Macrophage inhibitory cytokine-1 (MIC-1) has been reported to be elevated in various human cancers including melanoma; however, the function of MIC-1 in cancer remains unclear. In this study, we attempt to clarify the role of MIC-1 in tumor pathogenesis by employing the orthotopic B16F1 melanoma mouse model in which seru m MIC-1 levels are positively correlated with tumor size. By stably transfecting a MIC-1 expression construct into B16F1 melanoma cells, we increased the expression and secretion levels of MIC-1. This increase in MIC-1 expression significantly enhanced the growth of tumors derived from B16F1 cells in vivo, despite not affecting in vitro cell growth. The elevated MIC-1 expression in B16F1 cells also resulted in lymph node metastasis in B16F1 tumor-bearing mice, significantly increasing mortality. Interestingly, among small melanoma tumors of similar size, tumors derived from the MIC-1-transfected B16F1 cells exhibited enhanced blood vessel formation compared with those of mock transfectant cells. Also, more MIC-1 was found in well-vascularized tumor regions than in poorly vascularized tumor regions. Moreover, conditioned medium (CM) of the MIC-1-transfected melanoma cells enhanced the angiogenic properties of endothelial cells more than CM of mock transfectant cells. Notably, hypoxic culture conditions forced parental B16F1 cells to secrete more endothelial cell-stimulating factors, among which the function of MIC-1 was confirmed by blocking the effects with an anti-MIC-1 antibody. Taken together, these results suggest that the MIC-1 produced by melanoma cells in response to oxygen deprivation promotes tumor vascularization during melanoma development in vivo, leading to enhanced tumor growth and metastasis. * Jaeseob Lee and Young-June Jin contributed equally to the writing of this article. Received 29 March 2021 Accepted 22 September 2021 Correspondence to Hansoo Lee, PhD, Department of Biological Sciences, College of Natural Sciences, Kangwon National University, Chuncheon 24341, Republic of Korea, Tel: +82 33 250 8530; e-mail: hslee@kangwon.ac.kr Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.
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