ABSTRACT
IL-5, IL-3, and GM-CSF are hematopoietic cytokines that are key mediators of the allergic inflammatory response. The receptors for these three cytokines consist of a cytokine-specific alpha (Ralpha) chain and a shared common beta (betac) chain. Herein, we demonstrate that agonistic ligation of these receptor subunits rapidly induces proteasomal degradation of the betac, but not the Ralpha, cytoplasmic domain, resulting in termination of signal transduction and yielding a truncated betac isoform ligated to the Ralpha subunit. Proteasomal degradation of the betac cytoplasmic domain was also a prerequisite for endocytosis and lysosomal degradation of the ligated receptor subunits. Moreover, proteasome-dependent termination of signaling induced by one betac-engaging cytokine resulted in cellular desensitization to signal transduction by subsequent stimulation with another betac-engaging cytokine. These data provide the first evidence for ligand-dependent proteasomal degradation of the betac cytoplasmic domain, and they establish a novel mechanism for heterotypic desensitization of shared cytokine receptor signaling.
Subject(s)
Cysteine Endopeptidases/physiology , Milk Proteins , Multienzyme Complexes/physiology , Proto-Oncogene Proteins , Receptors, Cytokine/physiology , Signal Transduction , Alternative Splicing , DNA-Binding Proteins/physiology , Gene Expression Regulation , Granulocyte-Macrophage Colony-Stimulating Factor/pharmacology , Humans , Interleukin-3/pharmacology , Interleukin-5/pharmacology , Janus Kinase 2 , Proteasome Endopeptidase Complex , Protein-Tyrosine Kinases/physiology , RNA, Messenger/analysis , Receptors, Cytokine/analysis , Receptors, Interleukin/analysis , Receptors, Interleukin/genetics , Receptors, Interleukin-5 , STAT5 Transcription Factor , Trans-Activators/physiology , Tumor Cells, CulturedSubject(s)
Hypersensitivity/therapy , Inflammation/therapy , Interleukin-5/physiology , Animals , Asthma/etiology , Asthma/therapy , Eosinophils/immunology , Humans , Hypersensitivity/etiology , Inflammation/etiology , Interleukin-5/chemistry , Interleukin-5/genetics , Models, Molecular , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/physiology , Protein Structure, Tertiary , Receptors, Interleukin/chemistry , Receptors, Interleukin/genetics , Receptors, Interleukin/physiology , Receptors, Interleukin-5 , Signal TransductionABSTRACT
Cells express a variety of STAT (signal transducer and activator of transcription) transcription factors that are structurally homologous and yet function specifically in response to particular cytokines. The functions of the individual STATs are dependent on distinct protein-protein interactions. STAT1 and STAT2 are activated by tyrosine phosphorylation in response to type I interferons-alpha/beta (IFN-alpha/beta) and subsequently form a multimeric transcription factor designated the IFN-alpha-stimulated gene factor 3 (ISGF3). ISGF3 is a unique STAT complex because it also contains a non-STAT molecule, p48, which is a critical DNA-binding component. We provide evidence that STAT2 specifically interacts with p48 in vivo before and after IFN-alpha stimulation. The specificity of ISGF3 formation is therefore a result of the distinct nature of the STAT2 molecule. Coimmunoprecipitation assays demonstrate p48 association with STAT2 but not STAT1. Hybrid STAT2. STAT1 molecules were used to identify a region of STAT2 which specifically associates with p48. The region of STAT2 interaction spans an amino-terminal region of two predicted coiled coils. The studies demonstrate the in vivo existence of a STAT2.p48 complex and a distinct STAT2.STAT1 complex after IFN-alpha stimulation. Data suggest that distinct bipartite complexes STAT2.p48 and STAT2.STAT1 translocate to the nucleus and associate on the DNA target site as ISGF3.
Subject(s)
DNA-Binding Proteins/metabolism , Interferon-alpha/pharmacology , Trans-Activators/metabolism , Transcription Factors/metabolism , Animals , Binding Sites , HeLa Cells , Humans , Hybridomas/metabolism , Interferon-Stimulated Gene Factor 3 , Interferon-Stimulated Gene Factor 3, gamma Subunit , Mice , Protein Binding , Protein Conformation , STAT1 Transcription Factor , STAT2 Transcription Factor , Structure-Activity RelationshipABSTRACT
The activation of a latent DNA binding factor by interleukin-4 (IL-4), the IL-4 nuclear activated factor (IL-4 NAF), occurs within minutes of IL-4 binding to its receptor. Molecular characterization of IL-4NAF by ultraviolet light cross-linking experiments revealed a single protein of 120-130 kDa in contact with the DNA target site. Glycerol gradient sedimentation analysis indicated a molecular mass of IL-4 NAF consistent with a monomer that is capable of binding DNA. The IL-4 NAF target site is a palindromic sequence that is also recognized by the interferon-induced transcription factor, p91/STAT1 alpha. However, IL-4 NAF and p91/STAT1 alpha display distinguishable DNA binding specificities that may generate one level of specificity in the expression of target genes. Previous studies suggested the involvement of the insulin receptor substrate-1 (IRS-1) in the IL-4 signal transduction pathway. Although IRS-1 is involved in the stimulation of mitogenesis, our results demonstrate that activation of IL-4 NAF is independent of IRS-signaling proteins. The results of this study indicate that IL-4 stimulates bifurcating signal pathways that can direct mitogenesis via the IRS-signaling proteins and specific gene expression via the IL-4 NAF.
Subject(s)
DNA-Binding Proteins/metabolism , Interleukin-4/metabolism , Phosphoproteins/metabolism , Trans-Activators/metabolism , Transcription Factors/metabolism , Animals , Base Sequence , Cell Line , HeLa Cells , Humans , Insulin Receptor Substrate Proteins , Mice , Molecular Sequence Data , Oligodeoxyribonucleotides , Protein Binding , STAT1 Transcription Factor , Signal TransductionABSTRACT
A 59 year old man presented with symptoms of partial bowel obstruction. Small bowel x-ray studies did not allow to identify the nature of the intestinal process in the upper ileum. At laparotomy small bowel encapsulation with a whitish membrane was encountered. Despite partial removal of this membrane small bowel obstruction persisted and two weeks postoperatively the patient died of peritonitis and cardiac insufficiency. Autopsy findings revealed massive fibrous adhesions in the abdomen with granulomatous inflammation. The presence of foreign body giant cells and bifringent crystals were characteristic for talcum powder. The latter suggested a causal role of an appendectomy 45 years earlier. The diagnosis of sclerosing encapsulating peritonitis as established in our patient needs to be separated from peritoneal encapsulation, a congenital malformation, and abdominal cocoon, which contains histological elements of inflammation. This case report should draw attention to these entities in the differential diagnosis and surgical management of small bowel obstruction.
