A novel miR-200b-3p/p38IP pair regulates monocyte/macrophage differentiation

Monocyte/macrophage differentiation represents a major branch of hematopoiesis and is a central event in the immune response, but the molecular mechanisms underlying are not fully delineated. Here we show that p38 mitogen-activated protein kinase (MAPK) interacting protein (p38IP) is downregulated during monocyte/macrophage differentiation in vitro. Overexpression of p38IP halted monocyte/macrophage differentiation, whereas forward knockdown of p38IP by RNA interference induced G1/S arrest and promoted monocyte differentiation into macrophages and the maturation of macrophages as well. Moreover, we found that miR-200b-3p was upregulated during monocyte/macrophage differentiation and mediated the downregulation of p38IP by binding to the 3' untranslated terminal region of p38IP mRNA. Overexpression of a miR-200b-3p mimic resembled the effect of p38IP knockdown, whereas a miR-200b-3p inhibitor blocked monocyte/macrophage differentiation by enhancing p38IP expression. Further western blotting analysis revealed that p38IP downregulation enhanced the activity of p38 MAPK and the subsequent accumulation of cyclin-dependent kinase inhibitor p21, thus promoting G1/S arrest and monocyte/macrophage differentiation. Moreover, the decline of GCN5 acetyltransferase caused by p38IP downregulation was required but was not sufficient for monocyte/macrophage differentiation. This study demonstrated a new role for p38IP and a novel miR-200b-3p/p38IP pair in the regulation of monocyte/macrophage differentiation.