RNA interference of interferon regulatory factor-1 gene expression in THP-1 cell line leads to Toll-like receptor-4 overexpression/activation as well as up-modulation of annexin-II.

Interferon regulatory factor-1 (IRF-1) is a candidate transcription factor for the regulation of the Toll-like receptor-4 (TLR-4) gene. Using a small interfering RNA-based (siRNA) process to silence IRF-1 gene expression in the leukemic monocytic cell line THP-1, we investigated whether such a modulation would alter TLR-4 expression and activation status in these cells. The siIRF-1 cells expressed elevated levels of TLR-4 mRNA and protein compared to controls by 90% and 77%, respectively. ICAM.1 protein expression and apoptosis levels were increased by 8.35- and 4.25-fold, respectively. The siIRF-1 cells overexpressed Bax mRNA compared to controls. Proteomic analysis revealed upmodulation of the Annexin-II protein in siIRF-1 THP-1 cells. Myelodysplastic syndrome (MDS) patients with an absence of full-length IRF-1 mRNA also overexpressed Annexin-II. It is plausible that this overexpression may lead to the activation of TLR-4 contributing to the increased apoptosis characterizing MDS.