Mitogenic and metabolic effects of type I IGF receptor overexpression in insulin receptor-deficient hepatocytes.
We have previously shown that hepatocytes lacking insulin receptors (Ir-/-) fail to mediate metabolic responses, such as stimulation of glycogen synthesis, while retaining the ability to proliferate in response to IGFs. In this study we have asked whether overexpression of type I IGF receptors would rescue the metabolic response of Ir-/- hepatocytes. After IGF-I stimulation, insulin receptor substrate-1 and -2 phosphorylation and PI3K activity were restored to levels similar to or greater than those seen in wild-type cells. Rates of cell proliferation in response to IGF-I increased approximately 2-fold, whereas glycogen synthesis was restored to wild-type levels, but was comparatively smaller than that elicited by overexpression of insulin receptors. In summary, overexpression of IGF-I receptors in Ir-/- hepatocytes normalized insulin receptor substrate-2 phosphorylation and glycogen synthesis to wild-type levels, whereas it increased cell proliferation above wild-type levels. Moreover, stimulation of glycogen synthesis was submaximal compared with the effect of insulin receptor overexpression. We conclude that IGF-I receptors are more efficiently coupled to cell proliferation than insulin receptors, but are less potent than insulin receptors in stimulating glycogen synthesis. The data are consistent with the possibility that there exist intrinsic signaling differences between insulin and IGF-I receptors.
Kim
J J
JJ
Naomi Berrie Diabetes Center and Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Park
B C
BC
Kido
Y
Y
Accili
D
D
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D038362:Glycogen Synthase Kinase 3; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism* / Q000821:virology; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D008938:Mitosis / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011972:Receptor, Insulin / Q000172:deficiency* / Q000235:genetics; D013539:Simian virus 40 / Q000502:physiology; D013002:Somatomedins / Q000502:physiology
D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526298:Irs2 protein, mouse; D010750:Phosphoproteins; D013002:Somatomedins; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3