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Abstract
The recent demonstration that a single mammalian receptor protein binds both mannose 6-phosphate (Man-6-P) and insulin-like growth factor II (IGF-II) with high affinity has suggested a multifunctional physiological role for this receptor, possibly including signal transduction. In order to better understand the functions of this receptor, we have investigated the properties of Man-6-P receptors from non-mammalian species. Receptors were affinity-purified from Triton X-100 extracts of total membranes from Xenopus and chicken liver as well as rat placenta using pentamannosyl 6-phosphate-Sepharose. The Man-6-P receptor was adsorbed to the pentamannosyl 6-phosphate-Sepharose and specifically eluted by Man-6-P in all three species, as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining. When the purified receptors from these three species were cross-linked to 125I-IGF-II with disuccinimidyl suberate, only receptors isolated from rat membranes were affinity-labeled. To further evaluate the properties of these Man-6-P receptors, binding of 125I-rat-IGF-II and 125I-chicken Tyr-Gly-Thr-Ala-IGF-II to purified receptors from Xenopus, chicken, and rat was evaluated by polyethylene glycol precipitation. Only the rat Man-6-P receptor exhibited detectable binding of 125I-IGF-II. These data suggest that the emergence of a high affinity IGF-II binding site on the Man-6-P receptor occurred in evolution after the divergence of mammals from other vertebrates. Thus, the biological actions of IGF-II in chickens and frogs appear to be initiated by the type I IGF receptor.
Highlights
The recent demonstration that a single mammalian phosphorylation [9], andcell proliferation [3] and differentiareceptor protein binds both mannose 6-phosphate tion [10]
In orderto better understand the functions of this receptor, we have investigated the properties of Man-6-P receptors from non-mammalian species
The Man-6-P receptor was adsorbed to the pentamannosyl6-phosphate-Sepharose and eluted by Man-6-P in all three diated by a type-I IGF receptor which is structurally very similar to the insulin receptor, a heterotetrameric tyrosine kinase composed of two a and two /3 subunits [1].Another receptor for IGF-11, the type I1 IGF receptor, bears noresemblance to these signaling receptors
Summary
The recent demonstration that a single mammalian phosphorylation [9], andcell proliferation [3] and differentiareceptor protein binds both mannose 6-phosphate tion [10]. Receptors were affinity-purified from Triton X-100extracts of total membranes from Xenopus and chicken liver as well as rat placenta using pentamannosyl 6-phosphate-Sepharose. Properties of these Man-6-P receptors, binding of '"I- receptor, either by analysis of dose-response relationships or rat-IGF-I1 and '261-chicken Tyr-Gly-Thr-Ala-IGF-I1 to purified receptors from Xenopus, chicken, and rat was evaluated by polyethylene glycol precipitation.
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