Specificity of insulin-like growth factor binding to type-II IGF receptors in rabbit mammary gland and hypophysectomized rat liver (original) (raw)
1987, Biochemical and Biophysical Research Communications
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Insulin-like growth factor II (IGF-IE) shares sequence homology and predicted three-dimensional structure with insulin and IGF-I. IGF-II can bind, therefore, to a limited extent with the receptors for these two other hormones, as well as to a distinct receptor for IGF-ll. Previous studies have been unable to attribute a particular response of IGF-ll through its own receptor. In the present studies, the IGF-ll receptor is shown to mediate the stimulation of glycogen synthesis in human hepatoma cells since: (i) IGF-ll is found to be capable of stimulating a response at concentrations in which it would primarily interact with its own receptor; (ii) the response to IGF-ll was not blocked by monoclonal antibodies which inhibit the responses of cells through the insulin and IGF-I receptors; and (iii) polyclonal antibodies to the IGF-H receptor were found to mimic the ability of IGF-ll to stimulate glycogen synthesis. These results indicate that the IGF-ll receptor mediates a particular biological response-stimulation of glycogen synthesis in hepatoma cells. Furthermore, a monovalent Fab fragment of the polyclonal antibody to the IGF-ll receptor was also shown to stimulate glycogen synthesis in these cells. These data indicate that clustering of the IGF-ll receptor is not required to stimulate a biological response.
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