• 作者： 朱堂元; Peter Besmer
• 作者服務機構： 國防醫學院婦產學科暨三軍總醫院婦產部; Program of Molecular Biology Memorial Sloan-Kettering Cancer Center
• 中文摘要： 在以往的研究中我們發現了原型腫瘤基因c-kit表達一種具有酪胺酸磷酸化（tyrosine kinase）功能之受體。此受體及其結合物（stem cell growth factor）所形成之訊息傳遞系統主導造血細胞、黑色素細胞及生殖細胞的生長、分化。c-kit基因在胚胎時期及成體表達的時間、位置也與此三種細胞之生長分化過程相吻合。而令人關心的問題是：c-kit基因如何適時適地在特定的細胞內表達？研究此基因調控機轉的第一步在瞭解其啟動子（promoter）。在先前的研究中，我們已分析出c-kit基因的結構，並知c-kit是由21個exons所組成。其中第一個exon代表了c-kit的5' untranslated region及蛋白質N端之signal peptide。本研究的目地在找出c-kit基因轉錄的啟始點（transcription-initiation site）及決定其啟動子的性質。我們用primer extension及S1 mapping等方法找到了一處單一啟始點。再分析啟始點上游約2500 bp之DNA序列。我們發現它缺少一般啟動子常見之TATA box，但具有數處可能與轉錄因子SP-1、GATA-1 factor、Oct-4及myb等結合之序列元（cis-elements）。為了更進一步確定此轉錄促體之功能，我們將不同片段之上游序列連接到CAT基因，送入不同的細胞內，分別觀察其促使CAT基因轉錄之能力。結果發現：自c-kit基因啟始點到其上游2700 bp長之DNA片段可以促使CAT基因在多種細胞內表達。而上游2700到5000 bp之片段則有抑制CAT基因表達之功能。本研究顯示，c-kit基因具有一獨特之啟動子。在其不同位置中分別有具活化及抑制性質之序列元存在。
• 英文摘要： In previous studies, we have characterized the nature and function of the proto-oncogene c-kit,which encodes a receptor tyrosine kinase. This receptor together with its ligand, a stem cell growth factor,constitutes a cell signaling system which is crucial for the development of hematopoietic, melanocytic andgerm cells. The expression of the gene correlates with its protein functions in specific cell lineages and istemporally and spatially regulated during fetal and adult life. As a start point to study the gene regulation,we have characterized the promoter of the c-kit gene. A single transcription initiation site located 58 basesupstream of the ATG start codon has been identified. The sequence upstream to the initiation site revealsa TATA-less, non-GC rich promoter. Several potential binding sites for transcription factors pertinent toc-kit expression, such as Sp-1, GATA-1, myb and Oct-4, have been identified. Promoter activities of dif-ferent lengths of the 5’sequence have been analyzed in transient expression assay. The 2.7 kb of the 5’sequence facilitates the expression of the CAT gene in several cell lines while the sequence further upstreamfrom 2.7 to 5.0 kb shows a negative regulatory activity. This study reveals a unique promoter of the c-kitgene and provides a basis for further elucidation of the regulatory mechanism of c-kit gene expression.
• 中文關鍵字： proto-oncogene; transcription initiation; gene structure.
• 英文關鍵字： --