PRECANCEROUS EVENTS IN CLINICALLY NORMAL SKIN

阳光至少在人类皮肤癌中扮演了一个有据可查的角色： 突变基因如TP53和PTCH。一个TP53突变使 抗细胞凋亡。本项目以下列迹象为基础 阳光还有第二个功能--迫使突变的细胞克隆 扩展成癌前病变。我们的工作假设是：i)正常皮肤 包含在肿瘤抑制基因中突变的细胞的小克隆。Ii) 这些克隆处于克隆扩展和克隆扩展之间的平衡状态 回归。III)抗凋亡细胞的克隆性扩张被驱动 通过阳光诱导周围正常细胞的凋亡。回归 是由细胞凋亡或免疫机制驱动的。四)这些细胞级别 事件极大地影响了积累连续 基因改变。因为皮肤癌是如此频繁，超过了所有 其他癌症合并在美国南部和夏威夷，潮起潮落 在外表正常的皮肤中，突变克隆似乎是一种常见的事件。 最近的技术进步使这种克隆可以在 光学或共聚焦显微镜，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 大小反映了克隆的扩张过程。在标识克隆之后 免疫组织化学显示，可以对其进行显微解剖以进行DNA测序或 双重标记来研究另一个基因。正常人的日照皮肤 个体通常包含数千个突变的TP53克隆。 并不是所有的克隆都需要由阳光产生。的先例 花斑病和相关的马赛克皮肤病使我们假设 在胚胎发育过程中，肿瘤抑制基因也会发生突变。成年人 患者将有一个限定的皮肤区域，其上有多个 癌症就会发展。 因此，人类和小鼠将被用来研究细胞克隆 外观正常的皮肤中的肿瘤抑制基因突变。首先，我们 研究克隆动力学：UVB和UVA是否增加了克隆的大小和 TP53突变克隆或光化性角化病的频率，无论是防晒霜 安全地反对或加剧这个过程，无论褐黑素是一种 在UVA作用中的关键因素，以及是否自发消退 TP53-突变克隆和光化性角化病是由于免疫或 细胞凋亡机制。第二，我们研究克隆结构：确定 TP53-突变克隆的功能特性及PTCH-突变的鉴定 克隆及其在克隆扩增中的作用和鉴定 基底细胞癌患者存在PTCH嵌合突变。

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.