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

目前的观点认为，UVA辐射会增加UVB对皮肤的伤害。然而，我们已经确定了一个UVA剂量窗口，很容易从白天的阳光照射中获得，不会引起晒伤，也不会抑制免疫，但可以显著减弱UVB的破坏性影响。在小鼠中，其机制部分依赖于uva上调的细胞因子干扰素- γ，并强烈依赖于uva诱导的抗氧化酶血红素加氧酶-1 （HO-1）。本项目旨在确定UVA如何调控HO-1基因。从培养的人皮肤细胞中获得的现有数据表明，HO-1在成纤维细胞中是uva诱导的，而在角质形成细胞中则不是，而我们发现这两种细胞类型在小鼠皮肤中都有反应，角质形成细胞最活跃。我们将确定是物种差异还是培养细胞的异常导致了这些差异。我们将人类皮肤移植到免疫缺陷的SCID小鼠身上，研究免疫功能受损，这是癌症发生的重要前提，并与小鼠皮肤在体内进行比较。利用分子生物学技术和该模型，我们将监测转录因子巴赫1的活性，已知巴赫1与HO-1启动子区域的DNA结合，正常地抑制基因，但通过血液结合可逆地抑制基因，以及在免疫保护（UVA暴露，血红素升高）条件下HO-1的相应活性。免疫保护可能是由于UVA将微粒体蛋白释放的血红素与Bach -1结合，将其从DNA中释放出来，从而降低HO-1的表达。我们将寻找皮肤细胞因子在调节Bach -1结合中的作用，以及在慢性紫外线照射诱导光致癌过程中Bach -1和HO-1的作用。这些研究结果的意义在于了解UVA辐射诱导的自然改善途径如何被用于皮肤癌易感人群的优越光防护策略。

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.