Gene expression and receptor binding of insulin-like growth factor-II in pig choroid plexus epithelial cells.
To elucidate the function of insulin-like growth factor-II (IGF-II) in the choroid plexus, the gene expression and receptor binding of IGF-II were studied in isolated epithelial cells from the porcine choroid plexus. The choroid plexus expressed multiple IGF-II transcripts of 1.2, 1.6, 2.4, and 4.4 kb, at levels higher than those found in porcine liver and kidney. These data suggest that IGF-II is synthesized by the choroid plexus. Choroid plexus epithelial cells contained high levels of IGF-I receptors on the cell surface whereas very low levels of receptor binding were found for 125I-IGF-II and 125I-insulin. Solubilization of epithelial cells showed that a large proportion of the IGF-I receptors were present in the detergent-insoluble fraction whereas IGF-II receptors and insulin receptors were concentrated in the detergent-soluble fraction. These results suggest that IGF-I receptors are located in clathrin-coated pits of the plasma membrane whereas IGF-II receptors and insulin receptors are present in endosomal vesicles. The tyrosine kinase activity of the IGF-I receptor beta-subunit was stimulated by IGF-I, IGF-II, and insulin, in order of potency, suggesting that these peptides exert a regulatory function in the choroid plexus epithelium. In conclusion, we propose that the IGF-I receptor tyrosine kinase on the surface of the epithelial cells in the pig choroid plexus mediates effects of IGF-I and IGF-II, whereas IGF-II receptors are down-regulated due to the synthesis and secretion of IGF-II in these cells.
Nilsson
C
C
Department of Medical Cell Research, University of Lund, Sweden.
Blay
P
P
Nielsen
F C
FC
Gammeltoft
S
S
D000345:Affinity Labels; D000818:Animals; D002831:Choroid Plexus / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D015870:Gene Expression; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013552:Swine
D000345:Affinity Labels; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases