Di-leucine-mediated Internalization of Ligand by a Truncated Growth Hormone Receptor Is Independent of the Ubiquitin Conjugation System*
- From the Department of Cell Biology, Faculty of Medicine and Institute of Biomembranes, Utrecht University, 3584 CX Utrecht, The Netherlands and the ‡Departments of Molecular Biology, Pharmacology and Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110
Abstract
The growth hormone receptor (GHR) is a member of the cytokine receptor family. Its function is to mediate cellular responses upon binding of growth hormone. Ligand binding induces dimerization and activation of the GHR. One mechanism by which the GHR is rapidly inactivated involves the ubiquitin conjugation system, a system implicated in the degradation of cytosolic and nuclear proteins. We have shown previously that the ubiquitin-conjugating system mediates internalization of the GHR. Here, we present evidence that in addition to the ubiquitin-dependent endocytosis signal, the cytosolic tail of the GHR contains a di-leucine motif. Upon truncation of the GHR at amino acid residue 349, this di-leucine motif is activated and mediates ubiquitin-independent internalization of the receptor. Di-leucine-mediated GHR internalization requires functional clathrin-coated pits and results in GHR transport to the lysosome. Although the full-length GHR internalizes independent of the di-leucine motif, this motif may function in internalization of GHR isoforms.
Footnotes
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↵* This work was supported by Grants NWO-902-23-188 and NWO-902-68-244 from the Netherlands Organization for Scientific Research, by European Union Network Grant ERBFMRXCT96-0026, and by the National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ To whom correspondence should be addressed: Dept. of Cell Biology, Faculty of Medicine, Institute of Biomembranes, Utrecht University Heidelberglaan 100, AZU H02.314 3584 CX Utrecht, The Netherlands. Tel.: 31-30-2506476; Fax: 31-30-2541797; E-mail: strous{at}med.uu.nl.
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↵1 The abbreviations used are: GHR, growth hormone receptor; CHO, Chinese hamster ovary; PCR, polymerase chain reaction; MEM-α, Eagle’s minimal essential medium; PBS, phosphate-buffered saline.
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- Received February 11, 1998.
- Revision received March 31, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
