Plexin signalling in melanocyte biology and melanoma progression

描述（由申请人提供）：人黑素细胞是神经嵴衍生的细胞，在皮肤中执行独特的功能。虽然它们是表皮的少数群体，但它们通过产生黑色素并将其转移到角质形成细胞来负责皮肤免受紫外线辐射（UVR）的大部分光保护[1]。黑素细胞或其干细胞也是最致命的皮肤癌黑色素瘤的祖细胞，其作为从良性到微创再到转移性肿瘤的逐步进展而出现[2]。旁分泌因子主要由角质形成细胞产生，但也由成纤维细胞产生，控制多种黑素细胞功能，包括树突、迁移、生长和色素沉着，并且还调节皮肤中黑素细胞的正常稳态。这些生长因子、其受体或信号传导途径的紊乱与黑色素瘤进展以及色素沉着紊乱有关[3]。因此，发现新的或新颖的旁分泌因子，并确定受体和信号通路刺激这些因素，是重要的了解黑素细胞的调节，在皮肤和黑色素瘤肿瘤的进展。脑信号蛋白是最初在神经系统中鉴定的蛋白质的大家族，并且是轴突引导的关键调节剂。在过去的5年中，大量的研究表明，脑信号蛋白及其受体（丛蛋白和神经纤毛蛋白）广泛分布，并调节多种生物过程，包括细胞粘附和迁移，神经突起延伸，免疫功能，器官发生和肿瘤进展。我们发表的和初步的数据显示了以前未被认识到的作用，脑信号蛋白在人类黑素细胞的功能。脑信号蛋白4D和脑信号蛋白7A调节其他细胞类型中的多种细胞过程，包括神经突生长和收缩、肿瘤进展和免疫调节[4]。我们是第一个表明，semaphorin 4D（Sema 4D）和semaphorin 7A（Sema 7A）控制黑素细胞的附着，扩散和dendricity，这是至关重要的正常皮肤色素沉着。此外，我们的数据表明Sema 4D和Sema 7A在黑色素瘤进展中的潜在作用，因为它们的同源受体（分别为丛蛋白B1和丛蛋白C1）在黑色素瘤中减少或缺失。最后，我们的初步数据表明，Sema 4D在下调c-Met受体活化方面具有新的作用，c-Met受体活化是黑素细胞生长、迁移、分化和黑色素瘤进展的关键重要受体。我们假设Sema 4D和Sema 7A通过刺激包括GTP结合蛋白Ras、Rho、Rac、整联蛋白和LIM激酶- cofilin途径的细胞内信号传导途径来调节黑素细胞迁移和树突形成。我们预测Sema 7A的作用是由1-整合素和cofilin激活之间的平衡介导的。我们预测Sema 4D的作用是由c-Met受体抑制和丛蛋白B1激活之间的平衡介导的。最后，我们预测，丛蛋白B1和丛蛋白C1表达的损失有助于通过增强黑色素瘤细胞的生长，迁移和生存，由于c-Met受体抑制和coflin激活的损失，分别黑色素瘤进展。 公共卫生相关性。鉴定调节人类黑素细胞功能的新的生长因子对于理解皮肤色素沉着和良性黑素细胞向恶性黑色素瘤的转化是重要的。我们已经鉴定了两种蛋白质，Semaphorin 4D和Semaphorin 7A，它们分别通过受体丛蛋白B1和丛蛋白C1刺激人类黑素细胞功能。此外，我们表明，这两种受体在黑色素瘤细胞系中减少或不存在，并且在丛状蛋白C1的情况下，在体内黑色素瘤中。本项目的目标是确定脑信号蛋白如何通过丛状蛋白受体发出信号，并了解丛状蛋白受体表达缺失导致黑色素瘤转移的机制。

DESCRIPTION (provided by applicant): Human melanocytes are neural crest derived cells that perform a unique function in the skin. While they are a minority of the population of the epidermis, they are responsible for the majority of photoprotection of the skin from ultraviolet radiation (UVR) through the production and transfer of melanin to keratinocytes [1]. Melanocytes, or their stem cells, are also progenitor cells for the most deadly of skin cancers, melanoma, which arises as a step wise progression from benign, to minimally invasive, to metastatic tumor [2]. Paracrine factors, produced primarily by keratinocytes, but also by fibroblasts, control multiple melanocyte functions, including dendricity, migration, growth and pigmentation, and also regulate normal homeostasis of melanocytes in the skin. Disordered of these growth factors, their receptors, or signaling pathways, are implicated in melanoma progression, as well as in disordered pigmentation [3]. Therefore, discovery of new or novel paracrine factors, and defining receptors and signaling pathways stimulated by these factors, are important to understanding melanocyte regulation in the skin, and melanoma tumor progression. Semaphorins are a large family of proteins that were originally identified in the nervous system, and are critical regulators of axon guidance. During the last 5 years, numerous reports show that semaphorins and their receptors (Plexins and Neuropilins) are widely distributed and regulate multiple biologic processes, including cell adhesion and migration, neurite extension, immune function, organogenesis, and tumor progression. Our published and preliminary data show a previously unrecognized role for semaphorins in human melanocyte function. Semaphorin 4D and semaphorin 7A regulate multiple cellular processes in other cell types, including neurite outgrowth and retraction, tumor progression and immune modulation [4]. We are the first to show that semaphorin 4D (Sema4D) and semaphorin 7A (Sema7A) control melanocyte attachment, spreading and dendricity, which are critically important for normal skin pigmentation. Further, our data suggest a potential role for Sema4D and Sema7A in melanoma progression, because their cognate receptors (Plexin B1 and Plexin C1 respectively) are either reduced or absent in melanoma. Finally, our preliminary data indicate a novel role for Sema4D in downregulation of c-Met receptor activation, a receptor critically important for melanocyte cell growth, migration, differentiation, and melanoma progression. We hypothesize that Sema4D and Sema7A regulate melanocyte migration and dendrite formation through stimulation of intracellular signaling pathways that include the GTP binding proteins Ras, Rho, Rac, integrins and LIM kinase- cofilin pathways. We predict that effects of Sema7A are mediated by a balance between 1- integrin and cofilin activation. We predict that effects of Sema4D are mediated by a balance between c-Met receptor inhibition and Plexin B1 activation. Finally, we predict that loss of Plexin B1 and Plexin C1 expression contribute to melanoma progression through enhanced melanoma cell growth, migration, and survival due to loss of c-Met receptor inhibition and coflin activation, respectively. PUBLIC HEALTH RELEVANCE. Identification of new growth factors that regulate human melanocyte function is important for understanding pigmentation of the skin, and in the transformation of benign melanocytes to malignant melanoma. We have identified two proteins, Semaphorin 4D and Semaphorin 7A, which stimulate human melanocyte function through the receptors Plexin B1 and Plexin C1 respectively. Further, we show that both of these receptors are reduced or absent in melanoma cell lines, and, in the case of Plexin C1, in melanoma in vivo. The goal of this project is to define how Semaphorins signal through Plexin receptors, and to understand the mechanisms by which loss of Plexin receptor expression contributes to melanoma metastasis.