Actin cytoskeleton differentially modulates NF-κB-mediated IL-8 expression in myelomonocytic cells

Many physiopathological events such as phagocytosis, pathogen invasion, cellular adhesion and chemotaxis governed by actin-based cytoskeleton are often accompanied by nuclear factor κB (NF-κB) activation and expression of pro-inflammatory genes. In the present study, we demonstrated that reorganization of actin cytoskeleton induced by Cytochalasin D (CytD), an actin-polymerization inhibitor, enhanced il-8 gene expression induced by TNFα and LPS in HL-60 monocyte-like cells. Both transcriptional and post-transcriptional mechanisms were involved. CytD potentiated NF-κB-mediated transcription induced by both TNFα and LPS but via different mechanisms. In the case of LPS, the perturbation of actin dynamics increased the TLR4 levels at the cell membrane and consequently enhanced the IKK complex activation and NF-κB nuclear translocation. However, the canonical pathway involving the IKK complex and leading to the NF-κB translocation into the nucleus was not affected by actin remodelling in the case of TNFα. Interestingly, actin disruption primed p65 phosphorylation induced by TNFα and LPS, on Ser276 and Ser536, respectively, which suggested actin cytoskeleton could also modulate p65 transactivating activity.