THE ROLE OF THE PARP GENE IN SLE SUSCEPTIBILITY

累积的证据表明，遗传易感性导致系统性红斑狼疮(SLE)的易感性。系统性红斑狼疮易感基因的搜索主要涉及在基于人群的关联研究中作为候选的功能相关基因的测试。由于正关联可能作为群体混合的产物出现，连锁分析的加入为基于物理位置的易感基因提供了更令人信服的证据。我们以前报道过SLE与染色体1q41-q42上15 cM区域连锁的证据。在这个区间内，有几个候选基因，包括PARP和HLX1，它们分别编码聚(ADP-核糖)聚合酶(PARP)和同源盒蛋白。使用基于家族的关联检验，我们最近观察到有证据表明PARP(而不是HLX1)等位基因与系统性红斑狼疮有关联(多等位基因传递不平衡检验p=0.00008)，从而提示PARP在系统性红斑狼疮易感性中起作用。以前，PARP也被认为与SLE有关，因为它在SLE患者中的活动范围低于正常范围，在SLE患者的未受影响的家庭成员中的活动范围居中，在SLE患者中它的mRNA水平降低。据报道，在SLE患者中存在DNA修复异常。这些多方面的证据使我们假设PARP是SLE的易感基因。PARP是由DNA链断裂激活的，它将ADP-核糖残基从NAD转移到核蛋白上，参与包括DNA修复在内的各种染色质功能。它被细胞凋亡过程中诱导的caspase-3特异性切割。这项建议主要使用来自SLE患者及其家庭成员的EBV转化细胞系来测试PARP的等位基因变异是否会导致功能变异来解释SLE易感性的可遗传差异。这种PARP多态是启动子内的一种简单序列重复(SSR)，因此可能影响mRNA和蛋白质的表达水平。这种多态也可能是与影响PARP活性的其他多态(S)连锁不平衡的一个标记。我们建议1)通过比较蛋白质、mRNA、启动子活性和翻译后修饰的水平来研究SLE相关等位基因纯合个体和其他等位基因个体的PARP表达，2)表征PARP活性的等位基因变化和相关的DNA修复，3)研究诱导后PARP凋亡裂解的等位基因变化，4)确定任何观察到的PARP变化的结构基础。综上所述，我们的研究将评估PARP的等位基因变异是否会导致表达、酶活性、作为底物的敏感性以及DNA修复的数量变化，这可能与SLE的易感性有关。这项研究的结果将支持(或驳斥)PARP在SLE易感性中的作用。

Cumulative evidence has suggested that genetic predisposition contributes to susceptibility to systemic lupus erythematosus (SLE). The search of SLE susceptibility genes has involved mainly testing functionally relevant genes as candidates in population-based association studies. Because positive association may occur as an artifact of population admixture, the addition of linkage analysis offers more compelling evidence for susceptibility genes based on physical locations. We previously reported evidence for linkage of SLE to a 15 cM region on chromosome 1q41-q42. Within this interval, there are several candidate genes including PARP and HLX1 which encode poly(ADP-ribose)polymerase (PARP) and a homeo box protein, respectively. Using a family-based association test, we have recently observed evidence for association of PARP (but not HLX1) alleles with SLE in 124 families containing offspring afflicted with SLE (p= 0.00008 by the multi-allele transmission-disequilibrium test), and thus suggesting a role of PARP in SLE susceptibility. Previously PARP was also implicated in SLE based on its lower than normal range of activity in SLE patients, its intermediate range of activity in unaffected family members of SLE patients, and its decreased mRNA levels in SLE patients. Abnormal DNA repair has been reported in SLE patients. These multiple lines of evidence has led us to hypothesize that PARP is an SLE susceptibility gene. PARP is activated by DNA strand breaks which transfers ADP-ribose residues from NAD to nuclear proteins involved in various chromatin functions including DNA repair. It is specifically cleaved by caspase-3 induced during apoptosis. This proposal tests whether allelic variation of PARP causes functional variation to account for heritable differences in SLE susceptibility primarily using EBV-transformed cell lines from SLE patients and their family members. This PARP polymorphism is a simple sequence repeat (SSR) within the promoter, and thus may affect levels of mRNA and protein expression. It is also likely that this polymorphism represents a marker in linkage disequilibrium with other polymorphism(s) influencing PARP activity. We propose to 1) study PARP expression in individuals homozygous for the SLE-associated allele and individuals with other alleles by comparing levels of protein, mRNA, promoter activity, and post-translational modification, 2) characterize allelic variation of PARP activity and the related DNA repair, 3) study allelic variation of apoptotic cleavage of PARP upon induction, and 4) define the structural basis of any observed variation of PARP. In summary, our proposed study will assess whether allelic variation of PARP causes quantitative variation in expression, enzyme activity, sensitivity as a substrate, and DNA repair which may contribute to SLE susceptibility. Results from this study will support (or refute) a role of PARP in SLE susceptibility.