Type III TGF-β receptor downregulation generates an immunotolerant tumor microenvironment.
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Cancers subvert the host immune system to facilitate disease progression. These evolved immunosuppressive mechanisms are also implicated in circumventing immunotherapeutic strategies. Emerging data indicate that local tumor-associated DC populations exhibit tolerogenic features by promoting Treg development; however, the mechanisms by which tumors manipulate DC and Treg function in the tumor microenvironment remain unclear. Type III TGF-β receptor (TGFBR3) and its shed extracellular domain (sTGFBR3) regulate TGF-β signaling and maintain epithelial homeostasis, with loss of TGFBR3 expression promoting progression early in breast cancer development. Using murine models of breast cancer and melanoma, we elucidated a tumor immunoevasion mechanism whereby loss of tumor-expressed TGFBR3/sTGFBR3 enhanced TGF-β signaling within locoregional DC populations and upregulated both the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) in plasmacytoid DCs and the CCL22 chemokine in myeloid DCs. Alterations in these DC populations mediated Treg infiltration and the suppression of antitumor immunity. Our findings provide mechanistic support for using TGF-β inhibitors to enhance the efficacy of tumor immunotherapy, indicate that sTGFBR3 levels could serve as a predictive immunotherapy biomarker, and expand the mechanisms by which TGFBR3 suppresses cancer progression to include effects on the tumor immune microenvironment.
Published Version (Please cite this version)
Hanks, Brent A, Alisha Holtzhausen, Katherine S Evans, Rebekah Jamieson, Petra Gimpel, Olivia M Campbell, Melissa Hector-Greene, Lihong Sun, et al. (2013). Type III TGF-β receptor downregulation generates an immunotolerant tumor microenvironment. J Clin Invest, 123(9). pp. 3925–3940. 10.1172/JCI65745 Retrieved from https://hdl.handle.net/10161/13297.
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We are interested in understanding the mechanisms that cancers have evolved to suppress the generation of tumor antigen-specific immune responses and how this knowledge can be exploited for the development of novel and more effective cancer immunotherapy strategies. This work involves the utilization of both autochthonous transgenic tumor model systems as well as clinical specimens to develop novel strategies to enhance the efficacy of immunotherapies while also developing predictive biomarkers to better guide the management of cancer patients with these agents. We strive to translate our understanding of the fundamental biochemical and metabolic pathways within the tumor microenvironment that are critical for driving immune evasion and resistance into early phase clinical trial testing.
Our work utilizes a variety of techniques and methodologies that span the breadth of basic biological research. This work integrates studies based on both 1) transgenic mouse tumor models that are monitored using bioluminescence and micro-CT imaging and 2) a variety of clinical specimens.
Our current areas of focus include:
- Investigating mechanisms of adaptive or acquired immunotherapy resistance in cancer
- Studying the relationship between EMT pathways and immunotherapy resistance.
- Elucidating mechanisms of dendritic cell tolerization in the tumor microenvironment and how these processes may contribute to immunotherapy resistance
- Development of novel pharmacologic and genetic strategies to overcome immunotherapy resistance
- Investigating mechanisms contributing to select immunotherapy-associated toxicities
Our laboratory focuses on transforming growth factor-ß (TGF-ß) superfamily signal transduction pathways, and specifically, the role of these pathways in cancer biology. The TGF-ß superfamily is comprised of a number of polypeptide growth factors, including TGF-βs, bone morphogenetic proteins (BMPs) and activin) that regulate growth, differentiation and morphogenesis in a cell and context specific manner. TGF-ß and the TGF-ß signaling pathway have a dichotomous role in cancer biology, as both tumor-suppressor genes (presumably as regulators of cellular proliferation, differentiation and apoptosis) and as tumor promoters (presumably as regulators of cellular motility, adhesion, angiogenesis and the immune system). This dichotomy of TGF-ß function remains a fundamental problem in the field both in terms of understanding the mechanism of action of the TGF-ß pathway, and directly impacting our ability to target this pathway for the chemoprevention or treatment of human cancers. Resistance to the tumor suppressor effects of TGF-ß is also a common feature of epithelial-derived human cancers (breast, colon, lung, pancreatic, prostate), however, mechanisms for TGF-ß resistance remain undefined in the majority of cases. TGF-ß regulates cellular processes by binding to three high affinity cell surface receptors, the type I, type II, and type III receptors. Recent studies by our laboratory and others have established the type III TGF-ß receptor (TßRIII) as a critical mediator/regulator of TGF-ß signaling. Specifically we have demonstrated that regulating TßRIII expression levels is sufficient to regulate TGF-ß signaling, and that decreased TßRIII expression is a common phenomenon in human cancers, resulting in cancer progression. TßRIII is also shed from the surface to generate soluble TßRIII, which we have demonstrated has a role in creating an immunotolerant tumor microenvironment. The role of TßRIII and soluble TßRIII in the tumor immune microenvironment is currently being investigated using a multidisciplinary approach.
Activin receptor-like kinase 4 (ALK4) is a type I transforming growth factor-β (TGF-β) superfamily receptor that mediates signaling for several TGF-β superfamily ligands, including activin, Nodal and GDF5. We have demonstrated that mutation or copy number loss of ALK4 occurs in 35% of pancreatic cancer patients, with loss of ALK4 expression associated with a poorer prognosis. ALK4 has also been identified in an unbiased screen as a gene whose disruption enhances Ras mediated pancreatic tumorigenesis in vivo. We have demonstrated that loss of ALK4 expression increases canonical TGF-β signaling to increase cancer invasion and metastasis in vivo. We are currently investigating the mechanism by which loss of ALK4 regulates TGF-β signaling, how it may effect other signaling pathways, and how to use this knowledge to treat pancreatic cancer patients with loss of ALK4 function.
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