Tumor suppressor ARF regulates tissue microenvironment and tumor growth through modulation of macrophage polarization

// Lidia Jiménez-García 1 , Sandra Herranz 1 , María Angeles Higueras 1 , Alfonso Luque 1, * , Sonsoles Hortelano 1, * 1 Unidad de Terapias Farmacológicas. Instituto de Investigaciones de Enfermedades Raras (IIER), Instituto de Salud Carlos III, Madrid, Spain * These authors contributed equally to this work Correspondence to: Sonsoles Hortelano, email: shortelano@isciii.es Keywords: ARF, M2-polarization, tumor-microenvironment, angiogenesis, macrophage Received: March 15, 2016 Accepted: August 24, 2016 Published: August 27, 2016 ABSTRACT Tumor microenvironment has been described to play a key role in tumor growth, progression, and metastasis. Macrophages are a major cellular constituent of the tumor stroma, and particularly tumor associated macrophages (TAMs or M2-like macrophages) exert important immunosuppressive activity and a pro-tumoral role within the tumor microenvironment. Alternative-reading frame (ARF) gene is widely inactivated in human cancer. We have previously demonstrated that ARF deficiency severely impairs inflammatory response establishing a new role for ARF in the regulation of innate immunity. On the basis of these observations, we hypothesized that ARF may also regulates tumor growth through recruitment and modulation of the macrophage phenotype in the tumor microenvironment. Xenograft assays of B16F10 melanoma cells into ARF-deficient mice resulted in increased tumor growth compared to those implanted in WT control mice. Tumors from ARF-deficient mice exhibited significantly increased number of TAMs as well as microvascular density. Transwell assays showed crosstalk between tumor cells and macrophages. On the one hand, ARF-deficient macrophages modulate migratory ability of the tumor cells. And on the other, tumor cells promote the skewing of ARF–/– macrophages toward a M2-type polarization. In conclusion, these results demonstrate that ARF deficiency facilitates the infiltration of macrophages into the tumor mass and favors their polarization towards a M2 phenotype, thus promoting tumor angiogenesis and tumor growth. This work provides novel information about the critical role of ARF in the modulation of tumor microenvironment.