Melanoma-specific bcl-2 promotes a protumoral M2-like phenotype by tumor-associated macrophages

Abstract

BackgroundA bidirectional crosstalk between tumor cells and the surrounding microenvironment contributes to tumor progression and response to therapy. Our previous studies have demonstrated that bcl-2 affects melanoma progression and regulates the tumor microenvironment. The aim of this study was to evaluate whether bcl-2 expression in melanoma cells could influence tumor-promoting functions of tumor-associated macrophages, a major constituent of the tumor microenvironment that affects anticancer immunity favoring tumor progression.MethodsTHP-1 monocytic cells, monocyte-derived macrophages and melanoma cells expressing different levels of bcl-2 protein were used. ELISA, qRT-PCR and Western blot analyses were used to evaluate macrophage polarization markers and protein expression levels. Chromatin immunoprecipitation assay was performed to evaluate transcription factor recruitment at specific promoters. Boyden chamber was used for migration experiments. Cytofluorimetric and immunohistochemical analyses were carried out to evaluate infiltrating macrophages and T cells in melanoma specimens from patients or mice.ResultsHigher production of tumor-promoting and chemotactic factors, and M2-polarized activation was observed when macrophages were exposed to culture media from melanoma cells overexpressing bcl-2, while bcl-2 silencing in melanoma cells inhibited the M2 macrophage polarization. In agreement, the number of melanoma-infiltrating macrophages in vivo was increased, in parallel with a greater expression of bcl-2 in tumor cells. Tumor-derived interleukin-1β has been identified as the effector cytokine of bcl-2-dependent macrophage reprogramming, according to reduced tumor growth, decreased number of M2-polarized tumor-associated macrophages and increased number of infiltrating CD4+IFNγ+and CD8+IFNγ+effector T lymphocytes, which we observed in response to in vivo treatment with the IL-1 receptor antagonist kineret. Finally, in tumor specimens from patients with melanoma, high bcl-2 expression correlated with increased infiltration of M2-polarized CD163+macrophages, hence supporting the clinical relevance of the crosstalk between tumor cells and microenvironment.ConclusionsTaken together, our results show that melanoma-specific bcl-2 controls an IL-1β-driven axis of macrophage diversion that establishes tumor microenvironmental conditions favoring melanoma development. Interfering with this pathway might provide novel therapeutic strategies.

Inhibition of Anti-Apoptotic Bcl-2 Proteins in Preclinical and Clinical Studies: Current Overview in Cancer

“…Increased levels of Bcl-2 expression have been also associated with resistance to different drugs including 5-fluorouracil in gastric cancer [23] cisplatin in ovarian cancer [24] and doxorubicin in osteosarcoma and chondrosarcoma [25,26]. In the last years, our group demonstrated that, in addition to its important role in the regulation of apoptosis and chemoresistance [27], Bcl-2 modulates in vitro and in vivo tumor migration, invasion, autophagy and angiogenesis [28][29][30][31][32][33], promotes a cancer stem-like cell phenotype [34], regulates the expression of microRNA and the activity of several transcription factors and their specific target genes [35][36][37], controls an interleukin-1β-driven axis of macrophage diversion that establishes tumor microenvironmental conditions favoring melanoma development [38] and is involved in mitochondrial mRNA homeostasis [39]. We and other authors demonstrated several non-canonical functions of Bcl-2, as well as other anti-apoptotic proteins, in an apoptosis-independent manner [40].…”

The Promise of Liquid Biopsy to Predict Response to Immunotherapy in Metastatic Melanoma

“…After its initial suc9cess in the treatment of metastatic melanoma, the clinical application of checkpoint inhibitors has rapidly spread to the majority of cancer cases with varying degrees of success. Among several cancer types, melanoma remains one of the most positively impacted by the use of these molecules, most likely because of its high mutational rate as well as to the frequent generation of an inflammatory microenvironment which together help establish appropriate conditions for the immune-system to respond ( 90 , 91 ). In stage IV melanoma, five year overall survival rates obtained with the combination of ipilimumab and nivolumab are currently up to 52% ( 92 ).…”

Targeting Tumor-Associated Macrophages to Increase the Efficacy of Immune Checkpoint Inhibitors: A Glimpse into Novel Therapeutic Approaches for Metastatic Melanoma

“…In in vitro three-dimensional models, IL-10 has been shown to be released also by melanoma cells leading to the induction of an M2-like phenotype in myeloid cells [ 15 ]. Furthermore, in melanoma cells, overexpression of bcl-2 correlated with the tumor ability to reprogram macrophage polarization toward M2 through bcl-2-dependent IL-1β production [ 16 ]. Modifications of the TME further increase the heterogeneity of M2-TAMs; even in the same tumor model, different subtypes of M2-TAMs could be distributed in different regions, i.e., M2a-, M2b-, and M2c-TAMs.…”