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C R Kahn

Publications and source records attributed to C R Kahn.

At least 343 records · Page 19Linked to original sources
PubMed1981

Demonstration by radiation inactivation that insulin alters the structure of the insulin receptor in rat liver membranes.

Using the technique of radiation inactivation we have previously shown that the insulin receptor in rat liver membranes is composed of at least two functional components: an insulin binding component and a component which acts as an affinity regulator ((1980) J. Biol. Chem. 255, 3412-3419). In the present study, we have used this technique to examine whether insulin alters the size or structure of the insulin receptor. When insulin is bound to its receptor in liver membranes before radiation, there is a marked change in the inactivation profile. Analysis of the results of indicated that insulin binding to its receptor caused a decrease in the functional size of the insulin binding component from 115,000 to 76,000 and also diminished the interaction between the binding and regulatory components. The magnitude of these effects depended on the insulin concentration, and analogues of insulin with reduced receptor affinity show a reduced effect. Under these conditions, there was no change in the apparent size of the affinity regulator (about 260,000). These data suggest that the interaction of insulin with its receptor in situ produces a change in receptor structure which may be important in signal transmission.

Animals↗
PubMed1981

Short-lived cytoplasmic regulators of gene expression in cell cybrids.

Somatic cell hybridization is a valuable tool for investigation the control of gene expression in eukaryotic cells. Studies of hybrid cells, heterokaryons, reconstructed cells and cybrids (cytoplasmic hybrids) have suggested that cytoplasmic factors may be involved in this regulatory process. Unfortunately, studies of this kind usually require that hybrid or modified cells be maintained for some time in a selective environment during which chromosomal losses or other changes may modify the genetic functions of the cells and thus vitiate conclusions about the mechanism of gene regulation. We report here the preparation of cybrids between enucleated mouse fibroblasts (Cl-1-D) and differentiated rat hepatoma cells (Fao) and the use of a combination of histological techniques to identify these modified cells early after fusion without the use of selective media. We found that albumin production in most cybrids was suppressed (extinguished) at 12-20 h after fusion but was restored by 48 h. These results suggest that there is a cytoplasmic factor in the fibroblast which exerts negative control over expression of the albumin gene, but which in the absence of the fibroblast nucleus, is not renewed and therefore short-lived.

Albumins↗
PubMed1981

Transfer of heritable properties by cell hybridization: specificity and the role of selective pressure.

Enucleated chloramphenicol (CAP) resistant mouse L-cells (LEA-2A) were fused with the mouse hepatoma cells (BW1J). The resultant cybrids expressed CAP resistance (the property used in selection of the cybrids), and also expressed the hepatic-specific functions of the BW1J parent. Hybrids between these same cells, on the other hand, exhibited chloramphenicol resistance and extinction of the hepatoma-specific properties. Cybrids were also prepared between enucleated rat hepatoma cells (FT-2) and mouse erythroleukemia cells (C19TK). The resultant cybrids selected in tyrosine-free medium expressed phenylalanine hydroxylase, an enzyme normally appeared to be the result of activation of the previously silent gene of the C19TK cells. These cybrids, however, did not express any other liver-specific functions present in the FT-2 cytoplast donor. These experiments suggest that the transfer of heritable properties by cell cybridization is selection specific and that activation or extinction observed in hybrids may not occur in cybrids of the same cells.

Animals↗
PubMed1981

Autoantibodies to insulin receptors.

In summary, these studies using antibodies to the insulin receptor have provided some new insights into the structure of the insulin receptor and the action of insulin itself. They suggest that most of insulin's actions are mediated through a common pathway and these can be initiated by interaction of ligands other than insulin with the insulin receptor. These include the entire spectrum of metabolic effects (both acute and chronic). Receptor occupancy alone is not sufficient for signal generation. Both insulin and anti-receptor antibody induce receptor aggregation which appears to be required for activity. And finally, although both insulin and anti-receptor antibody are internalized, there is no evidence to suggest that this is important in their action. The growth effect of insulin appears to be mediated via a different pathway.

Adipose Tissue↗
PubMed1981

Insulin-induced receptor loss in cultured human lymphocytes is due to accelerated receptor degradation.

