Submitted December 11, 2002
Accepted February 19, 2003
GMCSF activates NF-
B via direct interaction of the GMCSF-receptor with IB kinase 
Karin Ebner, Alexander Bandion, Bernd R Binder, Rainer de Martin, and Johannes A Schmid*
Department of Vascular Biology and Thrombosis Research, University of Vienna, Vienna, Austria
Competence Center Bio-Molecular Therapeutics, Vienna, Austria
* Corresponding author; email: johannes.schmid{at}univie.ac.at.
GMCSF has a central role in proliferation and differentiation of hematopoetic cells. Furthermore, it influences the proliferation and migration of endothelial cells. GMCSF elicits these functions by activating a receptor consisting of a ligand-specific 
-chain and a 
-chain, which is common for GMCSF, IL-3 and IL-5. It is known that various signaling molecules such as Janus kinase 2 or transcription factors of the STAT family bind to the common -chain and initiate signaling cascades. However, -chain specific signal transduction adapters have to be postulated given that IL-3, IL-5 and GMCSF induce partly distinct biological responses. Using a yeast two-hybrid system, we identified the -chain of the GMCSF receptor as putative interaction partner of I
B kinase , one of the central signaling kinases activating the transcription factor NF-B. Using endogenous protein levels of endothelial cell extracts, we could verify the interaction by co-immunoprecipitation experiments. Fluorescence resonance energy transfer (FRET) microscopy confirmed the direct interaction of CFP-IKK and YFP-GMR in living cells. Functional studies demonstrated GMCSF-dependent activation of IB kinase activity in endothelial cells, degradation of IB and activation of NF-B. Further biological studies using GMCSF-dependent TF-1 cells indicated that GMCSF-triggered activation of NF-B is important for cell survival and proliferation.
