Insulin-like growth factor-II receptors in cultured rat hepatocytes: Regulation by cell density

✍ Scribed by Carolyn D. Scott; Robert C. Baxter

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 786 KB
• Volume: 133
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041330314

✦ Synopsis

Insulin-like growth factor-ll (IGF-II) receptors in primary cultures of adult rat hepatocytes were characterized and their regulation by cell density examined.

In hepatocytes cultured at 5 x lo5 cells per 3.8 cm2 plate, ['251]ICF-ll bound to specific, high affinity receptors (Ka = 4.4 + 0.5 x lo9 Ilmol). Less than 1% cross-reactivity by IGF-I and no cross-reactivity by insulin were observed. IGF-I I binding increased when cells were permeabilized with 0.01 % digitonin, suggesting the presence of an intracellular receptor pool. Determined by Scatchard analysis and by polyacrylamide gel electrophoresis after affinity labeling, the higher binding was due solely to an increase in binding sites present on 220 kDa type II ICF receptors. In hepatocytes cultured at low densities, the number of cell surface receptors increased markedly, from 10- 20,000 receptors per cell at a culture density of 6 x lo5 cells/well to 70-80,000 receptors per cell at 0.38 x lo5 cells/well. The increase was not due simply to the exposure of receptors from the intracellular pool, as a density-related increase in receptors was also seen in cells permeabilized with digitonin. There was no evidence that IGF binding proteins, either secreted by hepatocytes or present in fetal calf serum, had any effect on the measurement of receptor concentration or affinity. We conclude that rat hepatocytes in primary culture contain specific ICF-lI receptors and that both cell surface and intracellular receptors are regulated by cell density.

Insulin-like growth factor-I1 (IGF-II) belongs to a family of growth factors with insulin-like structure (Rinderknecht and Humbel, 1978) and actions (Zapf et al., 1978). Although specific receptors for IGF-I1 (type I1 IGF receptors) have been described in a wide variety of tissues and cell types (August et al.