title: Distinct activities of suppressor of cytokine signaling (SOCS) proteins and involvement of the SOCS box in controlling G-CSF signaling.
abstract: Granulocyte-colony stimulating factor (G-CSF) induces proliferation of myeloid progenitor cells and controls their differentiation into mature neutrophils. Signal transducer and activator of transcription (STAT) proteins STAT3 and STAT5 are activated by G-CSF and play distinct roles in neutrophil development. Suppressor of cytokine signaling (SOCS) proteins are induced by STATs and inhibit signaling through various negative-feedback mechanisms. SOCS proteins can compete with docking of signaling substrates to receptors, interfere with Janus tyrosine kinase activity, and target proteins for proteasomal degradation. The latter process is mediated through the conserved C-terminal SOCS box. We determined the role of various SOCS proteins in controlling G-CSF responses and investigated the involvement of the SOCS box therein. We show that SOCS1 and SOCS3, but not CIS and SOCS2, inhibited G-CSF-induced STAT activation in human embryo kidney 293 cells. In myeloid 32D cells, SOCS1 and SOCS3 are induced by G-CSF. However, relative to interleukin-3-containing cultures, during G-CSF-induced neutrophilic differentiation, SOCS3 expression was further elevated, while SOCS1 levels remained constant. SOCS box deletion mutants of SOCS1 and SOCS3 were severely hampered in their abilities to inhibit STAT activation and to efficiently suppress colony formation by primary myeloid progenitors in response to G-CSF. These data demonstrate the importance of the SOCS box for the inhibitory effects of SOCS proteins on G-CSF signaling and show that among the different SOCS family members, SOCS3 is the major negative regulator of G-CSF responses during neutrophilic differentiation.
authors.affiliation: Institute of Hematology, Erasmus University Medical Center, Room Ee 1330c, Dr Molewaterplein 50, 3015 GE Rotterdam, The Netherlands.
authors.forename: Gert-Jan M
authors.initials: GJ
authors.lastname: van de Geijn
authors.forename: Judith
authors.initials: J
authors.lastname: Gits
authors.forename: Ivo P
authors.initials: IP
authors.lastname: Touw
mesh_terms: D015153:Blotting, Western; D001853:Bone Marrow / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D016179:Granulocyte Colony-Stimulating Factor / Q000378:metabolism* / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000166:cytology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008894:Milk Proteins; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008894:Milk Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; C106644:SOCS3 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D050799:STAT5 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D016179:Granulocyte Colony-Stimulating Factor