Role of alpha6beta4 integrin in epidermal carcinogenesis

描述(申请人提供)：鳞状细胞癌(SCC)约占所有非黑色素瘤皮肤癌的20%，这是人类最常见的恶性肿瘤类型。皮肤鳞状细胞癌具有较高的侵袭和转移倾向，但其侵袭行为的生物学基础尚不清楚。鳞状细胞癌等上皮性肿瘤的一个特征是不适当地表达α6β4整合素，这是肿瘤进展的高风险。然而，在其他正常的上皮细胞中，α6β4的异常表达对疾病的发生和进程的影响还相对未知。Alpha6beta4的超基础表达使表皮易于形成化学诱导的肿瘤，并通过一种需要E-钙粘素介导的细胞间黏附和PI 3-激酶活性的机制干扰基底细胞中的转化生长因子β(TGFbeta)信号转导。该提案的目的是确定超基础α6β4表达可促进表皮肿瘤形成和干扰TGFβ信号的分子事件。Rho家族的小GTP酶介导肌动蛋白细胞骨架的重组，并与上皮性肿瘤的进展有关。初步研究结果表明，超基础α6beta4与肌动蛋白细胞骨架相连，并与rac1共定位，在表现出超基础α6beta4表达的转基因小鼠表皮和人类SCC中，Rac的激活发生了改变。为了设想一种方法，即α6β4整合素、E-钙粘蛋白和PI 3-激酶可以共同作用于调控TGFbeta信号和表皮肿瘤的形成，本提案的目的将集中在Rho家族小GTP酶的作用上。 我们将研究Rho GTP酶在转基因小鼠表皮和表现出超基础α6β4表达的人干细胞中的表达和活性的变化。我们将在高表达α6beta4的细胞中操纵Rho GTPase和PI 3-Kinase信号，并确定其对TGFbeta介导的生长抑制的影响。为了明确Rho GTP酶活性在表皮肿瘤形成中的作用，我们将产生缺乏Rho GTP酶活性并表现出超基础α6β4表达的转基因小鼠表皮。在这个模型中，我们将测量消融的Rho GTPase信号对基底细胞增殖和SCC诱导的影响。总体而言，我们计划确定表皮皮肤细胞相互沟通方式的变化如何影响潜在致命人类皮肤癌的发展。这些研究将阐明细胞系统中对正常功能至关重要的异常如何强烈影响肿瘤的易感性，因此将对整个上皮癌领域产生广泛的影响。

DESCRIPTION (provided by applicant): Squamous cell carcinoma (SCC) constitutes approximately 20% of all nonmelanoma skin cancer, which is the most common type of human malignancy. SCC has a relatively high propensity for invasion and metastasis although the biological basis for the aggressive behavior of cutaneous SCCs is poorly understood. One characteristic of epithelial tumors such as SCC with a high risk of tumor progression is inappropriate alpha6beta4 integrin expression. However, the impact of aberrant alpha6beta4 expression in otherwise normal epithelium on the initiation and course of the disease is relatively unknown. Suprabasal expression of alpha6beta4 predisposes the epidermis to form chemically-induced tumors and perturbs transforming growth factor beta (TGFbeta) signaling in basal cells via a mechanism that requires E-cadherin-mediated intercellular adhesion and PI 3-kinase activity. The goal of this proposal is to define the molecular events by which suprabasal alpha6beta4 expression can enhance epidermal tumor formation and disrupt TGFbeta signaling. Proteins of the Rho family of small GTPases mediate actin cytoskeleton reorganization and are implicated in epithelial tumor progression. Preliminary findings indicate that suprabasal alpha6beta4 is linked to the actin cytoskeleton and co-localizes with Rac1 and that Rac activation is altered in transgenic murine epidermis and human SCCs that exhibit suprabasal alpha6beta4 expression. To envision a way that alpha6beta4 integrin, E-cadherin and PI 3-kinase could all act in concert to manipulate TGFbeta signaling and epidermal tumor formation, the aims of this proposal will focus on the role of the Rho family of small GTPases. We will characterize changes in Rho GTPase expression and activity in transgenic murine epidermis and human SCCs exhibiting suprabasal alpha6beta4 expression. We will manipulate Rho GTPase and PI 3-kinase signaling in cells overexpressing alpha6beta4 and determine its impact on TGFbeta-mediated growth inhibition. To define the effect of Rho GTPase activity on epidermal tumor formation, we will generate transgenic murine epidermis that is deficient in Rho GTPase activity and exhibits suprabasal alpha6beta4 expression. In this model we will measure the effect of ablated Rho GTPase signaling on basal cell proliferation and SCC induction. Overall, we plan to ascertain how changes in the way epidermal skin cells communicate with one another can impact on the development of potentially fatal human skin cancers. These studies will illustrate how aberrations in a cellular system essential for normal function can strongly influence the susceptibility for neoplasia, and therefore will have broad implications for the entire field of epithelial cancer.