Down-regulation of Stathmin Is Required for the Phenotypic Changes and Classical Activation of Macrophages

• Published in: The Journal of biological chemistry Vol. 290; no. 31; pp. 19245 - 19260
• Main Authors: Xu, Kewei, Harrison, Rene E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 31.07.2015; American Society for Biochemistry and Molecular Biology
• Subjects: activation; Animals; CDC2 Protein Kinase - metabolism; Cell Biology; Cell Line; Cell Shape - immunology; Down-Regulation; innate immunity; Interferon-gamma - physiology; Lipopolysaccharides - pharmacology; macrophage; Macrophage Activation; Macrophages - immunology; Macrophages - metabolism; Mice; microtubule; microtubule-associated protein; Microtubules - metabolism; Phagocytosis; Phenotype; Proteasome Endopeptidase Complex; Protein Stability; Receptors, Complement - metabolism; Sheep, Domestic; stathmin; Stathmin - genetics; Stathmin - metabolism; Toll-Like Receptor 4 - metabolism; microtubule; phagocytosis; innate immunity; macrophage; microtubule-associated protein; activation; stathmin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.639625

Macrophages are important cells of innate immunity with specialized capacity for recognition and elimination of pathogens and presentation of antigens to lymphocytes for adaptive immunity. Macrophages become activated upon exposure to pro-inflammatory cytokines and pathogenic stimuli. Classical activation of macrophages with interferon-γ (IFNγ) and lipopolysaccharide (LPS) triggers a wide range of signaling events and morphological changes to induce the immune response. Our previous microtubule (MT) proteomic work revealed that the stathmin association with MTs is considerably reduced in activated macrophages, which contain significantly more stabilized MTs. Here, we show that there is a global decrease in stathmin levels, an MT catastrophe protein, in activated macrophages using both immunoblotting and immunofluorescent microscopy. This is an LPS-specific response that induces proteasome-mediated degradation of stathmin. We explored the functions of stathmin down-regulation in activated macrophages by generating a stable cell line overexpressing stathmin-GFP. We show that stathmin-GFP overexpression impacts MT stability, impairs cell spreading, and reduces activation-associated phenotypes. Furthermore, overexpressing stathmin reduces complement receptor 3-mediated phagocytosis and cellular activation, implicating a pivotal inhibitory role for stathmin in classically activated macrophages. Macrophage activation involves pronounced microtubule (MT) stabilization. Stathmin is degraded to enhance MT stabilization and allow robust activation in IFNγ-LPS-stimulated macrophages. MT stabilization by reduced stathmin levels is required for enhanced phagocytosis, signal transduction, and activation of macrophages. Understanding the nature and mechanisms of MT stabilization in activated macrophages is important for both immunology and cell biology fields.