The Erk1/2-EGR1 signaling pathway is involved in lipopolysaccharide-induced transforming growth factor-beta 1 expression in mouse macrophages

Numerous studies have demonstrated that lipopolysaccharide (LPS) stimulates TGF-β1 expression. Although studies have implicated the NF-κB/METTL3/METTL14 transactivation/m6A-dependent and AMPK-dependent signaling pathways are engaged in this process in a variety of cell types, the underlying regulatory mechanism in murine macrophages is still not fully understood. To address this issue, in vitro studies were performed using the murine macrophage cell line, RAW264.7. The results showed that LPS challenge resulted in a significant increase in TGF-β1 expression at both mRNA and protein levels. Subsequent studies revealed that the MAPK (including p38, Erk1/2, and JNK) and NF-κB signaling pathways were activated in response to LPS stimulation, but only blocking the Erk1/2 singling pathway completely abolished LPS-induced TGF-β1 expression. Further studies revealed that the levels of a downstream regulator of the Erk1/2 pathway, EGR1, were significantly increased after LPS treatment, and its knockdown significantly reduced LPS-induced Tgf-β1 expression levels. Finally, dual luciferase reporter and ChIP-PCR assays confirmed that EGR1 is a key transcription factor in the regulation of Tgf-β1 expression by binding to its promoter region in response to LPS stimulation. In conclusion, we elucidated the molecular events by which LPS regulates TGF-β1 expression in murine macrophages through the Erk1/2-EGR1 signaling pathway. These findings provide a conceptually novel pathway for LPS-induced TGF-β1 expression beyond the known NF-κB/METTL3/METTL14 transactivation/m6A-dependent and AMPK-dependent signaling pathways.