PRECANCEROUS EVENTS IN CLINICALLY NORMAL SKIN

阳光在人类皮肤癌中至少有一个被充分证明的作用： 突变基因如TP 53和PTCH。 TP 53突变导致 抗衰老 本项目的依据是， 阳光还有第二个功能--迫使突变细胞克隆 扩展成癌前病变 我们的工作假设是：i）正常皮肤 含有肿瘤抑制基因突变的细胞的小克隆。ii）第二阶段 这些克隆存在于克隆扩张和 回归分析iii）驱动抗凋亡细胞的克隆扩增 通过阳光诱导周围正常细胞的凋亡。 回归 是由凋亡或免疫机制驱动的。（四）细胞水平 事件显著影响累积连续的 基因改变 因为皮肤癌是如此频繁，超过所有 美国南部和夏威夷的其他癌症， 突变克隆体的出现似乎是正常外观皮肤的常见事件。 最近的技术进步使这种克隆直接观察下， 光或共聚焦显微镜，就像培养皿上的细菌菌落。 克隆的数量表示突变的频率;克隆的 大小反映了克隆扩展过程。在克隆被识别之后 在化学上，它可以被显微切割用于DNA测序， 双标记来研究另一个基因。 暴露在阳光下的皮肤 个体通常含有数千个TP 53突变的克隆。 不是所有的克隆都需要阳光。 的先例 斑驳病和相关的马赛克皮肤病使我们假设， 肿瘤抑制基因也可以在胚胎发生期间发生突变。 成人 然后，患者将具有皮肤的限定区域， 癌症发展。 因此，人类和小鼠将用于研究具有以下特征的细胞克隆： 外观正常的皮肤中的肿瘤抑制基因突变。一是 研究克隆动力学：UVB和UVA是否会增加大小， TP 53突变克隆或光化性角化病的频率，无论是防晒霜 安全地对抗这一过程或加剧它，无论是褐黑素是一种 UVA作用的关键因素，以及是否自发消退 TP 53突变克隆和光化性角化病是由于免疫或 凋亡机制其次，我们研究克隆结构： TP 53突变体克隆的功能特性，鉴定PTCH突变体 克隆和TP 53在其克隆扩增中的作用，并鉴定 在PTCH中具有嵌合突变的基底细胞癌患者。

Sunlight has at least one well-documented role in human skin cancer: mutating genes such as TP53 and PTCH. A TP53 mutation confers apoptosis-resistance. The present project is based on indications that sunlight has a second function -- forcing mutated cells to clonally expand into a precancer. Our working hypothesis is that: i) Normal skin contains small clones of cells mutated in a tumor suppressor gene. ii) These clones exist in equilibrium between clonal expansion and regression. iii) Clonal expansion of apoptosis-resistant cells is driven by sunlight-induced apoptosis of surrounding normal cells. Regression is driven by apoptotic or immunologic mechanisms. iv) These cell-level events significantly affect the time needed to accumulate successive gene alterations. Because skin cancer is so frequent, surpassing all other cancers combined in the southern U.S. and Hawaii, the ebb and flow of mutant clones appears to be a common event in normal-appearing skin. Recent technical advances make such clones directly observable under the light- or confocal microscope, like bacterial colonies on a petri dish. The number of clones indicates the frequency of mutations; a clone's size reflects clone-expanding processes. After a clone is identified immunohistochemically, it can be microdissected for DNA sequencing or double-labeled to study another gene. The sun-exposed skin of normal individuals often contains thousands of TP53-mutated clones. Not all clones need be generated by sunlight. The precedent of piebaldism and related mosaic skin diseases leads us to hypothesize that tumor suppressor genes can also mutate during embryogenesis. The adult patient will then have a circumscribed region of skin on which multiple cancers develop. Therefore, human and mouse will be used to study clones of cells with tumor-suppressor gene mutations in normal-appearing skin. First, we investigate clone dynamics: whether UVB and UVA increase the size and frequency of TP53-mutant clones or actinic keratoses, whether sunscreens safely oppose this process or exacerbate it, whether pheomelanin is a key factor in UVA action, and whether the spontaneous regression of TP53-mutant clones and actinic keratoses is due to an immune or apoptotic mechanism. Second, we investigate clone structure: determining functional properties of TP53-mutant clones, identifying PTCH-mutant clones and the role of TP53 in their clonal expansion, and identifying basal cell carcinoma patients having mosaic mutations in PTCH.