Radiotherapy is emerging as an important modality for the local control of pancreatic cancer, but pancreatic cancer cell radioresistance remains a serious concern. Peroxisome proliferator-activated receptor α (PPARα) is a member of the PPAR nuclear hormone receptor superfamily, which can be activated by fibrate ligands. The clinical relevance of PPARα and its biological function in pancreatic cancer radiosensitivity have not been previously described. In this study, we examined PPARα expression in tissue samples of pancreatic cancer patients. We found significantly higher expression of PPARα in pancreatic cancer tissues than in tumor-adjacent tissues and that the PPARα expression level is inversely associated with higher overall patient survival rate. We further observed that PPARα activation by its agonist clofibrate sensitizes pancreatic cancer cells to radiation by modulating cell cycle progression and apoptosis in several pancreatic cancer cell lines. Small interfering RNA-mediated PPARα silencing and PPARα blockade by the antagonist GW6471 abolish the effect of clofibrate on radiosensitization. An in vivo study showed that PANC1 xenografts treated with clofibrate are more sensitive to radiation than untreated xenografts. mRNA profiling by microarray analysis revealed that the expression of PTPRZ1 and Wnt8a, two core components of the β-catenin pathway, is downregulated by clofibrate. Chromatin immunoprecipitation analysis confirmed that clofibrate abrogates the binding of nuclear factor-κB to the PTPRZ1 and Wnt8a promoters, ultimately decreasing Wnt/β-catenin signaling activity, which is associated with radiosensitivity. Overall, we demonstrate that PPARα is overexpressed in pancreatic cancer tissues and clofibrate-mediated PPARα activation sensitizes pancreatic cancer cells to radiation through the Wnt/β-catenin pathway.
Models of human epidermis are widely employed for basic studies of skin biology and in the development of drugs and cosmetics, but epidermal equivalents prepared with passaged keratinocytes are typically only 10-20 mm thick, whereas full-thickness human epidermis can be up to 100 mm thick. Our established mathematical model of epidermal homeostasis predicted that the undulatory pattern of the papillary layer beneath the epidermis is a key determinant of epidermal thickness. Here, aiming to develop a more physiologically realistic epidermal model, we tested this prediction by seeding human keratinocytes on polyester textiles with various fiber-structural patterns in culture dishes exposed to air. Textile substrate with fiber thickness and inter-fiber distance similar to those of human papillary layer proved most effective, affording a three-dimensional epidermal-equivalent model with thick stratum corneum and intercellular lamellar lipid structure. Cells located around fibers of the textile were proliferating, as indicated by BrdU staining and expression of melanoma-associated chondroitin sulfate proteoglycan. Fillaggrin, loricrin, claudin 1 and ZO-1 were all appropriately expressed. Silencing of the transcriptional coactivator YAP (Yes-associated protein) with siRNA disturbed construction of the three-dimensional structure. This work provides simple methodology for production of high-quality, low-cost epidermal-equivalent models using passaged keratinocytes.
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