Biomedical Science Program, Faculty of Graduate School, Chulalongkorn University, Bangkok, Thailand.
Hum Genet. 2013 Dec;132(12):1383-93. doi: 10.1007/s00439-013-1345-9. Epub 2013 Aug 8.
Two syndromic cognitive impairment disorders have very similar craniofacial dysmorphisms. One is caused by mutations of SATB2, a transcription regulator and the other by heterozygous mutations leading to premature stop codons in UPF3B, encoding a member of the nonsense-mediated mRNA decay complex. Here we demonstrate that the products of these two causative genes function in the same pathway. We show that the SATB2 nonsense mutation in our patient leads to a truncated protein that localizes to the nucleus, forms a dimer with wild-type SATB2 and interferes with its normal activity. This suggests that the SATB2 nonsense mutation has a dominant negative effect. The patient's leukocytes had significantly decreased UPF3B mRNA compared to controls. This effect was replicated both in vitro, where siRNA knockdown of SATB2 in HEK293 cells resulted in decreased UPF3B expression, and in vivo, where embryonic tissue of Satb2 knockout mice showed significantly decreased Upf3b expression. Furthermore, chromatin immunoprecipitation demonstrates that SATB2 binds to the UPF3B promoter, and a luciferase reporter assay confirmed that SATB2 expression significantly activates gene transcription using the UPF3B promoter. These findings indicate that SATB2 activates UPF3B expression through binding to its promoter. This study emphasizes the value of recognizing disorders with similar clinical phenotypes to explore underlying mechanisms of genetic interaction.
两种综合征认知障碍疾病具有非常相似的颅面畸形。一种是由 SATB2 基因突变引起的，SATB2 是一种转录调节剂；另一种是由杂合突变导致 UPF3B 提前出现终止密码子引起的，UPF3B 编码无意义介导的 mRNA 降解复合物的一个成员。在这里，我们证明这两种致病基因的产物在相同的途径中起作用。我们表明，我们患者中的 SATB2 无义突变导致截短的蛋白定位到核内，与野生型 SATB2 形成二聚体并干扰其正常活性。这表明 SATB2 无义突变具有显性负效应。与对照组相比，患者的白细胞中 UPF3B mRNA 显著减少。这种效应在体外通过 SATB2 在 HEK293 细胞中的 siRNA 敲低导致 UPF3B 表达减少得到复制，并且在体内，Satb2 敲除小鼠的胚胎组织中 Upf3b 表达显著减少得到复制。此外，染色质免疫沉淀表明 SATB2 结合到 UPF3B 启动子上，而荧光素酶报告基因测定证实 SATB2 表达通过结合到其启动子显著激活基因转录。这些发现表明 SATB2 通过结合其启动子激活 UPF3B 的表达。这项研究强调了认识具有相似临床表型的疾病以探索遗传相互作用的潜在机制的价值。
