possible mechanisms.

The effects of selenium on 7,12-dimethylbenzanthracene-induced mammary tumorigenesis were examined in C57BL X DBA/2f F1 mice fed a semipurified diet. Mice fed 0.2 ppm selenium developed 56% mammary tumors; in contrast, mice fed 2.0 ppm selenium developed only 16% mammary tumors at 11 months of age. Mice fed the 2.0-ppm selenium diet grew as well as did their counterparts fed the 0.2-ppm selenium diet. In a separate experiment, the level of selenium-dependent glutathione peroxidase was measured in the mammary glands of control and 7,12-dimethylbenzanthracene-treated BALB/c mice fed basal and selenium-supplemented diets. 7,12-Dimethylbenzanthracene treatment resulted in decreased glutathione peroxidase activity n mice fed both low (0.03 ppm)- and high (1.50 ppm)-selenium diets. Thus, the chemopreventive effects of selenium could not be attributed to maintaining high levels of glutathione peroxidase. In a second series of experiments, the effects of selenium were further examined on the growth of mammary cell line YN-4 in monolayer cell culture. The mitochondrial inclusions seen in cells exposed to 5 X 10(-6) M selenium could not be correlated with changes in the activity of the mitochondrial enzymes, cytochrome c oxidase and succinate dehydrogenase, thus implying that there was no demonstratable impairment of mitochondria. The examination of selenium-treated cells with flow cytofluorometry indicated that cells were blocked in S-G2 phases of the cell cycle. This latter result illustrates one feasible approach towards identifying specific mechanisms for the chemopreventive effects of selenium.