SCRG1 suppresses LPS-induced CCL22 production through ERK1/2 activation in mouse macrophage Raw264.7 cells

Recently, we identified the scrapie responsive gene 1 (SCRG1) secreted from mesenchymal stem cells (MSCs) and its receptor bone marrow stromal cell antigen 1 (BST1) as positive regulators of stem cell qualities such as self-renewal, migration abilities, and osteogenic differentiation potential. Here, we examined the effect of the paracrine activity of SCRG1 in macrophages. The mouse macrophage-like cell line Raw264.7 expressed BST1/β1 or BST1/β2 integrin as possible SCRG1 receptors. Unexpectedly, recombinant SCRG1 did not enhance cell proliferation, migration, or adhesion in these macrophages. However, further examination of the effect of SCRG1 in Raw264.7 cells did reveal a potent anti-inflammatory effect whereby SCRG1 suppressed LPS-induced CCL22 production. SCRG1 also induced the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in these cells and, moreover, a mitogen-activated protein kinase (MAPK)/ERK kinase inhibitor U0126 significantly suppressed the effect of SCRG1 on LPS-induced chemokine CCL22 production. Taken together, these data indicate that SCRG1 signals through the MAPK pathway and suppresses the LPS signaling pathway. CCL22 is generally known to be chemotactic for monocytes, dendritic cells, natural killer cells and chronically activated T lymphocytes, suggesting that MSC-derived SCRG1 may block infiltration of these cells. A mechanism is proposed by which MSCs play their immunosuppressive role through suppressing chemokine expression in monocyte/macrophage lineage cells.