The role of keratinocyte p53 in development of pigmented lesions

 描述（由申请人提供）：皮肤恶性黑色素瘤是最致命的皮肤癌。日光中的紫外线辐射（UVR）在黑色素瘤发展中起致病作用，既作为引发剂，通过突变激活癌基因如BRAF，又作为促进剂，通过影响黑素细胞迁移和增殖。虽然强烈的紫外线辐射导致晒伤与黑色素瘤风险有关，但流行病学表明，持续的低水平慢性暴露可能会预防黑色素瘤。该建议的重点是转录因子p53，基因组和细胞应激的传感器，其在UVR后角质形成细胞中的作用。紫外线照射激活角质形成细胞中的p53，并根据损伤的水平或类型，诱导角质形成细胞凋亡（晒伤细胞），并增加黑素细胞生长因子的表达，如KIT配体（KITLG），控制黑素细胞增殖和功能;因此p53可能很好地调节黑色素瘤风险。事实上，在我们的煤烟足共济失调（SFA）小鼠与组成性高p53水平的角质形成细胞，我们观察到角质形成细胞衍生的黑素细胞生长因子的表达增加和黑素细胞数量增加。重要的是，这些小鼠在进行致癌实验时会发生痣和黑色素瘤。这些数据强烈表明角质形成细胞p53的肿瘤促进作用。最近，我们在KITLG基因座的p53反式激活位点中鉴定了一个关键的人类癌症风险SNP，该SNP导致UVR后KITLG表达增加。总之，这些数据使我们假设，角质形成细胞中的强p53激活刺激了生长因子丰富的环境，促进了色素性病变的发生和发展为黑色素瘤;而持续的低p53激活保护了黑色素瘤的发展。将使用我们的组成型角质形成细胞p53过表达SFA小鼠和我们的强力霉素诱导的Tet-ON角质形成细胞p53过表达小鼠来测试p53的这种新作用。在目的1中，我们将研究角质形成细胞中p53激活对旁分泌因子释放和黑素细胞增殖的影响。p53通路活性的详细分析，包括监管机构和靶基因，在不同水平的p53的存在下，将使我们能够构建一个模型的p53作用在角质形成细胞，可以解释急性强烈的紫外线和黑色素瘤的风险之间的明显联系和协会的慢性低紫外线与黑色素瘤的保护。在目标2中，我们将使用我们的Tet-ON p53小鼠与BrafV 600 E黑色素瘤小鼠模型组合来研究角质形成细胞中不同水平的p53活化对痣和黑色素瘤发展的旁分泌作用。我们将研究急性强烈的p53激活作为黑色素瘤的启动子，和低慢性p53激活作为对紫外线诱导的黑色素瘤的保护介质。 这一建议将产生更多的了解p53信号在角质形成细胞和黑色素细胞和黑色素瘤的影响，可能最终导致新的战略，黑色素瘤的化学预防。本建议书中生成的数据将用于支持研究这些策略的R 01应用程序。

 DESCRIPTION (provided by applicant): Cutaneous malignant melanoma is the deadliest form of skin cancer. Ultraviolet radiation (UVR) in sunlight plays a causative role in melanoma development both as an initiator, through mutational activation of oncogenes such as BRAF, and as a promoter through effects on melanocyte migration and proliferation. While intense UVR resulting in sunburns is associated with melanoma risk, epidemiology shows that persistent lower level chronic exposure may protect against melanoma. This proposal focuses on the transcription factor p53, a sensor of genomic and cellular stress, and its action in keratinocytes after UVR. UVR activates p53 in keratinocytes, and depending on the level or type of damage, induces keratinocyte apoptosis (sunburn cells), and increases the expression of melanocyte growth factors, like KIT Ligand (KITLG), that control melanocyte proliferation and function; therefore p53 may well modulate melanoma risk. Indeed, in our Sooty Foot Ataxia (SFA) mice with constitutively high p53 levels in keratinocytes, we observed increased expression of keratinocyte-derived melanocyte growth factors and elevated melanocyte numbers. Importantly, these mice develop nevi and melanomas when subjected to a carcinogenesis protocol. These data strongly suggest a tumor promotional role for keratinocyte p53. Recently, we identified a key human cancer risk SNP in the p53 transactivation site at the KITLG locus that resulted in increased KITLG expression post-UVR. Together these data led us to hypothesize that strong p53 activation in keratinocytes stimulates a growth factor-rich environment that promotes the initiation and progression of pigmented lesions to melanoma; whereas persistent low p53 activation protects against melanoma development. This new role for p53 will be tested using both our constitutive keratinocyte p53 overexpressing SFA mice and our Doxycycline-inducible Tet-ON keratinocyte p53 overexpressing mice. In Aim 1, we will examine the impact of p53 activation in keratinocytes on the release of paracrine factors and on melanocyte proliferation. A detailed analysis of p53 pathway activity, including regulators and target genes, in the presence of different levels of p53 will allow us to construct a model of p53 action in keratinocytes that may explain the apparent link between acute intense UVR and melanoma risk and the association of chronic low UVR with protection from melanoma. In Aim 2, we will use our Tet-ON p53 mice in combination with the BrafV600E melanoma mouse model to study the paracrine effects of different levels of p53 activation in keratinocytes on nevus and melanoma development. We will investigate both acute intense p53 activation as a melanoma promoter, and low chronic p53 activation as a mediator of protection against UVR-induced melanoma. This proposal will yield a greater understanding of p53 signaling in keratinocytes and its impact on melanocytes and melanoma that may ultimately lead to new strategies for melanoma chemoprevention. The data generated in this proposal will be used to support an R01 application investigating these strategies.