COLD SHOCK DOMAIN PROTEINS REPRESS TRANSCRIPTION FROM THE GM-CSF PROMOTER

The human granulocyte-macrophage colony stimulating factor (GM-CSF) ge ne promoter binds a sequence-specific single-strand DNA binding protei n termed NF-GMb, We previously demonstrated that the NF-GMb binding si tes were required for repression of tumor necrosis factor-alpha (TNF-a lpha) induction of the proximal GM-CSF promoter sequences in fibroblas ts, We now describe the isolation of two different cDNA clones that en code cold shock domain (CSD) proteins with NF-GMb binding characterist ics. One is identical to the previously reported CSD protein dbpB and the other is a previously unreported variant of the dbpA CSD factor, T his is the first report of CSD factors binding to a cytokine gene, Nuc lear NF-GMb and expressed CSD proteins have the same binding specifici ty for the GM-CSF promoter and other CSD binding sites. We present evi dence that CSD factors are components of the nuclear NF-GMb complex, W e also demonstrate that overexpression of the CSD proteins leads to co mplete repression of the proximal GM-CSF promoter containing the NF-GM b/CSD binding sites. Surprisingly, we show that CSD overexpression can also directly repress a region of the promoter which apparently lacks NF-GMb/CSD binding sites, NF-GMb/CSD factors may hence be acting by t wo different mechanisms, We discuss the potential importance of CSD fa ctors in maintaining strict regulation of the GM-CSF gene.