Cold Shock Domain Proteins Repress Transcription from the GM-CSF Promoter

The human granulocyte-macrophage colony stimulating factor (GM-CSF) gene promoter binds a sequence-specific single-strand DNA binding protein termed NF-GMb. We previously demonstrated that the NF-GMb binding sites were required for repression of tumor necrosis factor-α (TNF-α) induction of the proximal GM-CSF promoter sequences in fibroblasts. We now describe the isolation of two different cDNA clones that encode cold shock domain (CSD) proteins with NF-GMb binding characteristics. One is identical to the previously reported CSD protein dbpB and the other is a previously unreported variant of the dbpA CSD factor. This is the first report of CSD factors binding to a cytokine gene. Nuclear NF-GMb and expressed CSD proteins have the same binding specificity for the GM-CSF promoter and other CSD binding sites. We present evidence that CSD factors are components of the nuclear NF-GMb complex. We also demonstrate that overexpression of the CSD proteins leads to complete repression of the proximal GM-CSF promoter containing the NF-GMb/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 two different mechanisms. We discuss the potential importance of CSD factors in maintaining strict regulation of the GM-CSF gene.