STRUCTURE/FUNCTION OF SURFACTANT PROTEIN D

表面活性蛋白D(SP-D)是一种胶原性碳水化合物结合蛋白，由II型和无纤毛的细支气管上皮细胞分泌到肺的空气中。SP-D与多种微生物和颗粒抗原上表达的糖偶联物结合，可调节炎性细胞的活动，也可能参与肺表面活性物质的代谢。肺损伤后SP-D的产生增加与其参与肺“急性时相反应”(APR)相一致。因此，了解调节SP-D的表达及其在空气中积累的机制是很重要的。我们的研究表明，三聚亚单位的组装和十二聚体或更大的多聚体的形成对它的许多活动是重要的--如果不是关键的话。此外，我们对人类基因的研究还发现了一个保守的AP-1元件(-109)和一个功能性的C/EBP样蛋白结合序列(-340)，它们可能有助于肺损伤后SP-D的基础表达和增加表达。相应地。我们提出了四个目标。首先，我们计划进一步鉴定近端的启动子，重点是AP-1元件两侧的保守序列，包括下游的HNF-3结合位点和上游的结合位点，其中包括重叠的E-box、GT-box和GATA样基序。其次，我们将进一步鉴定-340处的C/EBP元件和-319处的串联基序，并研究其他C/EBP基序和潜在的STAT结合序列的贡献。我们还将研究视网膜母细胞瘤蛋白和糖皮质激素对C/EBP介导的转录激活的潜在调节作用，以及IL-6和其他先前参与调节肝脏APR的细胞因子和激素的调节活性。第三，我们建议对最近发现的人类基因“内含子1”中的一个未翻译外显子进行鉴定。第四，我们建议继续研究SP-D三聚化、多聚化和分泌SP-D的机制。我们正在进行的和正在进行的研究将提供与调节SP-D的产生、功能多聚体的组装以及肺对微生物挑战和其他形式的肺损伤的反应相关的重要信息。

Surfactant Protein D (SP-D) is a collagenous carbohydrate binding protein that is secreted into the airspaces of the lung by type II and nonciliated bronchiolar epithelial cells. SP-D binds to glycoconjugates expressed on various microorganisms and particulate antigens, can modulate the activities of inflammatory cells, and may also contribute to the metabolism of lung surfactant. SP-D production increases following lung injury consistent with its participation in the pulmonary "acute phase response" (APR). For these reasons, it is important to understand the mechanisms that regulate the expression of SP-D and its accumulation in the airspace. Our studies have shown that the assembly of trimeric subunits and the formation of dodecamers or larger multimers is important- if not critical- for many of it's activities. In addition, our studies of the human gene have lead to the identification of a conserved AP-1 element (-109) and a functional C/EBP-like protein binding sequence (-340) that could contribute to basal expression and the increased expression of SP-D following lung injury. Accordingly. we propose four aims. First, we plan to further characterize the proximal promoter with emphasis on the conserved sequences that flank the AP-1 element, including a downstream HNF-3 binding site and an upstream binding site that includes overlapping E-Box, GT- box and GATA-like motifs. Second, we will further characterize the putative C/EBP element at -340 and a tandem motif at -319, and examine the contribution of other C/EBP motifs and potential STAT binding sequences. We will also examine potential modulatory effects of retinoblastoma protein and glucocorticoids on C/EBP- mediated transcriptional activation, and the regulatory activities of IL-6 and other cytokines and hormones previously implicated in the regulation of the hepatic APR. Third, we propose to characterize a recently identified untranslated exon within "intron 1" of the human gene. Fourth, we propose to continue with studies examining the mechanisms of SP-D trimerization, multimerization, and secretion of SP-D. Our ongoing and proposed studies will provide important information related to the regulation of SP-D production, the assembly of functional multimers, and the response of the lung to microbial challenge and other forms of lung injury.