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Endocytosis by the asialoglycoprotein receptor is independent of cytoplasmic serine residues


Geffen, I; Fuhrer, C; Spiess, M (1991). Endocytosis by the asialoglycoprotein receptor is independent of cytoplasmic serine residues. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 88(19):8425-8429.

Abstract

The human asialoglycoprotein (ASGP) receptor, like most other plasma membrane receptors, has previously been shown to be phosphorylated at serine residues within the cytoplasmic domain. Phorbol esters, which activate protein kinase C, cause hyperphosphorylation and down-regulation of the ASGP receptor in HepG2 cells. To test the importance of serine residues for receptor traffic and function, we have mutated all the cytoplasmic serines of the two receptor subunits H1 (at positions 16 and 37) and H2 (at positions 12, 13, and 55) to alanines or glycines. Stable transfected fibroblast cell lines expressing either mutant H1 alone or both mutant subunits together were created and compared to cell lines expressing the respective wild-type proteins. Mutant and wild-type subunits were found to have very similar distributions between the cell surface and intracellular compartments. Constitutive internalization of H1 alone and ligand uptake and degradation by cells expressing both receptor subunits were not affected by the mutations. Cytoplasmic serines and serine phosphorylation are thus not essential for receptor function and intracellular traffic. Analysis of individual serine mutations identified serine-12 of subunit H2 as the major site of phosphorylation in the ASGP receptor.

The human asialoglycoprotein (ASGP) receptor, like most other plasma membrane receptors, has previously been shown to be phosphorylated at serine residues within the cytoplasmic domain. Phorbol esters, which activate protein kinase C, cause hyperphosphorylation and down-regulation of the ASGP receptor in HepG2 cells. To test the importance of serine residues for receptor traffic and function, we have mutated all the cytoplasmic serines of the two receptor subunits H1 (at positions 16 and 37) and H2 (at positions 12, 13, and 55) to alanines or glycines. Stable transfected fibroblast cell lines expressing either mutant H1 alone or both mutant subunits together were created and compared to cell lines expressing the respective wild-type proteins. Mutant and wild-type subunits were found to have very similar distributions between the cell surface and intracellular compartments. Constitutive internalization of H1 alone and ligand uptake and degradation by cells expressing both receptor subunits were not affected by the mutations. Cytoplasmic serines and serine phosphorylation are thus not essential for receptor function and intracellular traffic. Analysis of individual serine mutations identified serine-12 of subunit H2 as the major site of phosphorylation in the ASGP receptor.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Brain Research Institute
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:1 October 1991
Deposited On:11 Feb 2008 12:13
Last Modified:05 Apr 2016 12:12
Publisher:National Academy of Sciences
ISSN:0027-8424
Additional Information:Copyright: National Academy of Sciences USA
Publisher DOI:10.1073/pnas.88.19.8425
Related URLs:http://www.pnas.org/cgi/content/abstract/88/19/8425 (Publisher)
PubMed ID:1924301
Permanent URL: http://doi.org/10.5167/uzh-158

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