Mechanisms of SOCS3 phosphorylation upon interleukin-6 stimulation. Contributions of Src- and receptor-tyrosine kinases.
The suppressors of cytokine signaling (SOCS) are negative feedback inhibitors of cytokine signal transduction. SOCS3 is a key negative regulator of interleuking-6 (IL-6) signal transduction. Furthermore, SOCS3 was shown to be phosphorylated upon treatment of cells with IL-2, and this has been reported to regulate its function and half-life. We set out to investigate whether SOCS3 phosphorylation may play a role in IL-6 signaling. Tyrosine-phosphorylated SOCS3 was detected upon treatment of mouse embryonic fibroblasts with IL-6. Interestingly, the observed SOCS3 phosphorylation does not require SOCS3 recruitment to phosphotyrosine (Tyr(P)) 759 of gp130, and the kinetics of SOCS3 phosphorylation do not match the activation kinetics of the Janus kinases. This suggests that other kinases may be involved in SOCS3 phosphorylation. Using Src and Janus kinase inhibitors as well as Src kinase-deficient mouse embryonic fibroblasts, we provide evidence that Src kinases, which we found to be constitutively active in these cells, are involved in the phosphorylation of IL-6-induced SOCS3. In addition, we found that receptor-tyrosine kinases such as platelet-derived growth factor receptor or epidermal growth factor receptor can very potently phosphorylate IL-6-induced SOCS3. Taken together, these results suggest that SOCS3 phosphorylation is not a JAK-mediated phenomenon but is dependent on the activity of other kinases such as Src kinases or receptor-tyrosine kinases, which can either be constitutively active or activated by an additional stimulus.
Institut für Biochemie, Rheinisch-Westfälische Technische Hochschule Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany.
Ulrike
U
Sommer
Christine
C
Schmid
Radoslaw M
RM
Sobota
Ute
U
Lehmann
Nigel J
NJ
Stevenson
James A
JA
Johnston
Fred
F
Schaper
Peter C
PC
Heinrich
Serge
S
Haan
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D050822:Cytokine Receptor gp130; D004815:Epidermal Growth Factor / Q000502:physiology; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D053616:Janus Kinase 3; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D053683:Oncostatin M; D010455:Peptides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors / Q000378:metabolism*; D018909:src Homology Domains / Q000502:physiology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*
C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D015703:Antigens, CD; D000970:Antineoplastic Agents; C494199:IL6ST protein, human; C494200:Il6st protein, mouse; D015850:Interleukin-6; D008562:Membrane Glycoproteins; C508351:OSM protein, human; C508352:Osm protein, mouse; D010455:Peptides; D010982:Platelet-Derived Growth Factor; D011720:Pyrazoles; D011743:Pyrimidines; D012097:Repressor Proteins; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors; D053683:Oncostatin M; D050822:Cytokine Receptor gp130; D004815:Epidermal Growth Factor; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; C507933:JAK3 protein, human; C507935:Jak3 protein, mouse; D053616:Janus Kinase 3; D019061:src-Family Kinases