Distinct domains of the human granulocyte-macrophage colony-stimulating factor receptor alpha subunit mediate activation of Jak/Stat signaling and differentiation.
The alpha subunit of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor has several isoforms that result from alternative splicing events. Two forms, alpha-1 and alpha-2, have intracytoplasmic sequences that are identical within a membrane-proximal domain but differ completely distally. Variant and mutated GM-CSF receptor alpha subunits, along with the beta subunit (beta(c) protein) were expressed in M1 murine leukemia cells. and the ability of the receptors to signal for differentiation events and to activate Jak/Stat signaling pathways was examined. All cell lines expressing both alpha and beta(c) proteins exhibited high-affinity binding of radiolabeled human GM-CSF. Receptor alpha subunits with intact membrane-proximal intracellular domains could induce expression of the macrophage antigen F4/80 and down-regulate the expression of CD11b. Addition of recombinant human GM-CSF to cells expressing alpha-1 subunits induced the expression of CD86 and tyrosine phosphorylation of Jak-2 and its putative substrates SHPTP-2, Stat-5, and the GM-CSF receptor beta(c) subunit. Cells containing alpha subunits that lacked a distal domain (term-3) or had the alternatively spliced alpha-2 distal domain showed markedly decreased ability to support tyrosine phosphorylation of Jak-2 and its substrates or to up-regulate CD86. Ligand binding induced stable association of the alpha-1 subunit and beta(c) protein. In contrast, the alpha-2 subunit did not stably associate with the beta(c) subunit. These data identify potential molecular mechanisms for differential signaling of the alpha-1 and alpha-2 proteins. The association of unique signaling events with the 2 active GM-CSF alpha subunit isoforms offers a model for variable response phenotypes to the same ligand.
Department of Medicine and the Center for Molecular Biology and Gene Therapy, Loma Linda University, Loma Linda, CA 92354, USA. mlilly@som.llu.edu
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D000818:Animals; D015703:Antigens, CD / Q000187:drug effects / Q000378:metabolism; D000943:Antigens, Differentiation / Q000187:drug effects* / Q000378:metabolism; D051940:B7-2 Antigen; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D053614:Janus Kinase 2; D016177:Macrophage-1 Antigen / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008894:Milk Proteins; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011505:Protein-Tyrosine Kinases / Q000378:metabolism* / Q000502:physiology; D011518:Proto-Oncogene Proteins; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000378:metabolism* / Q000502:physiology; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured
D015703:Antigens, CD; D000943:Antigens, Differentiation; D051940:B7-2 Antigen; C497964:CD86 protein, human; C497965:Cd86 protein, mouse; D004268:DNA-Binding Proteins; D016177:Macrophage-1 Antigen; D008562:Membrane Glycoproteins; D008894:Milk Proteins; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; C036763:monocyte-macrophage differentiation antigen; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2