17 - Frontiers in Molecular Mechanisms of Skin Photocarcinogenesis
Florida 2 08:00 - 10:00
|Chair(s): Yu-ying He|
08:00 Immune mechanisms of p53 mutant keratinocyte clonal expansion and cutaneous carcinogenesis J Lewis, Yale University
; J Turban, Yale University; M Girardi*, Yale University
Abstract: We have recently demonstrated that keratinocyte (KC)-derived malignancy induced by chronic UVB exposure is facilitated by Langerhans cells (LC), and that LC promotion of clonal expansion of p53-mutant KC is correlated to epidermal growth factor IL-22 expression, in a T-cell independent manner. Thus, to better understand the mechanisms of innate immunity in LC-facilitated UV-carcinogenesis, we characterized innate lymphoid cells (ILC) in the presence and absence of LC, before and after chronic UVB exposure. Flow cytometric analysis of ILC transcription factors and cytokine expression revealed that among skin-isolated ILC (CD45+ Thy1+ CD11b- CD11c- B220- Gr1- Fc-epsilon-R1- Ter119-) from untreated LC-intact mice, the predominant subsets identified were (T-bet+) ILC1 and (Gata-3+) ILC2, while (Eomes+) cNK and (Rorc+) ILC3 were relatively infrequent. However, this distribution was dramatically altered by chronic UVB exposure that resulted in reduced T-bet+, Eomes+ and Gata-3+ populations and a marked increase in Rorc+ ILC3. Examination of cytokine expression following chronic UVB exposure revealed markedly increased levels of IL-22+ ILC, the majority of which co-expressed IL-17A+, while levels of IFNγ+ and IL-13+ ILC remained relatively low. IFNgamma-producing cells were CD2+ CCR6- and primarily Sca1- whereas IL-13, IL-22 and IL-17A were produced by Sca1-bright CCR6-dim cells. The majority of IL-22+ and IL-17A+ cells also expressed CD2. Notably, LC-deficiency was associated with a marked reduction in the frequency of IL-13+ ILC2 and IL-22+ ILC3. These results help elucidate cutaneous ILC phenotypic populations under chronic UV exposure and under LC influences, and suggest that LC and IL-22-producing ILC3 cooperate to make fundamental contributions to skin cancer development by facilitating clonal expansion of p53-mutant keratinocytes.
08:20 Engineering Bioadhesive Biodegradable Nanoparticle Encapsulation of Organic Sunscreen Agents to Enhance Their Performance and Safety M Girardi*, Yale University
; Y Deng, Yale University; A Ediriwickrema, Yale University; J Lewis, Yale Unversity; HW Suh, Yale University; Linda Fong, Yale University; WM Saltzman, Yale University
Abstract: Skin cancer is the most common malignancy in the USA, and exposure to the sun's ultraviolet radiation (UVR) is the primary risk factor. Therefore, strategies designed to protect the skin from UVR exposure, including topically applied sunscreens, may markedly decreased the incidence of and costs associated with skin cancer. The ideal sunscreen formulation might be expected to provide all-day, broad UVA/UVB, waterproof/sweatproof protection from a single application, and as well appease any safety concerns by preventing penetration of the organic active ingredients into the skin cells and blood stream. Towards these goals, we have developed and are assessing the efficacy of encapsulation of organic sunscreen agents into biodegradable, bioadhesive nanoparticles (BNPs). BNPs were designed with a polylactic acid core linked to a hyperbranched polyglycerols corona that was terminated with aldehydes after exposure to sodium periodate. Upon application the skin, the BNPs form covalent bonding to the stratum corneum with uniform coverage. In pre-clinical testing, relative to commercially available sunscreen, BNP-encapsulated sunscreen showed superior substantivity, the capacity to prevent any detectable skin absorption of the active organic agent, and protection against UVR-induced cyclobutane pyrimidine dimer formation. Importantly, reactive oxygen species (ROS)-induced DNA damage following UVR exposure was clearly evident with commercial sunscreen, but owing to the prevention of penetration, absent with the BNP formulation. Thus, formulations utilizing BNP-encapsulation may enhance the performance and safety of the currently approved sunscreen agents.
