Plexin signalling in melanocyte biology and melanoma progression

描述(申请人提供)：人类黑素细胞是一种来源于神经脊部的细胞，在皮肤中执行独特的功能。虽然它们是表皮中的一小部分，但它们负责通过产生黑色素并将其转移到角质形成细胞来保护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，黑色素瘤是从良性到微侵袭，再到转移性肿瘤的一步一步的进展[2]。旁分泌因子主要由角质形成细胞产生，也由成纤维细胞产生，控制多种黑素细胞的功能，包括树突、迁移、生长和色素沉积，也调节皮肤中黑素细胞的正常动态平衡。这些生长因子及其受体或信号通路的紊乱与黑色素瘤的进展以及色素沉着的紊乱有关[3]。因此，发现新的或新的旁分泌因子，并确定这些因子刺激的受体和信号通路，对于了解皮肤中黑素细胞的调节和黑色素瘤的进展具有重要意义。信号素是最初在神经系统中发现的一大类蛋白质，是轴突引导的关键调节因子。在过去的5年里，大量的报道表明信号素及其受体(神经丛蛋白和神经粘连蛋白)广泛分布，并调节多种生物过程，包括细胞黏附和迁移、轴突伸展、免疫功能、器官发生和肿瘤进展。我们已发表的和初步的数据显示，信号素在人类黑素细胞功能中的作用以前未被认识到。信号素4D和信号素7A调节其他细胞类型的多种细胞过程，包括轴突生长和收缩、肿瘤进展和免疫调节[4]。我们首次证明信号素4D(Sema4D)和信号素7A(Sema7A)控制黑素细胞的附着、扩散和树突，这对正常皮肤色素沉积至关重要。此外，我们的数据表明Sema4D和Sema7A在黑色素瘤进展中可能起到作用，因为它们的同源受体(分别为丛状蛋白B1和丛状蛋白C1)在黑色素瘤中要么减少，要么缺失。最后，我们的初步数据表明，Sema4D在下调c-Met受体激活方面发挥了新的作用，c-Met受体是一种对黑素细胞生长、迁移、分化和黑色素瘤进展至关重要的受体。我们假设Sema4D和Sema7A通过刺激细胞内信号通路来调节黑素细胞的迁移和树突的形成，这些信号通路包括GTP结合蛋白Ras、Rho、Rac、整合素和Lim激酶-cofilin通路。我们预测，Sema7A的作用是通过1-整合素和cofilin激活之间的平衡来调节的。我们预测Sema4D的作用是通过c-Met受体抑制和Plexin B1激活之间的平衡来实现的。最后，我们预测，由于c-Met受体抑制的丧失和coflin的激活，Plexin B1和Plexin C1的表达缺失分别通过促进黑色素瘤细胞的生长、迁移和存活而促进了黑色素瘤的进展。 与公共卫生相关。识别调节人类黑素细胞功能的新的生长因子对于了解皮肤的色素沉着以及在良性黑素细胞向恶性黑色素瘤的转化过程中具有重要意义。我们已经鉴定出两种蛋白质，Semaphorin 4D和Semaphorin 7A，它们分别通过受体Plexin B1和Plexin C1刺激人类黑素细胞的功能。此外，我们发现这两种受体在黑色素瘤细胞系中都减少或缺失，在体内的黑色素瘤中，就Plexin C1而言，也是如此。这个项目的目标是确定信号素是如何通过丛状受体传递信号的，并了解丛状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.