Function of PAP-1,a causative gene for retinitis pigmentosa

pap1是Pim1癌基因的磷酸化靶点，最近被认为是一种常染色体显性视网膜色素变性（adRP）的RP9的缺陷基因。然而，RP9是一种罕见的疾病，只描述了两种错义突变，因此PAP-1与RP9之间的联系的报道是试探性的。PAP-1在细胞中的确切作用在当时也是未知的。我们现在报道，PAP-1定位于含有剪接因子SC35的核斑点中，并直接与另一个剪接因子U2AF35相互作用。此外，我们使用体内剪接实验表明，PAP-1具有改变前mrna剪接模式的活性，并且这种活性依赖于PAP-1的磷酸化状态。我们使用相同的剪接实验来检测RP9患者中发现的两种突变形式的PAP-1的活性。结果表明，与野生型PAP-1相比，其中一个突变H137L对剪接活性没有影响，而另一个突变D170G则导致剪接活性缺陷和磷酸化PAP-1比例降低。因此，D17OG突变可能通过减少PAP-1磷酸化改变视网膜基因的剪接而导致RP。这些结果表明，PAP-1在mrna前剪接中起作用，并且考虑到其他三种剪接因子与adRP有关，这一发现提供了令人信服的进一步证据，证明PAP-1确实是RP9基因。

PAP-1, a phosphorylation target of the Pim1 oncogene, has recently been implicated as the defective gene in RP9, one type of autosomal dominant retinitis pigmentosa (adRP). However, RP9 is a rare disease and only two missense mutations have been described, so the report of a link between PAP-1 and RP9 was tentative. The precise cellular role of PAP-1 was also unknown at that time. We now report that PAP-1 localizes in nuclear speckles containing the splicing factor SC35 and interacts directly with another splicing factor, U2AF35. Furthermore we used an in vivo splicing assay to show that PAP-1 has an activity which alters the pattern of pre-mRNA splicing and that this activity is dependent on the phosphorylation state of PAP-1. We used the same splicing assay to examine the activities of two mutant forms of PAP-1 found in RP9 patients. The results showed that while one of the mutations, H137L, had no effect on splicing activity compared with that of wild-type PAP-1, the other, D170G, resulted in both a defect in splicing activity and a decreased proportion of phosphorylated PAP-1. The D17OG mutation may therefore cause RP by altering splicing of retinal genes through a decrease in PAP-1 phosphorylation These results demonstrate that PAP-1 has a role in pre-mRNA splicing and, given that three other splicing factors have been implicated in adRP, this finding provides compelling further evidence that PAP-1 is indeed the RP9 gene.