Differential Activation of Acute Phase Response Factor/STAT3 and STAT1 via the Cytoplasmic Domain of the Interleukin 6 Signal Transducer gp130

doi:10.1074/jbc.271.22.12991

Differential Activation of Acute Phase Response Factor/STAT3 and STAT1 via the Cytoplasmic Domain of the Interleukin 6 Signal Transducer gp130

I. DEFINITION OF A NOVEL PHOSPHOTYROSINE MOTIF MEDIATING STAT1 ACTIVATION*

From the ^‡Institute of Biochemistry, Rheinisch-Westfälische Technische Hochschule Aachen, 52057 Aachen, Germany and the
^§Institute of Medical Immunology, Universitätsklinikum Charité, 10098 Berlin, Germany

^¶To whom correspondence should be addressed:
Institute of Biochemistry, RWTH Aachen, Pauwelsstr. 30, 52057 Aachen, Germany.
Tel: 49-241-808-8837; Fax: 49-241-888-8428.

Abstract

Interleukin-6 (IL-6) and γ-interferon (IFNγ) activate an overlapping set of genes via the Jak/STAT pathway. However, at least in human cells, a differential activation of STAT transcription factors was observed: IL-6 activates both acute phase response factor (APRF)/STAT3 and STAT1, whereas IFNγ leads only to STAT1 activation. All STATs cloned so far contain SH2 domains. Since all cytokine receptors using the Jak/STAT pathway were found to be tyrosine-phosphorylated after ligand binding, it has been proposed that specific phosphotyrosine modules within the cytoplasmic domain of the receptor chains recruit different STAT factors. We have analyzed by mutational studies and by phosphopeptide competition assays which of the tyrosine modules of the IL-6 signal transducer gp130 are capable of recruiting either APRF or STAT1. We found that two of the four tyrosine modules that are important for APRF activation also activate STAT1. For these modules, we propose the new consensus sequence YXPQ. We further present evidence that STAT1 is activated independently from APRF suggesting that gp130 contains multiple independent STAT binding sites. We compare the APRF and STAT1 activation motifs of gp130 with the STAT1 activation motif of the IFNγ receptor and demonstrate that the specificity of activation can be changed from APRF to STAT1 and vice versa by only two point mutations within a tyrosine module. These data strongly support the concept that the activation of a specific STAT is determined mainly by the phosphotyrosine module. The significance of these findings for other receptor systems is discussed.

Footnotes

↵* This work was supported by grants from the Deutsche Forschungsgemeinschaft (Bonn, Germany) and the Fonds der Chemischen Industrie (Frankfurt/Main, Germany). 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.

This work is dedicated to Prof. Dr. W. Gerok on the occasion of his 70th birthday.
↵¹ The abbreviations used are:

IL-6

interleukin 6

sIL-6R

soluble IL-6 receptor

APRF

acute phase response factor

STAT

signal transducer and activator of transcription

Jak

Janus kinase

Epo

erythropoietin

EpoR

erythropoietin receptor

IFNγ

interferon-γ

IFNγR

interferon-γ receptor

DMEM

Dulbecco's modified Eagle's medium

EMSA

electrophoretic mobility shift assay

SIE

sis-inducible element.
↵²Hemmann, U., Gerhartz, C., Heesel, B., Sasse, J., Kurapkat, G., Grötzinger, J., Wollmer, A., Zhong, Z., Darnell, J. E., Jr., Graeve, L., Heinrich, P. C., and Horn, F. (1996) J. Biol. Chem. 271, 12999-13007.
- Received October 25, 1995.
- Revision received February 20, 1996.