Analysis of transcrition regulators involved in intracellular signaling

到目前为止，已经发现了许多ATF/CREB家族的转录因子。这组蛋白质包含DNA结合域，由碱性氨基酸簇和亮氨酸拉链组成，即所谓的b-Zip。在ATF/CREB家族的众多转录因子中，Cre-BP1(又称ATF-2)、ATF-a和Cre-BPA是一个亚类。这组因子与c-Jun形成同源二聚体或异源二聚体，并与CRE结合。应激激活的激酶(SAPK)如Jun氨基末端激酶(JNK)和p38使这组因子在N端转录激活域附近的位置磷酸化，并刺激它们的反式激活能力。由于包括CREB在内的一组ATF/CREB家族因子通过cAMP依赖的蛋白激酶(PKA)直接磷酸化而被激活，这两组因子与不同的信号通路PKA和SAPK通路有关。为了更全面地研究Cre-BP1基因的生理作用，我们建立了Cre-BP1、Cre-BPA和ATF-a基因敲除小鼠。Cre-BP1的小鼠零突变在出生后不久死亡，出现严重呼吸窘迫的症状，突变的肺充满了胎粪样人胎粪吸入综合征(MAS)，这是一种常见的新生儿问题。在18.5DPC时，突变胎盘中滋养层细胞的增殖减少，突变胚胎出现缺氧现象。胎盘异常可能导致氧气供应不足，继而导致呼吸困难和羊水吸入含有粪便的羊水。突变胎盘滋养层细胞中对滋养细胞增殖起重要作用的PDGF受体α基因表达水平降低。Cre-BP1缺失突变体将有助于了解MAS的发病机制和开发MAS的治疗方法。

A number of transcription factors of ATF/CREB family have been identified so far. This group of proteins contains the DNA-binding domain consisting of the cluster of basic amino acids and the leucine zipper, so-called b-zip. Among many transcription factors of ATF/CREB family, three factors, CRE-BP1 (also called ATF-2), ATF-a, and CRE-BPa forms a subgroup. This group of factors forms a homodimer or heterodimer with c-Jun, and binds to CRE.The stress-activated kinases (SAPK) such as Jun amino-terminal kinase (JNK) and p38 phosphorylates this group of factors at the sites close to the N-terminal transcriptional activation domain, and stimulate their trans-activating capacity. Since a group of factors of the ATF/CREB family including CREB are activated via direct phosphorylation by cAMP-dependent protein kinase (PKA), these two groups of factors are linked to the distinct signaling cascades, PKA and SAPK pathways.To investigate the physiological role od CRE-BP1 genefamly, we made the knockout mice of CRE-BP1, CRE-BPa, and ATF-a genes. The mouse null mutant of CRE-BP1 died shortly after birth with symptoms of severe respiratory distress, and that the mutant lung was filled with meconium like human meconium aspiration syndrome (MAS) which is a common neonatal problem. The decreased trophobalst proliferation in the mutant placenta and the occurrence of hypoxia in the mutant embryos were observed at 18.5 dpc. Anomalies in placenta may cause the insufficient oxgen supply followed by gasping respirations and aspiration of the amniotic fluid containing meconium. The expression level of PDGF receptor alpha gene which plays an important role for proliferation of trophoblast, was found to be decreased in the trophoblasts of mutant placenta. The CRE-BP1 null mutants will be useful to understand the mechanisms of MAS and to develop the therapy for MAS.