Signaling Pathways for UV-Induced Melanogenic Responses

描述（由申请人提供）：在人类皮肤中，表皮黑色素细胞在光保护中起着至关重要的作用，主要是由于它们能够合成黑色素。黑素细胞具有极低的增殖能力，因此它们在表皮中的存活对皮肤的光保护至关重要。然而，越来越清楚的是，皮肤癌的风险不仅仅取决于皮肤中的黑色素含量，而是取决于在暴露于紫外线辐射下，巨噬细胞维持基因组稳定性的能力，以防止恶性转化为黑色素瘤。内皮素-1 （ET-1）和α -促黑素细胞激素（α - msh）是两种受紫外线照射刺激的表皮因子。这两种因素都能使人类黑色素细胞克服紫外线诱导的G1阻滞并刺激黑色素生成。最近，我们证明ET-1和apha-MSH通过抑制细胞凋亡来提高紫外线照射黑素细胞的存活率。我们发现，在α - msh受体黑素皮质素1受体中表达功能缺失突变的培养的人类黑素细胞对紫外线辐射的杀伤易感性增加。我们将这种增加的敏感性归因于紫外线照射对DNA损伤的影响，这种损伤超出了这些细胞的修复能力，并且无法完全激活生存途径。这些突变与晒黑能力差、黑色素瘤和非黑色素瘤皮肤癌的风险增加有关，与皮肤或头发颜色无关。我们假设ET- 1和α - msh通过抑制细胞凋亡和降低uvb诱导的DNA损伤程度来促进人类黑素细胞的存活。我们建议研究ET-1和/或a-MSH限制uvb诱导的DNA损伤程度和/或提高DNA修复率的能力。我们还将确定ET-1和α - msh激活Akt/ pkb依赖性存活通路的能力。已知活化的Akt/PKB通过磷酸化和灭活其底物Bad和caspase 9，以及激活NFkB和CREB来抑制细胞凋亡。此外，我们计划阐明ET-1和/或α - msh的生存效应是否涉及转录因子Mitf的激活，Mitf通过调节ERK1/2、p38和JNK/SAPK以及CREB在uvb照射黑素细胞中的活性来上调Bcl2的表达。确定来自不同色素表型的黑素细胞对生存因子的反应能力的差异，对于评估紫外线辐射对皮肤的细胞毒性和基因毒性作用的程度具有重要意义。此外，评估a- msh和ET-1对生存影响的差异敏感性可以作为确定个体患皮肤癌，特别是黑色素瘤风险的可靠标记。

DESCRIPTION (provided by applicant): In human skin, epidermal melanocytes play a crucial role in photoprotection mainly due to their ability to synthesize melanin. Melanocytes have an extremely low proliferative capacity, thus their survival in the epidermis is crucial for cutaneous photoprotection. However, it is becoming clear that the risk for skin cancer is not simply determined by melanin content in the skin, but rather by the ability of the metanocyte to maintain genomic stability in the face of exposure to ultraviolet radiation, to prevent malignant transformation into melanoma. Endothelin-1 (ET-1) and alpha-melanocyte stimulating hormone (alpha-MSH) are two epidermal factors whose synthesis is stimulated by UV exposure. Both factors enable human melanocytes to overcome UV-induced G1 arrest and stimulate melanogenesis. Recently, we demonstrated that ET-1 and apha-MSH increase the survival of UV-irradiated melanocytes by inhibiting apoptosis. We found that cultured human melanocytes that express loss-of-function mutations in the melanocortin 1 receptor, the receptor for alpha-MSH, have increased susceptibility to killing by UVR. We attribute this increased sensitivity to UV exposure to extensive DNA damage that overwhelms the repair capacity of those cells, and to inability to fully activate survival pathways. These mutations have been associated with poor tanning ability, and increased risk for melanoma and non-melanoma skin cancers, independently of skin or hair color. We hypothesize that ET- 1 and alpha-MSH promote human melanocyte survival by inhibiting apoptosis and reducing the extent of UVB-induced DNA damage. We propose to investigate the ability of ET-1 and/or a-MSH to limit the extent of UVB-induced DNA damage and/or to enhance the rate of DNA repair. We will also determine the capacity of ET-1 and alpha-MSH to activate the Akt/PKBdependent survival pathway. Activated Akt/PKB is known to inhibit apoptosis by phosphorylating and inactivating its substrates Bad and caspase 9, and by activating NFkB and CREB. Additionally, we plan to elucidate whether the survival effects of ET-1 and/or alpha-MSH involve activation of the transcription factor Mitf, which upregulates Bcl2 expression, by modulating the activities of ERK1/2, p38 and JNK/SAPK, and CREB in UVB-irradiated melanocytes. Determining the differences in the ability of melanocytes from different pigmentary phenotypes to respond to survival factors is significant for assessing the magnitude of the cytotoxic and genotoxic effects of UVR in the skin. Also, assessing the differential sensitivity to the survival effects of a-MSH and ET-1 can be used as a reliable marker for determining individual risk to skin cancer, particularly melanoma.