Wolf F W, Marks R M, Sarma V, Byers M G, Katz R W, Shows T B, Dixit V M
Department of Pathology, University of Michigan Medical Center, Ann Arbor 48109.
J Biol Chem. 1992 Jan 15;267(2):1317-26.
The response of endothelial cells to the cytokine tumor necrosis factor-alpha (TNF) is complex, involving the induction and suppression of multiple genes and gene products. Differential screening of a TNF-stimulated, cycloheximide-treated human umbilical vein endothelial cell library has resulted in the cloning of several novel cDNAs whose protein products are involved in the primary response of the endothelium to TNF. One of these cDNAs, designated B12, is further characterized here. B12 is encoded by a 3.5-kilobase transcript and is induced rapidly and transiently by TNF. Transcript expression is found to be developmentally regulated in a tissue-specific manner, with B12 message being differentially expressed in the heart and liver during mouse embryogenesis. The open reading frame of B12 predicts a 316-amino acid sequence rich in charged residues, particularly at the carboxyl terminus, and has neither significant homology to other known proteins nor to any extent sequence motifs. B12 is found to be a highly conserved single-copy gene which is located in the q22----q23 region of human chromosome 17. Polyclonal antibodies raised against a large portion of the B12 open reading frame immunoprecipitate a 36-kilodalton polypeptide from wheat germ lysates programmed to translate in vitro transcribed B12 mRNA. The B12 protein is further shown to be induced in human umbilical vein endothelial cells by TNF, and the protein is shown to be rapidly degraded.
内皮细胞对细胞因子肿瘤坏死因子-α（TNF）的反应是复杂的，涉及多个基因和基因产物的诱导与抑制。对经TNF刺激并用放线菌酮处理的人脐静脉内皮细胞文库进行差异筛选，已克隆出几个新的cDNA，其蛋白质产物参与内皮细胞对TNF的初级反应。其中一个名为B12的cDNA在此进一步进行了特性分析。B12由一个3.5千碱基的转录本编码，可被TNF迅速且短暂地诱导。发现转录本表达在发育过程中以组织特异性方式受到调控，在小鼠胚胎发育期间，B12信息在心脏和肝脏中差异表达。B12的开放阅读框预测出一个富含带电荷残基的316个氨基酸序列，特别是在羧基末端，并且与其他已知蛋白质既无显著同源性，也没有任何程度的序列基序。发现B12是一个高度保守的单拷贝基因，位于人类染色体17的q22----q23区域。针对B12开放阅读框的大部分区域产生的多克隆抗体，从小麦胚芽裂解物中免疫沉淀出一个36千道尔顿的多肽，该裂解物经编程用于体外翻译转录的B12 mRNA。进一步表明，B12蛋白在人脐静脉内皮细胞中可被TNF诱导，且该蛋白会迅速降解。
