A Di-leucine Motif and an Upstream Serine in the Interleukin-6 (IL-6) Signal Transducer gp130 Mediate Ligand-induced Endocytosis and Down-regulation of the IL-6 Receptor (*)
- From the (1)Institute of Biochemistry, Rheinisch-Westfälische Technische Hochschule Aachen, 52057 Aachen, Germany, the
- (2)Diabetes Branch, NIDDKD, National Institutes of Health, Bethesda, Maryland 20892-1770, and the
- (3)Institute of Pathology, Rheinisch-Westfälische Technische Hochschule Aachen, 52057 Aachen, Germany
- § To whom correspondence should be addressed: Inst. of Biochemistry, RWTH Aachen, Pauwelsstr. 30, 52057 Aachen, Germany. Tel.: 241-8088837; Fax: 241-8888428.
Abstract
The interleukin-6 (IL-6) receptor complex is composed of two different subunits, the IL-6 binding protein (IL-6R, gp80) and the signal transducing component gp130. Our previous studies revealed that the 10-amino acid sequence TQPLLDSEER within the intracellular domain of gp130 is crucial for the efficient internalization of IL-6. Since this sequence contains a putative di-leucine internalization motif, we further analyzed this region by constructing two additional deletions and a series of point mutants. Analyses of these mutants showed that the di-leucine pair (Leu-145 and Leu-146) is essential for ligand internalization, with leucine 145 being less resilient to exchanges. Furthermore, when a chimeric protein (Tac-STQPLL) composed of the Tac antigen fused to the hexapeptide STQPLL of gp130 was studied, we found that this sequence is sufficient to mediate endocytosis and lysosomal targeting of the chimera. Mutational analysis of three serine residues upstream of the di-leucine motif revealed that mutation of serine 139 to an alanine reduces the initial internalization rate by 50%. This finding suggests that a serine phosphorylation may be important for rapid endocytosis.
Footnotes
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↵* This work was supported by grants from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- IL-6
-
interleukin-6
- IL-6R
-
interleukin-6 receptor
- APRF
-
acute phase response factor
- PBS
-
phosphate-buffered saline
- DMEM
-
Dulbecco's modified Eagle's medium
- PAGE
-
polyacrylamide gel electrophoresis
- CI-M6PR
-
cation-independent mannose 6-phosphate receptor.
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- Received August 31, 1995.
- Revision received December 4, 1995.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
