THE REGULATORY MECHANISM OF HAEM OXYGENASE PROTECTION AGAINST PHOTOIMMUNOSUPPRESSION AND SKIN CANCER

目前的教条认为UVA辐射会增加皮肤中的UVB损伤。然而，我们已经确定了一个UVA剂量窗口，可以从白天的阳光照射中轻松获得，不会导致晒伤，也不会抑制免疫，但会显著减弱UVB的破坏作用。在小鼠中，该机制部分依赖于UVA上调的细胞因子干扰素-γ，强烈依赖于UVA诱导的抗氧化酶血红素加氧酶-1（HO-1）。该项目旨在确定HO-1基因是如何被UVA调节的。从培养的人类皮肤细胞的可用数据表明，HO-1是UVA诱导的成纤维细胞，但不是角质形成细胞，而我们发现这两种细胞类型的反应在小鼠皮肤，角质形成细胞最活跃。我们将确定是否物种差异，或培养细胞的异常，这些差异的基础。通过将人类皮肤移植到免疫缺陷的SCID小鼠上，我们将研究受损的免疫功能，这是癌症的重要先决条件，与体内小鼠皮肤进行比较。使用分子生物学技术与此模型，我们将监测的转录因子巴赫1，已知结合到HO-1启动子区的DNA抑制基因正常，但可逆的血红素结合，和相应的活性HO-1，在免疫保护（UVA暴露，血红素升高）条件。免疫保护作用可能是由于Bach 1与UVA从微粒体蛋白中释放的血红素结合，从DNA中释放，从而解除HO-1的抑制。我们将寻求证据的作用，皮肤细胞因子在修改巴赫1绑定，巴赫1和HO-1的行动在光致癌诱导与慢性紫外线照射。研究结果的意义在于理解UVA辐射诱导的自然改善途径如何用于皮肤癌易感人群的上级光保护策略。

Current dogma holds that UVA radiation adds to UVB damage in the skin. However we have identified a window of UVA doses, easily achievable from daytime sunlight exposure, that do not cause sunburn and are not immunosuppressive, but that significantly attenuate the damaging effects of UVB. In mice the mechanism partially depends on the UVA-upregulated cytokine interferon-gamma, and strongly on the UVA-inducible antioxidant enzyme haem oxygenase-1 (HO-1). This project aims to establish how the HO-1 gene is regulated by UVA. Available data from cultured human skin cells suggest that HO-1 is UVA-inducible in fibroblasts but not keratinocytes, whereas we found both cell types respond in mouse skin, keratinocytes most actively. We will ascertain whether a species difference, or an anomaly in cultured cells, underlies these discrepancies. With human skin grafted onto immunodeficient SCID mice, we will study impaired immune function, an important prerequisite for cancer, compared with mouse skin in vivo. Using molecular biology techniques with this model, we will monitor the activity of the transcription factor Bach 1, known to bind to the DNA of the HO-1 promoter region to repress the gene normally, but reversibly by haem-binding, and the corresponding activity of HO-1, during immunoprotective (UVA exposure, haem elevated) conditions. Immunoprotection may result from binding by Bach 1 of haem released from microsomal proteins by UVA, its release from DNA and thus derepression of HO-1. We will seek evidence of a role for skin cytokines in modifying Bach 1 binding, and for Bach 1 and HO-1 actions during photocarcinogenesis induction with chronic UV exposure. The significance of the outcome of the studies will be in understanding how a natural ameliorating pathway induced by UVA radiation could be utilised for superior photoprotection strategies for skin cancer susceptible humans.