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

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.

Promising landscape for regulating macrophage polarization: epigenetic viewpoint

“…Monocyte-macrophage lineage derives from myeloid precursors in bone marrow and subsequently develop as tissues-specific macrophages in response to local microenvironment signals [ 1 , 2 ]. Macrophages are heterogeneous and pleiotropic cells which can be generally polarized into M1-(classically activated) or M2-(alternatively activated) subtypes, which is a continuum of diverse functional states [ 3 , 4 ]. M1 phenotype could be triggered by lipopolysaccharide (LPS) and/or interferon (IFN)-γ andis believed to exert pro-inflammatory effects on tissue injury [ 5 , 6 ], which have the specific markers such as inducible NO synthesase (iNOS), interleukin(IL)-12 [ 7 , 8 ].…”

Tumor Suppressor p14ARF Enhances IFN-γ–Activated Immune Response by Inhibiting PIAS1 via SUMOylation

“…More recently, ARF was also shown to be transcriptionally induced in response to IFNs and viral stimulation (44,45). The significant p53-independent contribution of ARF to the innate immune response has since been highlighted by several studies (5,6,46,47). Proof of concept for ARF as a sensor and responder to viral stress was provided when García et al (5) demonstrated that ARF protects cells and mice from the infection of IFN-sensitive viruses.…”

“…Instead, they were polarized to produce the immunosuppressive and proangiogenic cytokines commonly associated with the maintenance of a protumor microenvironment. Arf-null tumors preferably recruited such macrophages to increase angiogenesis and promote their growth (46,47). Importantly, Arf-null mice were remarkably less able to recruit neutrophils and monocytes to the site of drug-induced peritonitis (6).…”

Melanoma from Molecular Pathways to Clinical Treatment: An Up to Date Review

“…P16 binds to cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) and inhibits phosphorylation of Rb, which remains associated with the transcription factor, E2F. Alternate reading frame protein (ARF) complexes with mouse double minute 2 homolog 2 (MDM2), an E3 ubiquitin ligase that regulates the stability of p53 and therefore suppressing tumor growth, it is also involved in the immune response, by modulating the tumor environment [46]. Therefore, mutation(s) in alternate reading frame protein dysregulate p53 function and play a role in tumor immune evasion.…”