Lin C S, Chang C H, Huynh T
Department of Stomatology, University of California, San Francisco 94143-0512, USA.
DNA Cell Biol. 1997 Jan;16(1):9-16. doi: 10.1089/dna.1997.16.9.
Plastins (or fimbrins) are a family of actin-binding proteins that are conserved from yeast to humans. In mammals, three tissue-specific plastin isoforms have been identified. The L isoform (L-plastin) is normally expressed only in leukocytes but is also found in >90% of neoplastic nonleukocyte human cells. Because L-plastin expression in tissue-specifically regulated in both humans and rodents, it is likely that similar mechanisms regulate L-plastin gene expression in human and rodent cells and that they could be identified by comparing the function and nucleotide sequences of the human and murine L-plastin gene promoters. Previously, we reported the isolation and characterization of the human L-plastin gene promoter. In this study, we isolated a murine L-plastin 5' end cDNA and used it as a probe to isolate several murine genomic clones. A representative clone contained 7 kb of the flanking region, 0.1 kb of the first exon, and 9.9 kb of the first intron. A continuous 1,354-bp sequence was identified around the first exon. Five transcription initiation sites were found 40 to 73 bp downstream from a perfect TATA box. Alignment of the sequence with its human counterpart revealed approximately 60% homology in a 1-kb region spanning the first exon and the flanking region. The TATA box, one ER binding site, and two ETS binding sites were completely conserved. An Sp1 binding sequence in the human promoter was partially conserved in the murine promoter but could still bind to Sp1. A second ER binding sequence, lying 5' adjacent to the TATA box in the human promoter, was conserved only at the 3' half-site in the murine promoter; the 5' half-site was changed into a potential AP1 binding site. This AP1/ER hybrid sequence was incapable of binding to ER. However, both human and murine promoters were found to function equally well in either human or murine leukocytes.
丝束蛋白（或丝束肌动蛋白结合蛋白）是一类从酵母到人类都保守的肌动蛋白结合蛋白家族。在哺乳动物中，已鉴定出三种组织特异性丝束蛋白异构体。L异构体（L-丝束蛋白）通常仅在白细胞中表达，但在超过90%的人类肿瘤非白细胞细胞中也有发现。由于L-丝束蛋白的表达在人类和啮齿动物中都是组织特异性调节的，因此很可能类似的机制调节人类和啮齿动物细胞中L-丝束蛋白基因的表达，并且可以通过比较人类和小鼠L-丝束蛋白基因启动子的功能和核苷酸序列来鉴定它们。此前，我们报道了人类L-丝束蛋白基因启动子的分离和表征。在本研究中，我们分离了一个小鼠L-丝束蛋白5'端cDNA，并将其用作探针来分离几个小鼠基因组克隆。一个代表性克隆包含7 kb的侧翼区域、0.1 kb的第一个外显子和9.9 kb的第一个内含子。在第一个外显子周围鉴定出一个连续的1354 bp序列。在一个完美的TATA框下游40至73 bp处发现了五个转录起始位点。该序列与其人类对应序列的比对显示，在跨越第一个外显子和侧翼区域的1 kb区域中，同源性约为60%。TATA框、一个雌激素受体（ER）结合位点和两个E26转录因子（ETS）结合位点完全保守。人类启动子中的一个Sp1结合序列在小鼠启动子中部分保守，但仍能与Sp1结合。人类启动子中位于TATA框5'相邻位置的第二个ER结合序列，在小鼠启动子中仅在3'半位点保守；5'半位点变成了一个潜在的活化蛋白1（AP1）结合位点。这个AP1/ER杂合序列不能与ER结合。然而，发现人类和小鼠启动子在人类或小鼠白细胞中功能同样良好。
