Background: Tumor-associated macrophages (TAMs) play key roles in the development of many malignant solid tumors including breast cancer. They are educated in the tumor microenvironment (TME) to promote tumor growth, metastasis, and therapy resistance. However, the phenotype of TAMs is elusive and how to regulate them for therapeutic purpose remains unclear; therefore, TAM-targeting therapies have not yet achieved clinical success. The purposes of this study were to examine the role of transcription factor EB (TFEB) in regulating TAM gene expression and function and to determine if TFEB activation can halt breast tumor development.
Methods: Microarrays were used to analyze the gene expression profile of macrophages (MΦs) in the context of breast cancer and to examine the impact of TFEB overexpression. Cell culture studies were performed to define the mechanisms by which TFEB affects MΦ gene expression and function. Mouse studies were carried out to investigate the impact of MΦ TFEB deficiency or activation on breast tumor growth. Human cancer genome data were analyzed to reveal the prognostic value of TFEB and its regulated genes.
Results: TAM-mimic MΦs display a unique gene expression profile, including significant reduction in TFEB expression. TFEB overexpression favorably modulates TAM gene expression through multiple signaling pathways. Specifically, TFEB upregulates suppressor of cytokine signaling 3 (SOCS3) and peroxisome proliferator-activated receptor γ (PPARγ) expression and autophagy/lysosome activities, inhibits NLRP3 (NLR Family Pyrin Domain Containing 3) inflammasome and hypoxia-inducible factor (HIF)-1α mediated hypoxia response, and thereby suppresses an array of effector molecules in TAMs including arginase 1, interleukin (IL)-10, IL-1β, IL-6 and prostaglandin E2. MΦ-specific TFEB deficiency promotes, while activation of TFEB using the natural disaccharide trehalose halts, breast tumor development by modulating TAMs. Analysis of human patient genome database reveals that expression levels of TFEB, SOCS3 and PPARγ are positive prognostic markers, while HIF-1α is a negative prognostic marker of breast cancer.
Conclusions: Our study identifies TFEB as a master regulator of TAMs in breast cancer. TFEB controls TAM gene expression and function through multiple autophagy/lysosome-dependent and independent pathways. Therefore, pharmacological activation of TFEB would be a promising therapeutic approach to improve the efficacy of existing treatment including immune therapies for breast cancer by favorably modulating TAM function and the TME.
Keywords: breast neoplasms; immunity; immunomodulation; innate; macrophages; tumor microenvironment.
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