Role of insulin and insulin-like growth factor receptors in regulation of T84 cell monolayer permeability.
We previously showed that insulin and insulin-like growth factor (IGF)-I and IGF-II caused a dose-dependent increase in permeability through the paracellular pathway of T84 cell monolayers over 3-4 days. Here we have determined which cell surface receptors were involved in this response. Using radioligand binding studies and receptor cross-linking studies, we found that T84 cells possess insulin and IGF-I receptors. There were approximately 20 x 10(3) insulin receptors/cell with a dissociation constant (KD) of 0.5 nM and 29 x 10(3) IGF-I receptors with a KD of 0.6 nM for IGF-I. Cross-linking studies identified the alpha-subunit of insulin and IGF-I receptors with deduced molecular weights of 126 x 10(3) and 128 x 10(3), respectively. IGF-II bound to T84 cells with an apparent KD of approximately 2.0 nM. Radioreceptor cross-linking indicated that IGF-II interacted principally with the IGF-I receptor, although low levels of the IGF-II/mannose 6-phosphate receptor were also expressed on the cell surface. We then correlated the biological effect with the radioligand binding studies. It was first demonstrated that insulin and IGF-I were degraded in medium in the presence of cells. In addition, we showed that continuous exposure for 2-3 days to insulin or IGF-I was required to produce their biological effect on permeability. Taking into account the rate of degradation and the requirement for continuous exposure, we found a close correlation between radioligand binding and the half-maximal effective concentration for the hormonal effects on transepithelial permeability.(ABSTRACT TRUNCATED AT 250 WORDS)
McRoberts
J A
JA
Department of Medicine, Harbor-UCLA Medical Center, Torrance 90502.
Riley
N E
NE
D003106:Colon / Q000166:cytology / Q000378:metabolism*; D003432:Cross-Linking Reagents; D003470:Culture Media; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D010539:Permeability; D011972:Receptor, Insulin / Q000502:physiology*; D017451:Receptors, Somatomedin / Q000502:physiology*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D003432:Cross-Linking Reagents; D003470:Culture Media; D007328:Insulin; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011972:Receptor, Insulin