Takito J, Yan L, Ma J, Hikita C, Vijayakumar S, Warburton D, Al-Awqati Q
Departments of Medicine and Physiology, College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA.
Am J Physiol. 1999 Aug;277(2):F277-89. doi: 10.1152/ajprenal.1999.277.2.F277.
The band 3 anion exchanger is located in the apical membrane of a beta-intercalated clonal cell line, whereas the vacuolar H(+)-ATPase is present in the basolateral membrane. When these cells were seeded at confluent density, they converted to an alpha-phenotype, localizing each of these proteins to the opposite cell membrane domain. The reversal of polarity is induced by hensin, a 230-kDa extracellular matrix protein. Rabbit kidney hensin is a multidomain protein composed of eight SRCR ("scavenger receptor, cysteine rich"), two CUB ("C1r/C1s Uegf Bmp1"), and one ZP ("zona pellucida") domain. Other proteins known to have these domains include CRP-ductin, a cDNA expressed at high levels in mouse intestine (8 SRCR, 5 CUB, 1 ZP), ebnerin, a protein cloned from a rat taste bud library (4 SRCR, 3 CUB, 1 ZP), and DMBT1, a sequence in human chromosome 10q25-26 frequently deleted in malignant gliomas (9 SRCR, 2 CUB, 1 ZP). Rabbit and mouse hensin genomic clones contained a new SRCR that was not found in hensin cDNA but was homologous to the first SRCR domain in DMBT1. Furthermore, the 3'-untranslated regions and the signal peptide of hensin were homologous to those of DMBT1. Mouse genomic hensin was localized to chromosome 7 band F4, which is syntenic to human 10q25-26. These data suggest that hensin and DMBT1 are alternatively spliced forms of the same gene. The analysis of mouse hensin bacterial artificial chromosome (BAC) genomic clone by sequencing and Southern hybridization revealed that the gene also likely encodes CRP-ductin. A new antibody against the mouse SRCR1 domain recognized a protein in the mouse and rabbit brain but not in the immortalized cell line or kidney, whereas an antibody to SRCR6 and SRCR7 domains which are present in all the transcripts, recognized proteins in intestine, kidney, and brain from several species. The most likely interpretation of these data is that one gene produces at least three transcripts, namely, hensin, DMBT1, and CRP-ductin. Hensin may participate in determining the polarized phenotype of other epithelia and brain cells.
带3阴离子交换蛋白位于β-闰细胞克隆系的顶端膜，而液泡型H⁺-ATP酶存在于基底外侧膜。当这些细胞以汇合密度接种时，它们转变为α表型，使这些蛋白质中的每一种都定位到相对的细胞膜结构域。极性反转是由hensin诱导的，hensin是一种230 kDa的细胞外基质蛋白。兔肾hensin是一种多结构域蛋白，由八个富含半胱氨酸的清道夫受体（SRCR）结构域、两个C1r/C1s、Uegf、Bmp1（CUB）结构域和一个透明带（ZP）结构域组成。已知具有这些结构域的其他蛋白质包括CRP-ductin，一种在小鼠肠道中高水平表达的cDNA（8个SRCR、5个CUB、1个ZP）；ebnerin，一种从大鼠味蕾文库中克隆的蛋白质（4个SRCR、3个CUB、1个ZP）；以及DMBT1，人类染色体10q25 - 26上的一个序列，在恶性胶质瘤中经常缺失（9个SRCR、2个CUB、1个ZP）。兔和小鼠的hensin基因组克隆包含一个新的SRCR，该结构域在hensin cDNA中未发现，但与DMBT1中的第一个SRCR结构域同源。此外，hensin的3'非翻译区和信号肽与DMBT1的同源。小鼠基因组hensin定位于7号染色体F4带，与人类10q25 - 26同线。这些数据表明hensin和DMBT1是同一基因的可变剪接形式。通过测序和Southern杂交对小鼠hensin细菌人工染色体（BAC）基因组克隆进行分析表明，该基因也可能编码CRP-ductin。一种针对小鼠SRCR1结构域的新抗体识别小鼠和兔脑中的一种蛋白质，但在永生化细胞系或肾脏中未识别到，而针对所有转录本中都存在的SRCR6和SRCR7结构域的抗体，识别几种物种的肠道、肾脏和脑中的蛋白质。这些数据最可能的解释是一个基因产生至少三种转录本，即hensin、DMBT1和CRP-ductin。Hensin可能参与决定其他上皮细胞和脑细胞的极化表型。
