Lack of RNase L attenuates macrophage functions

Macrophages are one of the major cell types in innate immunity against microbial infection. It is believed that the expression of proinflammatory genes such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and cyclooxygenase-2 (Cox-2) by macrophages is also crucial for activation of both innate and adaptive immunities. RNase L is an interferon (IFN) inducible enzyme which is highly expressed in macrophages. It has been demonstrated that RNase L regulates the expression of certain inflammatory genes. However, its role in macrophage function is largely unknown.

Bone marrow-derived macrophages (BMMs) were generated from RNase L(+/+)and (-/-) mice. The migration of BMMs was analyzed by using Transwell migration assays. Endocytosis and phagocytosis of macrophages were assessed by using fluorescein isothiocyanate (FITC)-Dextran 40,000 and FITC-E. coli bacteria, respectively. The expression of inflammatory genes was determined by Western Blot and ELISA. The promoter activity of Cox-2 was measured by luciferase reporter assays.

Lack of RNase L significantly decreased the migration of BMMs induced by M-CSF, but at a less extent by GM-CSF and chemokine C-C motif ligand-2 (CCL2). Interestingly, RNase L deficient BMMs showed a significant reduction of endocytic activity to FITC-Dextran 40,000, but no any obvious effect on their phagocytic activity to FITC-bacteria under the same condition. RNase L impacts the expression of certain genes related to cell migration and inflammation such as transforming growth factor (TGF)-β, IL-1β, IL-10, CCL2 and Cox-2. Furthermore, the functional analysis of the Cox-2 promoter revealed that RNase L regulated the expression of Cox-2 in macrophages at its transcriptional level. Taken together, our findings provide direct evidence showing that RNase L contributes to innate immunity through regulating macrophage functions.