Formation of GW/P bodies as marker for microRNA-mediated regulation of innate immune signaling in THP-1 cells

GW bodies (GWB, or P bodies) are cytoplasmic foci thought to result from microRNA (miRNA) regulation of mRNA targets and subsequent mRNA degradation. The purpose of this study is to examine the effects of lipopolysaccharide (LPS) stimulation of human monocytes on GW body formation, miRNA induction, miRNA target regulation, and downstream cytokine and chemokine expression. In response to LPS stimulation, the number of GWB consistently increased by 2 fold at 8 hours after stimulation and this increase was abolished when the miRNA-effector proteins Rck/p54 or argonaute 2 (Ago2) were depleted. Since the level of miR-146a increased from 19 fold up to 100 fold during LPS stimulation, the transfection of a miR-146a-mimic into THP-1 cells was examined to determine whether miR-146a alone can induce similar changes in GWB. The results showed transfected miR-146a could produce a comparable increase in the number of GWB and this was accompanied by a reduction in major cytokines/chemokines induced by LPS. These data show that the increase in size and number of GWB may serve as a biomarker for miRNA mediated gene regulation, and miR-146a plays a significant role in the regulation of LPS-induced cytokine production in THP-1 cells.