Xenopus Autosomal Recessive Hypercholesterolemia Protein Couples Lipoprotein Receptors with the AP-2 Complex in Oocytes and Embryos and Is Required for Vitellogenesis

Yi Zhou, Jian Zhang, Mary Lou L King

Research output: Contribution to journalArticle

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Abstract

ARH is required for normal endocytosis of the low density lipoprotein (LDL) receptor in liver and mutations within this gene cause autosomal recessive hypercholesterolemia in humans. xARH is a localized maternal RNA in Xenopus with an unknown function in oogenesis and embryogenesis. Like ARH, xARH contains a highly conserved phosphotyrosine binding domain and a clathrin box. To address the function of xARH, we examined its expression pattern in development and used pull-down experiments to assess interactions between xARH, lipoprotein receptors and proteins in embryo extracts. xARH was detected concentrated at the cell periphery as well as in the perinuclear region of oocytes and embryos. In pull-down experiments, the xARH phosphotyrosine binding domain interacted with the LDL and vitellogenin receptors found in Xenopus oocytes and embryos. Mutations within the receptor internalization signal specifically abolished this interaction. The xARH C-terminal region pulled-down several proteins from embryo extracts including α- and β-adaptins, subunits of the AP-2 endocytic complex. Mutations within either of the two Dφ(F/W) motifs found in xARH abolished binding to α- and β-adaptins. Expression of a dominant negative mutant of xARH missing the clathrin box and one functional Dφ(F/W) motif severely inhibited endocytosis of vitellogenin in cultured oocytes. The data indicate that xARH acts as an adaptor protein linking LDL and vitellogenin receptors directly with the AP-2 complex. In oocytes, we propose that xARH mediates the uptake of lipoproteins from the blood for storage in endosomes and later use in the embryo. Our findings point to an evolutionarily conserved function for ARH in lipoprotein uptake.

Original languageEnglish
Pages (from-to)44584-44592
Number of pages9
JournalJournal of Biological Chemistry
Volume278
Issue number45
DOIs
StatePublished - Nov 7 2003

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Vitellogenesis
Lipoprotein Receptors
LDL Receptors
Oocytes
Clathrin
Phosphotyrosine
Embryonic Structures
Lipoproteins
Vitellogenins
Xenopus
Endocytosis
Proteins
Mutation
Liver
Blood
Genes
Experiments
Oogenesis
RNA
Endosomes

ASJC Scopus subject areas

  • Biochemistry

Cite this

Xenopus Autosomal Recessive Hypercholesterolemia Protein Couples Lipoprotein Receptors with the AP-2 Complex in Oocytes and Embryos and Is Required for Vitellogenesis. / Zhou, Yi; Zhang, Jian; King, Mary Lou L.

In: Journal of Biological Chemistry, Vol. 278, No. 45, 07.11.2003, p. 44584-44592.

Research output: Contribution to journalArticle

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abstract = "ARH is required for normal endocytosis of the low density lipoprotein (LDL) receptor in liver and mutations within this gene cause autosomal recessive hypercholesterolemia in humans. xARH is a localized maternal RNA in Xenopus with an unknown function in oogenesis and embryogenesis. Like ARH, xARH contains a highly conserved phosphotyrosine binding domain and a clathrin box. To address the function of xARH, we examined its expression pattern in development and used pull-down experiments to assess interactions between xARH, lipoprotein receptors and proteins in embryo extracts. xARH was detected concentrated at the cell periphery as well as in the perinuclear region of oocytes and embryos. In pull-down experiments, the xARH phosphotyrosine binding domain interacted with the LDL and vitellogenin receptors found in Xenopus oocytes and embryos. Mutations within the receptor internalization signal specifically abolished this interaction. The xARH C-terminal region pulled-down several proteins from embryo extracts including α- and β-adaptins, subunits of the AP-2 endocytic complex. Mutations within either of the two Dφ(F/W) motifs found in xARH abolished binding to α- and β-adaptins. Expression of a dominant negative mutant of xARH missing the clathrin box and one functional Dφ(F/W) motif severely inhibited endocytosis of vitellogenin in cultured oocytes. The data indicate that xARH acts as an adaptor protein linking LDL and vitellogenin receptors directly with the AP-2 complex. In oocytes, we propose that xARH mediates the uptake of lipoproteins from the blood for storage in endosomes and later use in the embryo. Our findings point to an evolutionarily conserved function for ARH in lipoprotein uptake.",
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