Transcriptional regulatory functions of heterogeneous nuclear ribonucleoproteim-U and -A/B in endotoxin-mediated macrophage expression of osteopontin
Transcriptional regulatory functions of heterogeneous nuclear ribonucleoproteim-U and -A/B in endotoxin-mediated macrophage expression of osteopontin
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DOI：
10.4049/jimmunol.175.1.523
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发表时间：
2005-07-01
影响因子：
4.4
通讯作者：
Kuo, PC
中科院分区：
文献类型：
--
作者：
Gao, CJ;Guo, HT;Kuo, PC
骨桥蛋白（Osteopontin，OPN）是一种由298个氨基酸组成的高亲水性、带负电荷的唾液酸蛋白，具有多种调节功能，包括细胞粘附和迁移、肿瘤生长和转移、动脉粥样硬化、主动脉瓣钙化和心肌损伤修复。OPN是一种独特的内源性NO表达负反馈抑制剂。然而，决定内毒素（LPS）和NO介导的OPN合成诱导程度的特定顺式和反式调节元件尚不清楚。我们先前已经表明，LPS诱导的异质核核糖核蛋白（hnRNP）-A/B的S-亚硝基化通过显著降低其DNA结合活性来抑制其作为OPN转录的组成型反式阻遏物的活性。hnRNP最初被描述为与RNA聚合酶II转录物形成复合物的染色质相关RNA结合蛋白。hnRNP家族由> 20种蛋白质组成，这些蛋白质有助于新生前mRNA周围的复合物，因此能够调节RNA加工。在随后的研究中，再次使用RAW 264.7海洋巨噬细胞和COS-2细胞，我们证明了hnRNP-A/B和hnRNP-U蛋白在LPS刺激的NO合成环境中对OPN表达具有拮抗性转录调节功能。在NO存在下，hnRNP-A/B从其OPN启动子位点解离，随后OPN启动子活性去抑制。随后，hnRNP-U结合到相同位点以进一步增强OPN启动子激活。这在以前对于hnRNP蛋白没有描述。我们的研究结果代表了一个独特的转录调控机制，涉及hnRNP蛋白家族成员之间的相互作用。
Osteopontin (OPN) is a highly hydrophilic and negatively charged sialoprotein of similar to 298 amino acids with diverse regulatory functions including cell adhesion and migration, tumor growth and metastasis, atherosclerosis, aortic valve calcification, and repair of myocardial injury. OPN is unique as an endogenous negative feedback inhibitor of NO expression. However, the specific cis- and trans-regulatory elements that determine the extent of endotoxin (LPS)- and NO-mediated induction of OPN synthesis are unknown. We have previously shown that LPS-induced S-nitrosylation of heterogeneous nuclear ribonucleoprotein (hnRNP)-A/B inhibits its activity as a constitutive trans-repressor of the OPN transcription by significantly decreasing its DNA binding activity. hnRNPs were originally described as chromatin-associated RNA-binding proteins that form complexes with RNA polymerase II transcripts. The hnRNP family is comprised of > 20 proteins that contribute to the complex around nascent pre-mRNA and are thus able to modulate RNA processing. In this subsequent study, again using RAW 264.7 marine macrophages and COS-2 cells, we demonstrate that hnRNP-A/B and hnRNP-U proteins serve antagonistic transcriptional regulatory functions for OPN expression in the setting of LPS-stimulated NO synthesis. In the presence of NO, hnRNP-A/B dissociates from its OPN promoter site with subsequent derepression of OPN promoter activity. Subsequently, hnRNP-U binds to the same site to further augment OPN promoter activation. This has not been previously described for the hnRNP proteins. Our results represent a unique transcriptional regulatory mechanism which involves interplay between members of the hnRNP protein family.