08:40 Regulation of UVB-induced carcinogenesis by Apigenin and Thrombospondin-1 X Tong, Northwestern University University, Chicago, IL, USA
; S Mirzoeva, Northwestern University; B Bridgeman, Northwestern University; D Veliceasa, Stanley Manne Children's Research Institute; SE Crawford, North Shore University Research Institute; M Cornwell, North Shore University Research Institute; OV Volpert*, Northwestern University University, Chicago, IL, USA
Abstract: Ultraviolet B (UBV) radiation is the main cause of non-melanoma skin cancer, which is increasingly prevalent of late despite the use of sunblock. Thus new agents and mechanisms useful for prevention or treatment of UVB-induced cancer are highly important. Endogenous angiogenesis inhibitor thrombospondin-1 (TSP1) is expressed by the epidermal keratinocytes and its critical role in cutaneous angiostasis is well known. Importantly, TSP1 expression is potently inhibited by UVB. Plant-derived bioflavonoid apigenin is a nutraceutical chemopreventive agent with anti-proliferative and anti-angiogenic effects, which inhibits UVB-induced carcinogenesis in skin through multiple mechanisms. We discovered that apigenin restores TSP1 expression in UVB-irradiated keratinocytes and skin. Using TSP1-null hairless mice we have shown that endogenous TSP1 has protective role in UVB-induced carcinogenesis and is critical for chemopreventive effect of apigenin in skin. We showed dramatic increases in UVB-induced cutaneous angiogenesis and inflammation in the absence of TSP1. Moreover, restoring TSP1 activity in UVB-irradiated skin with bioactive peptide mimetic was sufficient to recapitulate wide variety of apigenin's effects in UVB-exposed skin including its anti-angiogenic, anti-inflammatory and anti-proliferative actions. Seeking mechanisms underlying TSP1 regulation by the UVB and apigenin, we identified miRNA-dependent downregulation of TSP1 mRNA. Apigenin restored TSP1 expression through increased cytoplasmic presence of the RNA-binding protein HuR, where it bound TSP1 mRNA and resulted de novo synthesis of TSP1 protein. Together, our data provide new mechanism by which apigenin restores cutaneous homeostasis and prevents UVB-induced carcinogenesis.
09:00 Lack Of Tumor Development In C/EBPβ Knockout Mice After UVB Exposure Involves Increased Apoptosis And Decreased EGFR And ERK1/2 Expression And Phosphorylation S Anand*, Cleveland Clinic
; EV Maytin, Cleveland Clinic
Abstract: The CCAAT/Enhancer Binding Proteins (C/EBPs) are a family of six (C/EBP α, β, γ, δ, ε, andζ) leucine zipper transcription factors that control normal functions such as regulation of cell cycle, metabolism and differentiation. Recently, the involvement of these factors in cancer, inflammation, apoptosis and ER stress has been established. In current study we investigated the role of C/EBPβ in carcinogenesis induced by sun exposure. Although, C/EBPβ has been involved in the regulation of skin development and differentiation, its role in skin carcinogenesis is not clear. To investigate the role of C/EBPβ in UVB-carcinogenesis, C/EBPβ knockout mice (C/EBPβ KO), along with their heterozygote (Het) and wild type (WT) littermates, were exposed to UVB (progressively increasing doses up to 175 mJ/cm2 UVB, 3 times a week) for 20 weeks. At week 25, each WT mice had developed many tumors, whereas C/EBPβ KO mice completely lacked tumor development. As anticipated, Het mice had an intermediate response. To characterize the short-term events following UVB exposure that would eventually contribute to the tumor phenotype, mice were exposed to UVB (100 mJ/cm2) and skin was harvested at different times for analyses by immunohistochemistry and western blot. An enhanced apoptosis response (TUNEL and Caspase-3 cleavage) and elevated expression levels of TNFα were observed in C/EBPβ KO epidermis. Additionally, the expression and phosphorylation of EGFR and ERK1/2 were down regulated in C/EBPβ KO epidermis, as compared with their WT littermates. The observation of enhanced apoptotic response via the extrinsic pathway involving TNFα upregulation and compromised EGFR and ERK1/2 signaling were postulated as the mechanism underlying the lack of tumor response in C/EBβ KO mice. Our results suggest that in addition to its well-established functions in skin physiology, C/EBPβ may also play an important role in skin carcinogenesis involving the regulation of apoptotic and survival pathways.
09:20 Autophagy regulates UV-induced DNA damage repair and controls photocarcinogenesis Yu-Ying He*
Abstract: Autophagy is a cellular catabolic process that is essential for maintaining tissue homeostasis and regulating various normal and pathologic processes in human diseases including cancer. One cancer-driving process is accumulation of genetic mutations due to impaired DNA damage repair, including nucleotide excision repair that removes DNA damage caused by UV radiation and other chemicals. Here we show that autophagy positively regulates nucleotide excision repair through enhancing DNA damage recognition by the DNA damage sensor proteins XPC and DDB2 via two pathways. First, autophagy deficiency down-regulates the transcription of XPC through TWIST1-dependent activation of the transcription repressor complex E2F4/RBL2. Second, autophagy deficiency impairs the recruitment of DDB2 to UV-induced DNA damage sites through TWIST1-mediated inhibition of EP300. In mice, the pharmacological autophagy inhibitor Spautin1 promotes UVB-induced tumorigenesis, whereas the autophagy inducer rapamycin reduces UVB-induced tumorigenesis. These findings demonstrate the crucial role of autophagy in maintaining proper nucleotide excision repair in mammalian cells and suggest a previously unrecognized tumor-suppressive mechanism of autophagy in cancer.