LPS Does Not Directly Induce STAT Activity in Mouse Macrophages

Induction of gene expression in cytokine-treated cells involves the protein tyrosine kinase-dependent activation of members of the STAT family of transcription factors. To determine if lipopolysaccharide (LPS) might activate one or more STAT factors, nuclear extracts from LPS-treated RAW264.7 macrophages were assayed for STAT-like DNA binding activity using oligonucleotides recognized by different members of this protein family. Within 30 min a single LPS-inducible DNA–protein complex was detected using three separate oligonucleotides. This activity was not reactive with anti-STAT antibodies and was subsequently identified as composed of the NFκB components NFκB1 and Rel-A. Thus, LPS does not directly stimulate STAT factors with known sequence-specific DNA binding activity.