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Comparison of the effects of hypertonic sucrose and intracellular potassium depletion on growth hormone receptor binding kinetics and down-regulation in IM-9 cells: evidence for a sequential block of receptor--mediated endocytosis.
- Source :
-
Endocrinology [Endocrinology] 1991 Mar; Vol. 128 (3), pp. 1597-602. - Publication Year :
- 1991
-
Abstract
- To better understand the complex kinetics of human GH (hGH) binding to its receptors, we have further investigated, in IM-9 cultured human lymphocytes, the cellular locus corresponding to the slowly dissociating component of hormone binding, and to the homologous down-regulation of hGH receptors. First, we have detailed the biphasic kinetics of dissociation of bound hormone in control cells at 30 C. When the association at 30 C was extended from 0.5 to 3 h, the time required for half-dissociation of the fast component was slightly decreased (from 30 to 15 min) but that of the slow component increased considerably (from 6 h to 30 h). Concomitantly, the size of the slowly dissociating component increased from 50 to 80% of total. This indicates a maturation of bound hormone, from a rapidly to a slowly dissociating pool and, in the latter, an increase in the apparent affinity that may reflect a molecular rearrangement. Next, we have compared the effect of two procedures reported to inhibit receptor-mediated endocytosis at the level of coated pits. As previously reported, depletion of intracellular K+ abolished the slowly dissociating component and the down-regulation of hGH receptors. In contrast, upon incubation with 0.4 M sucrose, which like K+ depletion virtually abrogated hGH internalization, the dissociation kinetics remained non-first order, and the down-regulation of hGH-receptor was only slightly reduced. Thus, these procedures appear to block receptor-mediated endocytosis at two successive compartments of the cell surface. In conclusion, we propose that some conformational change of hGH-receptor at the cell surface (possibly associated with clustering) may considerably slow down their dissociation and may be sufficient for down-regulation.
- Subjects :
- Cell Line
Down-Regulation
Growth Hormone metabolism
Humans
Hypertonic Solutions
Kinetics
Receptors, Somatotropin physiology
Temperature
Time Factors
Endocytosis physiology
Intracellular Membranes metabolism
Lymphocytes metabolism
Potassium Deficiency metabolism
Receptors, Somatotropin metabolism
Sucrose pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 0013-7227
- Volume :
- 128
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Endocrinology
- Publication Type :
- Academic Journal
- Accession number :
- 1999174
- Full Text :
- https://doi.org/10.1210/endo-128-3-1597