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A comparison of lactogenic receptors from rat liver and Nb2 rat lymphoma cells by using cross-linking techniques.

ABSTRACT: Lactogenic receptors were analysed with the use of the cross-linking agent disuccinimidyl suberate to attach covalently 125I-labelled ovine prolactin or human growth hormone to binding sites from (1) liver from pregnant rats and (2) the rat-derived Nb2 lymphoma cell line. Analysis by SDS/polyacrylamide-gel electrophoresis of the proteins cross-linked to labelled hormone in rat liver indicated a major specifically-labelled complex with an Mr of 68,000-72,000, when run under reducing or non-reducing conditions. With Nb2 cells a major specifically-labelled complex with an Mr of 97,000-110,000 was identified, but only when electrophoresis was run using reducing conditions. Assuming one hormone molecule (Mr 22,000-24,000) per hormone-receptor complex, then the receptor proteins have an Mr of 44,000-50,000 for rat liver and 73,000-88,000 for the Nb2 cells. For both cell types the receptors were of lactogenic specificity; lactogenic hormones competed for binding whereas somatogenic hormones did not. These studies suggest that the lactogenic receptors in rat liver membranes and Nb2 cells differ in two respects. Firstly, the Mr of the labelled receptor protein in Nb2 cells is greater than that of the corresponding receptor protein in rat liver membranes; secondly, the Nb2 cell receptor appears to exist as a disulphide-linked oligomer whereas the receptor in rat liver membranes does not.

SUBMITTER: Webb CF

PROVIDER: S-EPMC1148835 | biostudies-other | 1988 Feb

REPOSITORIES: biostudies-other

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Project description:BACKGROUND:Exposure of the developing brain to immune mediators, including antibodies, is postulated to increase risk for neurodevelopmental disorders and neurodegenerative disease. It has been suggested that immunoglobulin G-immune complexes (IgG-IC) activate Fc gamma receptors (Fc?R) expressed on neurons to modify signaling events in these cells. However, testing this hypothesis is hindered by a paucity of data regarding neuronal Fc?R expression and function. METHODS:Fc?R transcript expression in the hippocampus, cortex, and cerebellum of neonatal male and female rats was investigated ex vivo and in mixed cultures of primary hippocampal and cortical neurons and astrocytes using quantitative PCR analyses. Expression at the protein level in mixed cultures of primary hippocampal and cortical neurons and astrocytes was determined by immunocytochemistry, western blotting, proteotype analysis, and flow cytometry. The functionality of these receptors was assessed by measuring changes in intracellular calcium levels, Erk phosphorylation, and IgG internalization following stimulation with IgG-immune complexes. RESULTS:FcgrIa, FcgrIIa, FcgrIIb, FcgrIIIa, and Fcgrt transcripts were detectable in the cortex, hippocampus, and cerebellum at postnatal days 1 and 7. These transcripts were also present in primary hippocampal and cortical cell cultures, where their expression was modulated by IFN?. Expression of Fc?RIa, Fc?RIIb, and Fc?RIIIa, but not Fc?RIIa or FcRn proteins, was confirmed in cultured hippocampal and cortical neurons and astrocytes at the single cell level. A subpopulation of these cells co-expressed the activating Fc?RIa and the inhibitory Fc?RIIb. Functional analyses demonstrated that exposure of hippocampal and cortical cell cultures to IgG-IC increases intracellular calcium and Erk phosphorylation and triggers Fc?R-mediated internalization of IgG. CONCLUSIONS:Our data demonstrate that developing neurons and astrocytes in the hippocampus and the cortex express signaling competent Fc?R. These findings suggest that IgG antibodies may influence normal neurodevelopment or function via direct interactions with Fc?R on non-immune cells in the brain.

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A comparison of lactogenic receptors from rat liver and Nb2 rat lymphoma cells by using cross-linking techniques.

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