Resolution of inflammation is an active process which is important for maintaining or restoring homeostasis in response to inflammatory insult. Failure in resolution results in persistent and chronic inflammation which increases the risk of cancer development. Efferocytosis, an essential part of resolution of inflammation, is defined as phagocytic removal of apoptotic cells, especially neutrophils, at the inflamed site, thereby preventing exposure of tissue to toxic intracellular components. It is carried out by a distinct group of phagocytes including anti-inflammatory macrophages (M2 type). Therefore, M2 macrophages represent a key component of the cellular proresolving mechanism and a potential factor for prevention of inflammation-associated cancer. Dysregulation, often overexpression, of c-Myc drives dedifferentiation of cancer cells to acquire capacity for self-renewal and metastasis, which accounts for poor prognosis in cancer patients. A cytoplasmic N-terminal part of full length c-Myc, termed Myc-nick, has been reported to promote differentiation of myoblasts. In the present study, we investigated whether Myc-nick is involved in M2 macrophage polarization and promotion of efferocytosis. We found that ectopic expression of Myc-nick in mouse bone marrow derived macrophages (BMDM) promoted the M2 macrophage polarization through upregulation of interleukin 10 (IL-10) and peroxisome proliferator activated receptor gamma (PPARγ). Furthermore, overexpression of exogenous Myc-nick in BMDM increased capture of apoptotic cells by BMDM through upregulation of a class of phosphatidyl serine (PS) receptors including T-cell immunoglobulin and mucin domain containing 4 (Timd4). PS constitutes one of ‘eat-me’ signals carried by apoptotic cells. PS receptors present on the surface of macrophages are important to recognize, engulf and finally clear apoptotic cells via phagocytosis. In addition, Myc-nick-induced efferocytosis was found to be tightly associated with K (lysine) acetyltransferase 2A (Kat2a/Gcn5). This may lead to the acetylation of transcription factors that regulate expression of PS receptor proteins. In conclusion, activation of M2 macrophages by Myc-nick facilitates efferocytosis and hence resolution of inflammation, and this may suppress inflammation-associated cancer progression.
Citation Format: Xiancai Zhong, Ha-Na Lee, Young-Joon Surh. Myc-nick promotes efferocytosis through M2 macrophage polarization. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 825.