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Receptor‐mediated endocytosis and degradation of insulin‐like growth factor I and II in neonatal rat astrocytes
Author(s) -
Auletta M.,
Nielsen F. C.,
Gammeltoft S.
Publication year - 1992
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490310103
Subject(s) - endocytosis , microbiology and biotechnology , insulin , receptor mediated endocytosis , receptor , degradation (telecommunications) , insulin like growth factor , insulin receptor , growth factor , biology , neuroscience , chemistry , endocrinology , biochemistry , insulin resistance , computer science , telecommunications
Receptor‐mediated internalization and degradation of insulin‐like growth factors, IGF‐I and IGF‐II, were studied in primary cultures of neonatal rat astrocytes. Surface‐bound IGF‐II was rapidly internalized and 80% of cell‐associated radioactivity was located intracellularly after 30 min. IGF‐I was internalized at a slower rate, and only 40% of cell‐associated radioactivity was inside the cell utter 30 min. A pulse‐chase experiment demonstrated that 55% and 70% of internalized IGF‐I and IGF‐II, respectively, was degraded to free amino acids after a 3‐hr chase. Lysosomal and protease inhibitors had different effects on the binding, internalization, and processing of IGF‐I and IGF‐II. Inhibition of lysosomal acidification by chloroquine increased the amounts of surface‐bound IGF‐II and intracellular IGF‐I and reduced the degradation of IGF‐I. The chelating agent phenanthroline increased the surface binding of IGF‐I and IGF‐II and internalization of IGF‐II and reduced the degradation of IGF‐I and IGF‐II. Finally, receptor‐bound IGF‐II on the cell surface was decreased with increasing cell density, whereas IGF‐I binding was unaltered. Our data suggest that cell‐surface expression of IGF‐I receptors and IGF‐II receptors is regulated by different mechanisms and that receptor‐bound IGF‐I and IGF‐II are trafficked and processed by different intracellular pathways in neonatal rat astrocytes.