SYNERGISTIC CARCINOGENICTY OF UVA AND BENZO(A)PYRENE

阳光暴晒和多环芳烃(PAHs)与人类皮肤癌有关。据推测，过度暴露于长波紫外线A(UVA)和吸烟或环境污染产生的多环芳烃可能与皮肤癌的惊人增加有关。这一建议的中心假设是，广泛存在的环境污染物苯并(A)芘(BaP)作为光敏剂，在UVA辐射下产生活性氧(ROS)。BaP-UVA处理产生的ROS诱导DNA氧化损伤，增强BaP-DNA加合物的形成(遗传效应)，并激活信号转导级联(表观遗传效应)。因此，亚致癌的BaP和UVA的结合增强了启动和促进活性，从而导致了协同致癌作用。为了验证这一假设，本文提出了四个具体目标。最初的目的是确定UVA和BaP是否协同增强皮肤癌的发生。将BaP局部应用于无毛小鼠背部皮肤或口服，然后再进行UVA照射。记录潜伏期、肿瘤发生率和复数，以评价其协同作用。第二个目的是阐明体内协同作用的机制。我们将确定BaP的应用是否增强了UVA照射的小鼠皮肤和肿瘤组织中氧化剂、氧化DNA碱基和大量DNA加合物的形成，原癌基因的表达，以及ms癌基因和p53抑癌基因的突变。第三个目的是研究体外协同作用的分子机制。利用小鼠和人角质形成细胞研究BaP调节UVA诱导的DNA氧化损伤、表皮生长因子受体的磷酸化以及酪氨酸蛋白激酶和丝裂原活化蛋白激酶的激活的机制。最后，我们将检验局部应用超氧化物歧化酶仿生剂是否能抑制氧化剂的生成、DNA氧化以及BaP-UVA对皮肤致瘤性的影响。BAP联合UVA促进DNA氧化损伤和皮肤癌变的干预将证实ROS的重要作用，并有助于我们阐明长波紫外线和BaP协同作用的分子机制。

Sunlight exposure and polycyclic aromatic hydrocarbons (PAHs) have been implicated in human skin cancers. It is assumed that excess exposure to long wavelength ultraviolet A (UVA) combined with PAHs from cigarette smoking or environmental pollution may be associated with the alarmingly increased skin cancers. The central hypothesis of this proposal is that a wide-spread environmental pollutant benzo(a)pyrene (BaP) serves as a photosensitizer to generate reactive oxygen species (ROS) upon UVA inadiation. ROS preduced by BaP-UVA treatment induce oxidative DNA damage, enhance the BaP-DNA adduct fonnation (genetic effect) as well as activate the signal transduction cascades (epigenetic effects). Thus, combination of subcaminogenic BaP and UVA potentiates both initiating and promoting activities, and subsequently leads to synergistic carcinogenicity. To test the established hypothesis, four specific aims have been proposed. The initial aim is to determine if UVA and BaP synergistically enhance skin carcinogenesis. BaP will be topically applied to dorsal skin of hairless mice or orally administered, then followed by UVA irradiation. The latent period, tumor incidence and multiplicity will be recorded to evaluate the synergetic action. The second aim is to elucidate the mechanisms of synergistic action in vivo. We will determine if application of BaP potentiates the formation of oxidants, oxidized DNA bases and bulky DNA adducts, expression of protooncogenes, and mutation of ms oncogenes and p53 tumor suppressor genes in UVA-irradiated mouse skin and tumor tissues. The third aim is to characterize molecular mechanisms of synergetic action in vitro. Murine and human keratinocytes will be used to investigate the mechanisms by which BaP modulates UVA-induced oxidative DNA damage, phosphorylation of epidermal growth factor receptor and activation of tyrosine protein kinases and mitogen-activated protein kinases. Finally, we will examine if topical application of a SOD biomimetic inhibits oxidant generation, DNA oxidation as well as skin tumorigenicity by BaP-UVA. Intervention of BaP plus UVA-enhanced oxidative DNA damage and skin carcinogenesis will confirm the important role of ROS and help us elucidate the molecular mechanisms of synergetic action of long wavelength UV light and BaP.