Biological consequences of receptor-mediated endocytosis

For those receptors that do interact with G proteins (such as those that stimulate 

There is recent data to suggest that there may in fact be a biological role for the internalized insulin and EGF receptors (both of which are themselves tyrosine kinases). Thus, microinjection of insulin-occupied insulin receptors into Xenopus oocytes causes the increased phosphorylation of ribosomal protein S6 (a known substrate for the insulin receptor/kinase) [62] and the EGF receptor in endocytic vesicles has been shown to retain its kinase activity [63]. Whether the internalized insulin receptor/kinase or EGF receptor/kinase has a physiological role or not is as yet unknown. Clearly, though, these data suggest that there is much more to be learned about the role of internalized hormone-receptor complexes, especially those where the receptor possesses intrinsic enzymatic activity. 

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