The Role Of TGFβ Signaling In Ultraviolet Radiation (UVB)-Induced Cutaneous Inflammation And Carcinogenesis
Open Access
- Author:
- Ravindran, Anand
- Graduate Program:
- Pathobiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 10, 2013
- Committee Members:
- Adam Bleier Glick, Dissertation Advisor/Co-Advisor
Adam Bleier Glick, Committee Chair/Co-Chair
Gary H Perdew, Committee Member
Pamela Hankey Giblin, Committee Member
Sagarika Kanjilal, Committee Member
Zhi Chun Lai, Special Member - Keywords:
- Skin Cancer
Ultraviolet Radiation
Transforming Growth Factor-Beta
Inflammation
Dendritic cell
T lymphocyte Activation - Abstract:
- Inflammation is an integral component of carcinogenesis and chronic dysregulated inflammation is recognized as an important tumor promoter increasing cancer risk. Cytokines, chemokines and growth factors in the tissue microenvironment, play a critical role in regulating the immune response to foreign antigen or altered self-antigen. Ensuing tissue damage and tissue repair from inflammation contribute to tumor promotion in part by subversion of the protective immune response generated against the neoplastic antigens into a predominantly protumorigenic response. Environmental exposure to ultraviolet radiation (UVB) is the major cause of skin cancer and exposure at high doses can potently activate the immune system. UVB can act as a complete carcinogen in the skin by inducing mutations in the DNA and establishing a proinflammatory microenvironment. Transforming growth factor-β1 (TGFβ1) is a potent negative regulator of epithelial cell proliferation and a key immunoregulatory cytokine in the skin with a pivotal function in maintaining steady-state peripheral tolerance. Previous studies using the 2-stage skin carcinogenesis model with mice that have alterations in the TGFβ1 pathway showed that TGFβ1 can function as a tumor promoter as well as a tumor suppressor but its role in UVB-induced skin carcinogenesis is not known. To study the role of TGFβ signaling in UVB-induced cutaneous inflammation and carcinogenesis, we used a pharmacological inhibition model with SB431542 (SB), a small molecule inhibitor of TGFβ type I receptor kinase and a genetic abrogation model, CD11c-dnTGFβRII in which mice express a dominant negative human transforming growth factor beta receptor II gene under the control of a CD11c promoter (CD11c-DNR), specific for dendritic cells. UVB-induced skin tumor formation in Skin Hairless-1 mice (SKH1) was suppressed by topical treatment with SB, as were CD4 and CD8 Tumor infiltrating lymphocytes (TIL), and IFNγ+ TIL. However, there was no difference in the tumor size or tumor cell proliferation. To understand the mechanism of TGFβ modulation of tumoral immune response, we used acute and chronic models of UVB induced inflammation with SB. SB blocked acute and chronic UVB-induced skin inflammation, linked to reduced T cell activation and IFNγ secretion in the skin and skin draining lymph nodes suggesting that the difference in tumor inflammation could be critical to reduced tumor outgrowth when TGFβ1 signaling was blocked. Dendritic cells are professional antigen presenting cells forming the bridge between the innate and the adaptive immune system and are key mediators of cutaneous inflammation. TGFβ signaling is important for the development of Langerhans cells (LCs), the epidermal DC subset in the skin. It is also implicated in the steady state epidermal maintenance of LCs. However, the role of TGFβ signaling for immunostimulatory function of LCs or other dermal DC subsets in response to an inflammatory stimulus such as UV irradiation is not clear. When we studied the effect of SB on DCs in an acute UVB model, we found that SB blocked p-Smad2 induction in dermal DCs, the migration of CD103+ CD207+ and CD207- dermal DC subsets to the skin draining lymph nodes (SDLNs) and in an ex vivo ear explant assay. However, SB did not alter the p-Smad2+ percentage or the basal or UVB-induced migration of LCs implicating CD103+ CD207+ and CD207- dermal DC subsets as key DC populations for UVB-induced skin inflammation. To further determine the requirement of TGFβ signaling specifically in DCs, we used CD11c-DNR mice to study UVB-induced inflammation. Defective TGFβ signaling in DCs reduced the steady-state migration of all three DC subsets: LCs, CD103+ CD207+ and CD207- dermal DC subsets. Acute UVB irradiation, however, reduced the migration of only CD103+ CD207+ and CD207- dermal DC subsets to the SDLNs and CD207- subset in a similar ear explant assay in DNR mice compared to WT. This correlated with a reduction in p-Smad2+ and CD86high subset of dermal DCs. There was no difference in UVB-induced migration of LCs between WT and DNR mice. Finally, to test the physiological relevance of the UVB-induced migration of dermal DC subsets, we used a T cell driven pathological model of Contact Hypersensitivity. Defective TGFβ signaling in DCs in DNR mice led to an attenuated ear thickness response in CHS compared to WT. In addition, the synergistic increase in ear thickness, CD4, CD8 T cell activation and cytokine profile in the SDLNs in WTs with UVB plus CHS was significantly suppressed in DNR mice. Together, these results highlight the critical requirement of TGFβ signaling in DCs for an optimal cutaneous immune response to UV irradiation. In contrast to the well documented immunoinhibitory properties of TGFβ, these results suggest a model in which TGFβ signaling in DCs is important for UVB induced cutaneous inflammation as well as other cutaneous inflammatory responses mediated by dermal dendritic cells. Together, these studies highlight a novel tumor-promoting mechanism for TGFβ in UVB skin carcinogenesis.