行政院國家科學委員會專題研究計畫成果報告:探討SEMA3, neuropilins及plexins在黑色素細胞癌侵犯過程之表現及角色

Semaphorins 為調控軸突導引之膜附型及分泌型訊號。Semaphorin 家族可分 為7 類。第1 及第2 類為無脊椎動物之semaphorin。脊椎動物semaphorin 約有 20 種，為第3 到第7 類；其中只有第3 類semaphorin 具分泌性。脊椎動物semaphorin 受器有2 種：plexin 本身可和膜附型semaphorin 結合，但plexin 需聯合neuropilin 才可認識分泌型semaphorin。至今已有9 種脊椎動物的plexin 被確認，依其結構 相似性分為A-D 4 型。Neuropilin 則有2 型：neuropilin-1 及neuropilin-2，對第3 類semaphorin 具高親合力。 Semaphorins 及plexins 原本是因調控排斥性軸突導引而被發現，和MET 分 子有演化遺傳上之相關。在結構方面，它們在細胞外皆具備一個約500 個胺基酸 組成之sema 區域及一個由8 個半胱胺酸肽鏈組成之”MET相關序列”。MET 之 活性在許多人類癌症皆有失調現象，因此越來越多的資料顯示和其結構類似之 semaphorin 及plexin 也和侵犯性腫瘤生長之調控有關。SEMA3C 已知在放射線 治療無效的再發性鱗狀細胞癌及轉移性肺腺癌呈現過量表現。SEMA3E 則表現 於轉移性細胞株，但在非轉移性親代細胞株則否。然而，SEMA3A、neuropilin-1 及plexin-A1 之自分泌路徑則發現會阻礙乳癌細胞之趨化性。現今 semaphorin/plexin 在腫瘤侵入性生長之調控所扮演之角色仍未確立。 皮膚黑色素細胞癌之特色在於腫瘤由水平生長期，垂直生長期進展到轉移性 散佈。根據semaphorin/neuropilin/plexin 系統在癌細胞發生及移動上扮演某一角 色之假設，我們對SEMA3、neuropilins 及plexins 在惡性黑色素細胞癌之表現及 其產生之生物效應相當有興趣。我們首先會全面性地篩檢 SEMA3/neuropilin/plexin 在黑色素細胞癌細胞株及外科檢體之表現。接著，藉由 AP-SEMA3 之結合及RNA 干擾作用，我們可釐清SEMA3、neuropilin、及plexin 對黑色素細胞癌侵犯性之影響。Semaphorins are membrane-bound and secretory signals that control axonal guidance. The semaphorin family is divided into seven classes. Class 1 and 2 are invertebrate semaphorins. About 20 vertebrate semaphorins have been identified. They are divided into five classes, numbered 3 to 7; only class 3 semaphorins are secreted. Two distinct types of vertebrate semaphorin receptor are known: plexin alone can bind membrane-bound semaphorins, whereas plexins that are associated with neuropilins recognize secreted semaphorins. To date, nine vertebrate plexins have been identified and divided into A, B, C, and D subfamilies based on structurally similarity. There are two types of neuropilin. Neuropilin-1 and neuropilin-2 have been identified as high-affinity binding sites for class 3 semaphorins. Semaphorins and plexins, originally identified as molecules mediating repulsive axon guidance, are phylogenetically related to MET. Structurally, all share extracellular domains containing a ～ 500 amino acid sema domain and an eight-cysteine peptide module (MET-related sequence). As MET activity is deregulated in many human cancers, data are emerging that the structurally related semaphorins and plexins are also involved in the control of invasive tumor growth. SEMA3C has been reported to be overexpressed in radiation-resistant, recurrent squamous cell carcinoma and metastatic lung adenocarcinoma. SEMA3E is expressed in metastatic cell lines but not in the non-metastatic parental population. However, an autocrine pathways involving SEMA3A, neuropilin-1, and plexin-A1 impedes the chemotaxis of breast carcinoma cells. To date, a causal role for semaphorins/plexins in the regulation of neoplastic invasive growth has not been well established. Cutaneous melanoma is characterized by the progression through a radial growth phase, a vertical growth phase, and then metastatic spread. Given the putative role of the semaphorin/neuropilin/plexin system in cancer development and migration, we are interested to investigate the expression and the biological effects of SEMA3, neuropilins, and plexins in malignant melanoma. We will first globally screen the expression of SEMA3/neuropilins/plexins expression in melanoma cell lines and surgical melanoma specimens. Thereafter, after applying AP-SEMA3 binding ligand or RNAi to melanoma cells, the consequence of cell invasion will be evaluated