Abstract 4081: Stromal autophagy is required for the growth of cutaneous melanoma

Abstract

Abstract Through degrading bulk cytoplasmic materials into intermediate building blocks, autophagy refuels metabolism and maintains homeostasis under starvation and stress conditions. The context-dependent role of autophagy in cancer cells during tumorigenesis and tumor progression has been explored over the past decade; however, studies of autophagy in relation to the tumor microenvironment are still lacking. In this study, we investigated the role of autophagy in the cancer-associated fibroblasts (CAFs), a major component of the microenvironment that is important for the growth and development of cutaneous melanoma. Analysis of clinical biopsies revealed high levels of autophagy in fibroblasts that surrounded melanoma cells, but not in the non-tumor adjacent area. Fibroblasts co-cultured with any of multiple melanoma cell lines, but not melanocytes, also showed increased autophagic flux, which requires transforming growth factor beta (TGF-β) signaling. Knocking down autophagy-related (ATG) genes ATG5 or ATG7 in fibroblasts did not impair their proliferation in vitro, but inhibited the growth of co-engrafted melanoma cells in vivo. Further, by introducing intradermal melanoma allografts into mice that harbored fibroblast-specific Atg7 deletion, we observed remarkable tumor growth retardation. In order to mimic anti-autophagy therapy for patients, we generated mice that allowed conditional Atg7 depletion in their entire bodies, and found significant tumor growth suppression. Atg7 knockout mice contained elevated plasma levels of immune cell attractants, including CXCL9, CXCL10 and MCP-1. By inhibiting these cytokines/chemokines with atorvastatin, tumor growth in Atg7 knockout mice was completely rescued; while, there was no effect of atorvastatin on control mice. Taken together, our data show that through modulating the tumor microenvironment, stromal autophagy plays an important role during melanoma growth and development. Our findings indicate that stromal autophagy may represent a valuable therapeutic target that might induce less side effects and systemic toxicity. Citation Format: Ran Ellen Zhang, Natalie J. Guo, Nithya Krishnan, David Jelinek, Gizem Karsli Uzunbas, Xiaoqi Xie, Arek Gertych, Janice M. Mehnert, Beatrice Knudsen, Eileen White, Hilary A. Coller. Stromal autophagy is required for the growth of cutaneous melanoma. [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 4081.