SSBP3 Interacts With Islet-1 and Ldb1 to Impact Pancreatic β-Cell Target Genes
SSBP3 Interacts With Islet-1 and Ldb1 to Impact Pancreatic β-Cell Target Genes
复制标题
DOI：
10.1210/me.2015-1165
复制
发表时间：
2015-12-01
影响因子：
--
通讯作者：
Hunter, Chad S.
中科院分区：
文献类型：
--
作者：
Galloway, Jamie R.;Bethea, Maigen;Hunter, Chad S.
islet -1 （Isl1）是一种Lin11， Isl1, Mec3 （LIM）同源结构域转录因子，对胰岛细胞的发育，成熟和功能至关重要，主要需要与LIM结构域结合蛋白1 （Ldb1）共调节因子相互作用。在其他组织中，Ldb1和Isl1与其他因子相互作用介导靶基因转录，但在β细胞中已知的蛋白伴侣很少。因此，我们假设Ldb1和Isl1参与了更大的调控复合物来影响β细胞基因表达。为了验证这一点，我们使用交联免疫沉淀和质谱法从小鼠β细胞中鉴定相互作用的蛋白质。蛋白质组学数据集揭示了许多相互作用的候选者，包括单链dna结合蛋白（SSBP）共调节家族的成员SSBP3。ssbp在其他组织中增强LIM转录因子复合物的活性和稳定性。然而，对β细胞中SSBP3的相互作用、表达或活性一无所知。我们的分析证实，在β细胞系、小鼠和人胰岛中，SSBP3与Ldb1和Isl1相互作用，并证实SSBP3与Ldb1和Isl1胰腺组织共表达。此外，β细胞系SSBP3敲低导致mRNA缺乏，与体外或体内Ldb1减少时观察到的相似。这似乎（至少）是由于SSBP3占据了已知的Ldb1-Isl1靶启动子，包括MafA和Glp1r。本研究共同证明SSBP3是Ldb1-Isl1调控复合物的关键组分，是关键β细胞靶基因表达所必需的。
Islet-1 (Isl1) is a Lin11, Isl1, Mec3 (LIM)-homeodomain transcription factor important for pancreatic islet cell development, maturation, and function, which largely requires interaction with the LIM domain-binding protein 1 (Ldb1) coregulator. In other tissues, Ldb1 and Isl1 interact with additional factors to mediate target gene transcription, yet few protein partners are known in beta-cells. Therefore, we hypothesize that Ldb1 and Isl1 participate in larger regulatory complexes to impact beta-cell gene expression. To test this, we used cross-linked immunoprecipitation and mass spectrometry to identify interacting proteins from mouse beta-cells. Proteomic datasets revealed numerous interacting candidates, including a member of the single-stranded DNA-binding protein (SSBP) coregulator family, SSBP3. SSBPs potentiate LIM transcription factor complex activity and stability in other tissues. However, nothing was known of SSBP3 interaction, expression, or activity in beta-cells. Our analyses confirmed that SSBP3 interacts with Ldb1 and Isl1 in beta-cell lines and in mouse and human islets and demonstrated SSBP3 coexpression with Ldb1 and Isl1 pancreas tissue. Furthermore, beta-cell line SSBP3 knockdown imparted mRNA deficiencies similar to those observed upon Ldb1 reduction in vitro or in vivo. This appears to be (at least) due to SSBP3 occupancy of known Ldb1-Isl1 target promoters, including MafA and Glp1r. This study collectively demonstrates that SSBP3 is a critical component of Ldb1-Isl1 regulatory complexes, required for expression of critical beta-cell target genes.