Modulation of the Interleukin-6 Receptor Subunit Glycoprotein 130 Complex and Its Signaling by LMO4 Interaction

• Published in: The Journal of biological chemistry Vol. 280; no. 13; pp. 12747 - 12757
• Main Authors: Novotny-Diermayr, Veronica, Lin, Baohong, Gu, Lei, Cao, Xinmin
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2005; American Society for Biochemistry and Molecular Biology
• Subjects: Adaptor Proteins, Signal Transducing; Animals; Antigens, CD - chemistry; Antigens, CD - physiology; Blotting, Northern; Cell Line; Cell Line, Tumor; Cell Nucleus - metabolism; COS Cells; Cytokine Receptor gp130; Cytokines - metabolism; Cytoplasm - metabolism; DNA-Binding Proteins - metabolism; Down-Regulation; Gene Silencing; Genes, Reporter; Glutathione Transferase - metabolism; Homeodomain Proteins - chemistry; Homeodomain Proteins - physiology; Humans; Immunoprecipitation; Intracellular Signaling Peptides and Proteins; LIM Domain Proteins; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - physiology; Microscopy, Fluorescence; Phosphorylation; Plasmids - metabolism; Protein Binding; Protein Phosphatase 2; Protein Structure, Tertiary; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatases - chemistry; RNA, Small Interfering - metabolism; Signal Transduction; STAT3 Transcription Factor; Trans-Activators - metabolism; Transcription Factors - chemistry; Transcription Factors - physiology; Transfection; Two-Hybrid System Techniques; Tyrosine - chemistry; Tyrosine - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M500175200

The interleukin (IL)-6-type cytokines play major roles in a variety of biological processes by signaling through a common receptor subunit, glycoprotein (gp) 130. We performed yeast two-hybrid screening to identify new binding partners of the activated gp130 and the associated Janus kinases. LMO4, a LIM domain-containing protein that belongs to a family of oncogenes, was identified in this assay. Further studies show that LMO4 associates with gp130 and Janus kinase1 in several mammalian cell types. It also interacts with protein-tyrosine phosphatase 2 (SHP2) and suppressor of cytokine signaling 3 (SOCS3). The binding domains involved in these interactions were mapped, and the interactions were shown to be in a direct manner by in vitro binding assays. It is likely that LMO4 exists in the gp130 complex. The cellular localization of LMO4 was detected primarily in the nucleus with a substantial amount also detected in the cytoplasm in several cell types. The effect of LMO4 in IL-6 signaling was subsequently examined. Overexpression of LMO4 enhanced the transcriptional activity and target gene expression of Stat 3 (signal transducers and activators of transcription 3). Consistent with this, silencing LMO4 expression in stable cell lines expressing the small interfering RNA of LMO4 decreased Stat3 activity. Furthermore, the half-life of gp130 was shortened, and the production of acute phase proteins induced by IL-6 was reduced. Together, our data reveal a positive regulatory role of LMO4 in IL-6 signaling, possibly by acting as a scaffold for stabilization of the gp130 complex. These studies may open up a link between the oncogenic effect of LMO proteins and their regulatory role in cytokine signaling in general.