REGULATION BY CELL SURFACE RECEPTOR ADP-RIBOSYLATION

该项目的总体目标是研究限制炎症T细胞，特别是细胞毒性T细胞（CTL）功能的调节机制。我们将检验从裂解细胞释放的成分可能通过为存在于T细胞上的外泌酶提供底物而参与T细胞调节的假设。在可能的底物中，NAD是细胞内含量丰富但细胞外浓度极低的一种。支持NAD可能在CTL功能中发挥调节作用的观点是，存在分裂NAD的酶，导致蛋白质中精氨酸的翻译后修饰，称为单adp核糖基化。同时发现多种CTL功能受到抑制。我们打算探索淋巴细胞表面分子的单adp核糖基化如何调节其功能。细胞表面ADP-核糖基转移酶（ADPRT）在淋巴细胞类别上的表达将被检测并与NAD的抑制作用相关。为了阐明这种调控回路的确切机制，我们提出了实验来鉴定被修饰的细胞表面蛋白。初步实验表明，这种修饰会影响共受体，从而导致T细胞受体信号传导的抑制。鉴于受体相互关联以传递激活信号的必要性，本文描述了支持这一假设的具体方法。

The overall goal of this project is to examine a regulatory mechanisms that limits the function of inflammatory T cells, specifically cytotoxic T cells (CTL). The hypothesis will be examined that components released from lysing cells may be involved in T cell regulation by providing a substrate for an ecto-enzyme present on T cells. Among the possible substrates, NAD is one which is abundant inside cells but its extracellular concentration is exceedingly low. Support for the notion that NAD may play a regulatory role in CTL function is the presence of enzymes that split NAD leading to a posttranslational modification of arginines in proteins, known as mono-ADP-ribosylation. Concomitantly various CTL functions are found to be inhibited. We propose to explore how mono-ADP-ribosylation of cell surface molecules on lymphocytes, regulates their function. The expression of cell surface ADP- ribosyltransferase (ADPRT) on lymphocyte classes will be assayed and correlated with inhibitory effects of NAD. To elucidate the precise mechanisms responsible for this regulatory circuit, experiments are proposed to identify the cell surface proteins which are modified. Preliminary experiments suggest that the modification affects co- receptors and that this causes inhibition of T cell receptor signaling. Approaches are described to support this hypothesis specifically in view of the necessity for receptors to associate with each other in order to transmit activation signals.