We have measured the turnover rate of the polypeptide subunits of the insulin receptor in cultured human lymphocytes (IM-9 line) and have investigated the mechanism of insulin-induced receptor loss. To estimate the rate of receptor degradation, lymphocytes were either pulse-labeled with [35S]methionine or surface labeled with Na125I and lactoperoxidase. The insulin receptor was isolated by immunoprecipitation with anti-receptor antibody, and the rate of loss of radioactivity from each receptor subunit was determined after sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Two major (Mr 135,000 and 95,000) and one minor (Mr 210,000) subunits were found. By both labeling methods, the half-lives of the major insulin receptor subunits were 9--12 hr in normal media. When the cells were cultured in media containing 1 microM insulin the turnover was accelerated 2.5- to 3.5-fold (half-life approximately 3 hr). The increase in degradation rate was dependent on the insulin concentration and correlated well with the ability to "down-regulate" the receptor. Guinea pig insulin was about 2% as active as porcine insulin in accelerating degradation, and human growth hormone was without effect. The acceleration of receptor degradation induced by insulin was partially blocked by 100 microM cycloheximide. The rate of biosynthesis of the insulin receptor did not appear to be altered in the presence of 1 microM insulin after correction for the change in degradation rate. In conclusion, these data demonstrate that insulin-induced receptor loss in cultured lymphocytes is due to accelerated receptor degradation.

Animals↗
PubMed1981

Direct demonstration of glycosylation of insulin receptor subunits by biosynthetic and external labeling: evidence for heterogeneity.

Insulin receptors of human lymphocytes (IM-9 line) were biosynthetically labeled with [3H]glucosamine, [3H]galactose, [3H]fucose, or [3H]mannose. After solubilization in Triton X-100, cell extracts were immunoprecipitated with serum from a patient containing autoantibodies to the insulin receptor. Na-DodSO4/polyacrylamide gel electrophoresis of the immunoprecipitates under reducing conditions showed the presence of major labeled subunits of apparent Mr 134,000 and 98,000 and a minor component of Mr 206,000. The ratio of activity in the 134,000 versus 98,000 Mr bands varied from 2:1 for mannose to 1.2:1 for galactose. In addition, the receptor subunits could be demonstrated when the cell surface of intact lymphocytes was labeled with NaB3H4 by using either the galactose oxidase (acts on nonreducing terminal galactose and N-acetylgalactosamine) technique or the periodate (oxidizes sialic acid) technique. With the periodate treatment, NaB3H4 labeled preferentially the Mr 98,000 band. With the galactose oxidase procedure, on the other hand, NaB3H4 labeled only the Mr 134,000 band; prior treatment with neuraminidase increased the labeling of this band and also revealed the Mr 98,000 subunit. These data demonstrate that the major subunits of the insulin receptor are complex glycoproteins that have differences in the nonreducing ends of the carbohydrate chains. In the Mr 134,000 subunit, there appear to be more exposed galactosyl or N-acetylgalactosaminyl (or both) residues, whereas the Mr 98,000 subunit appears to have a higher degree of sialylation. These labeling techniques provide new tools to examine the role of the carbohydrate moiety in insulin receptor function and turnover.

Cells, Cultured↗
PubMed1981

The role of pancreatic venous sampling in the localization of occult insulinomas.

The palpation and enucleation of occult insulinomas (less than 15 mm) can be a difficult surgical problem even with good arteriographic localization. In the authors' limited experience, confirmation of arteriographic findings by pancreatic venous sampling provided little additional localizing information. However, if arteriography is negative or equivocal, venous sampling can indicate the segment of pancreas to be "blindly" resected if the adenoma is not palpable. Venous sampling may be misleading in polyendocrine syndromes because of the frequency of multiple adenomas and variable hormone production.

Adenoma, Islet Cell↗
PubMed1981

Heterogeneity of the insulin-receptor interaction in lipoatropic diabetes.

[125] Insulin binding to its receptors was studied on circulating cells from 11 patients (8 females and 3 males) with lipoatropic diabetes. The patients ranged in age from 9-54 yr. All were insulin resistant, as evidenced by fasting hyperinsulinemia and insulin tolerance tests. Nine patients were evaluated by specific [125] insulin binding to monocytes. Three different patterns of receptor abnormalities were observed: 3 patients demonstrated decreased binding due to decreased binding capacity, 2 patients revealed normal tracer binding with decreased receptor affinity,, and 4 patients had normal or increased insulin binding. [125] Insulin binding to erythrocytes in 9 cases demonstrated similar heterogeneities of initial binding. In most cases there was a good correlation between the binding with erythrocytes and monocytes, although decreased affinity was not observed in the red blood cells. There was no obvious correlations between the nature of the receptor defect and the clinical patterns in these patients. Heterogeneity in insulin binding was even observed among affected members of the same family. Antibodies to the insulin receptor were not detected in any of these patients by either binding inhibition or immunoprecipitation assays. These data suggest that the pathogenesis of the insulin resistance in lipoatropic diabetes is heterogeneous and may involve both receptor and postreceptor abnormalities.

Adolescent↗