Localized elaboration of IgA in normal and neoplastic murine mammary cell cultures: relationship to fibronectin matrix.

IgA secretion by the lactating mammary gland culminates a complex sequence of biologic events both within the gland and at distant sites. Because of the many extraglandular influences, it is difficult to investigate IgA secretion at the tissue and cellular levels in the intact animal. In this study, with the use of immunohistofluorescence, we have observed elaboration of IgA by primary monolayer cultures of mammary cells from the glands of mid-pregnant mice and from mammary tumors. In cultures of normal cells, IgA appeared first in vesicular structures on the upper surfaces of the monolayers. Vesicular IgA was maximal at day 5 in culture, and at that time, was observed only over mounds (domelike structures) that were covered with fibrillar fibronectin (FN), and eventually developed a subpopulation of fusiform cells. It appears that the IgA observed was secreted in vitro, that normal mammary epithelial cells must form multicellular FN-bearing structures to secrete IgA in culture, and that by mid-pregnancy the murine mammary gland contains all of the lymphoid cells required for IgA secretion. In contrast, primary cultures of mammary tumors displayed minimal amounts of IgA and FN. The small amount of cell-associated IgA that was detected on tumor cultures was not localized to any multicellular structures nor was it associated with FN, but instead appeared as minute, punctate accumulations on individual cells scattered across the epithelioid areas. This finding is consistent with the loss of specialized functions and the increased autonomy typical of malignant cells. The study in cultured cells of a function as specialized as IgA secretion should permit greater understanding of both the process itself and the despecializations that accompany malignancies of secretory epithelia.

Cyclic AMP-dependent control of the rat hepatic glutathione disulfide-sulfhydryl ratio.

The disulfide-sulfhydryl ratio of rat hepatic tissue has been found to vary diurnally lowest in the early morning and highest in the early evening (Isaacs, J. (1976) Fed. Proc. 35, 1472, and Isaacs, J. and Binkley, F. (1977) Biochim. Biophys. Acta 497, 192-204). Intraperitoneal injections of dibutyryl cyclic AMP induces an increase in hepatic glutathione protein mixed disulfides (GSSProt) combined with a corresponding decrease in reduced glutathione (GSH) and protein sulfhydryl (ProtSH). Also, dibutyryl cyclic AMP caused hepatic catalase activity to decrease and to increase hepatic production of peroxide molecules. A decrease in catalase activity directs more of the increased peroxide into the glutathione peroxidase pathway. This leads to increased amounts of oxidized glutathione (GSSG) which ultimately results in increased levels of GSSProt. Therefore cyclic AMP may mediate its effect on the disulfide-sulfhydryl ratio via control over catalase and peroxide generation. Support for this idea is provided by the close temporal correlation between the diurnal variations in cyclic AMP, hepatic catalase, peroxide generation and GSSProt-GSH levels.

Glutathione dependent control of protein disulfide-sulfhydryl content by subcellular fractions of hepatic tissue.

The disulfide-sulfhydryl (SS/SH) ratios of subcellular fractions of rat hepatic tissue were found to vary diurnally with the ratio lowest in the early morning and highest in the early evening. These changes were found in the nuclear, microsomal and cytosol fractions. The primary reaction is the reversible formation of mixed disulfides of glutathione with proteins. This formation is controlled by the activity of thiol transferase and the level of oxidized glutathione (GSSG) as substrate. Several enzymes including mitochondrial and microsomal oxidases, glutathione reductase and peroxidase and glucose-6-phosphate dehydrogenase were found to control the levels of GSSG. An NADPH-dependent microsomal oxidase system, inhibited by GSSG, was found to produce activated oxygen which served as substrate for flutathione peroxidase. Evidence is presented for the concept that the formation of mixed disulfides of proteins with glutathione is a mechanism for maintenance of a disulfide-sulfhydryl ratio such that the integrity of particulate membranes is maintaine during oxidative and reductive stresses on the hepatic cells.

Plasma concentrations of connective tissue compounds: I. the effect of uterine involution.

The information obtained in a prospective study of plasma concentrations of connective tissue components during the third trimester of pregnancy, 4 days, and again at 6 weeks postpartum, suggests that the increased concentrations of plasma protein-hydroxyproline (hypro-protein), free proline, and GAG are associated with increased rate of hydrolysis of extraskeletal connective tissue components.

Brush border particulates of renal tissue.

Particulates containing a large part of the alkaline phosphatase activity of renal tissue were separated from homogenates and from ribosomal preparations by zonal centrifugation. The particles had a high content of phospholipid and cholesterol that was not removed by treatment with I percent deoxycholate. Enzymatic activities concentrated with the particles were the alkaline phosphatase, a peptidase resistant to proteolysis, glucose-6-phosphatase, inorganic pyrophos-phatase, and adenosine triphosphatase. The particles accumulated leucine with no stimulation from soluble factors and with inhibition by other amino acids; the accumulation was stimulated by adenosine triphosphate and was not inhibited by puromycin. The particles appear to be derived from the membranes of the brush borders of tubular cells.