title: Diminishment of alpha-MSH anti-inflammatory activity in MC1r siRNA-transfected RAW264.7 macrophages.
abstract: The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is a powerful suppressor of inflammation mediated by macrophages, which express at least two receptors, melanocortin 1 and 3 receptors (MC1r and MC3r) that bind alpha-MSH. Albeit, the anti-inflammatory activity of alpha-MSH has been well documented in macrophages, the mechanisms of alpha-MSH activity in macrophages are not clearly understood. This study is to investigate which of the MCr expressed on macrophages is associated with the immunosuppressive activities of alpha-MSH on LPS-stimulated macrophages. To address this question, we transfected RAW264.7 macrophage cells with MC1r small interfering (si)RNA, which specifically targets mouse MC1r mRNA. The diminution of MC1r mRNA expression was 82% at 24 h and 67% at 48 h after transfection. There was a significant loss in alpha-MSH suppression of NO generation and TNF-alpha production by MC1r siRNA-transfected macrophages stimulated with LPS. There was an equally diminished alpha-MSH suppression of LPS-stimulated intracellular activation of NF-kappaB and p38 phosphorylation. In addition, the diminishment of MC1r expression by siRNA transfection had no influence on MC3r expression and function in the macrophages. These findings demonstrate that alpha-MSH suppression of LPS-induced inflammatory activity in macrophages requires expression of MC1r. The results imply that although all of the MCr are G-coupled proteins, they may not necessarily function through the same intracellular pathways in macrophages.
authors.affiliation: Schepens Eye Research Institute, 20 Staniford Street, Boston, MA 02114, USA.
authors.forename: Dayu
authors.initials: D
authors.lastname: Li
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Taylor
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D002460:Cell Line; D020868:Gene Silencing / Q000187:drug effects; D007249:Inflammation; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism*; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism*; D044102:Receptor, Melanocortin, Type 1 / Q000235:genetics / Q000378:metabolism*; D044104:Receptor, Melanocortin, Type 3 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D000521:alpha-MSH / Q000494:pharmacology*
chemical_list: D000893:Anti-Inflammatory Agents; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D044102:Receptor, Melanocortin, Type 1; D044104:Receptor, Melanocortin, Type 3; D000521:alpha-MSH