Soderling J A, Reed M J, Corsa A, Sage E H
Department of Biological Structure, University of Washington, Seattle 98195-7420, USA.
J Histochem Cytochem. 1997 Jun;45(6):823-35. doi: 10.1177/002215549704500607.
A number of cDNAs (SC1, QR1, and hevin) have been shown to be similar to SPARC (secreted protein acidic and rich in cysteine), a matricellular protein that regulates cell adhesion, cell cycle, and matrix assembly and remodeling. These proteins are 61-65% identical in the final 200 residues of their C-termini; their N-terminal sequences are related but more divergent. All have an overall acidic pl, with a follistatin-like region that is rich in cysteine, and a Ca+2 binding consensus sequence at the C-terminus. Using degenerate primers representing the most highly conserved region in SPARC, SC1, and QR1, we identified a 300-BP SC1 clone in a primary polymerase chain reaction (PCR) screen of a mouse brain cDNA library. This cDNA was used to obtain a full-length clone, which hybridized to a 2.8-KB RNA abundant in brain. Mouse SC1 displays a similarity of 70% to mouse SPARC at the amino acid level. Northern blot and RNAse protection assays revealed a 2.8-KB mRNA expressed at moderate levels (relative to brain) in mouse heart, adrenal gland, epididymis, and lung, and at low levels in kidney, eye, liver, spleen, submandibular gland, and testis. In contrast to SPARC, in situ hybridization showed expression of SC1 mRNA in the tunica media and/or adventitia of medium and large vessels; transcripts were not detected in capillaries, venules, or large lymphatics. The distribution of transcripts for SC1 was also different from that of SPARC in several organs, including adrenal gland, lung, heart, liver, and spleen. Moreover, SC1 mRNA was not evident in endothelium cultured from rat heart, bovine fetal and adult aorta, mouse aorta, human omentum, and bovine retina. Cultured smooth muscle cells and fibroblasts also failed to express SC1 mRNA. The absence of SC1 transcript in cultured cells indicates that the SC1 gene is potentially sensitive to regulatory factors in serum or to a three-dimensional architecture conferred by the extracellular matrix that is lacking in vitro. In conclusion, the expression of SPARC and SC1 appears to be coincident in specific tissues (e.g., adrenal gland and brain), but these proteins exhibit distinct expression patterns in most organs of the mouse. Because SC1 and SPARC are structurally similar and exhibit counteradhesive effects on cultured cells, their overlapping and/or adjacent expression in most tissues predicts that one protein might compensate functionally, at least in part, for the other.
已发现一些cDNA（SC1、QR1和hevin）与SPARC（分泌性富含半胱氨酸的酸性蛋白）相似，SPARC是一种基质细胞蛋白，可调节细胞黏附、细胞周期以及基质组装和重塑。这些蛋白质在其C末端的最后200个残基中具有61%-65%的同一性；它们的N末端序列相关但差异更大。所有这些蛋白质都具有总体酸性的pH值，有一个富含半胱氨酸的卵泡抑素样区域，并且在C末端有一个Ca²⁺结合共有序列。利用代表SPARC、SC1和QR1中最高度保守区域的简并引物，我们在对小鼠脑cDNA文库进行的初次聚合酶链反应（PCR）筛选中鉴定出一个300碱基对的SC1克隆。该cDNA被用于获得一个全长克隆，它与脑中丰富的2.8千碱基RNA杂交。小鼠SC1在氨基酸水平上与小鼠SPARC有70%的相似性。Northern印迹和RNA酶保护分析显示，2.8千碱基的mRNA在小鼠心脏、肾上腺、附睾和肺中以中等水平（相对于脑）表达，而在肾脏、眼睛、肝脏、脾脏、下颌下腺和睾丸中表达水平较低。与SPARC不同，原位杂交显示SC1 mRNA在中、大动脉的中膜和/或外膜中表达；在毛细血管、小静脉或大淋巴管中未检测到转录本。SC1转录本在包括肾上腺、肺、心脏、肝脏和脾脏在内的几个器官中的分布也与SPARC不同。此外，在从大鼠心脏、牛胎儿和成年主动脉、小鼠主动脉、人网膜以及牛视网膜培养的内皮细胞中未发现SC1 mRNA。培养的平滑肌细胞和成纤维细胞也未能表达SC1 mRNA。培养细胞中不存在SC1转录本表明，SC1基因可能对血清中的调节因子或对体外缺乏的细胞外基质赋予的三维结构敏感。总之，SPARC和SC1的表达在特定组织（如肾上腺和脑）中似乎是一致的，但这些蛋白质在小鼠的大多数器官中表现出不同的表达模式。由于SC1和SPARC在结构上相似，并且对培养细胞表现出抗黏附作用，它们在大多数组织中的重叠和/或相邻表达预示着一种蛋白质可能至少部分地在功能上补偿另一种蛋白质。
