Perkins D, Wang Z, Donovan C, He H, Mark D, Guan G, Wang Y, Walunas T, Bluestone J, Listman J, Finn P W
Renal Division, Brigham and Women's Hospitals, Boston, MA 02115, USA.
J Immunol. 1996 Jun 1;156(11):4154-9.
T cell activation requires at least two distinct signals, including signaling via the Ag-specific TCR and a costimulatory pathway. The best characterized costimulatory pathway involves the CD28 molecule, which is expressed constitutively on T cells and binds the family of B7 counter-receptors on APCs. Inhibition of this costimulatory pathway prevents T cell activation and can lead to long-term T cell unresponsiveness or anergy. In contrast, CTLA4, which is homologous to CD28, has been shown to be a negative regulator of T cell activation. The CTLA4 molecule is not expressed on resting T cells, but is induced after the initial steps of T cell activation. To address the regulation of CTLA4 expression, we have analyzed CTLA4 at the level of cell surface expression, mRNA, rate of transcription, and rate of decay of message. Nuclear runoff results show an increase in the rate of transcription following T cell activation. Our analyses of non-T cells, including B cells, mastocytoma, and fibroblasts, by Northern blot analysis detect only T cell expression of CTLA4. Reporter gene analysis indicates that 335 bp of upstream CTLA4 sequence are sufficient to control inducibility. We have identified important regulatory regions that control inducible and cell-specific CTLA4 expression. These results also suggest that both positive and negative response elements modulate the transcriptional regulation of CTLA4 gene expression. Understanding the regulation of CTLA4 should provide insight into the regulation of T cell activation at the molecular level.
T细胞活化至少需要两个不同的信号，包括通过抗原特异性TCR的信号传导和共刺激途径。最具特征的共刺激途径涉及CD28分子，其在T细胞上组成性表达，并与APC上的B7反受体家族结合。抑制该共刺激途径可防止T细胞活化，并可导致长期的T细胞无反应性或无能。相比之下，与CD28同源的CTLA4已被证明是T细胞活化的负调节因子。CTLA4分子在静息T细胞上不表达，但在T细胞活化的初始步骤后被诱导。为了研究CTLA4表达的调控，我们在细胞表面表达、mRNA、转录速率和信息衰减速率水平上分析了CTLA4。核转录分析结果显示T细胞活化后转录速率增加。我们通过Northern印迹分析对包括B细胞、肥大细胞瘤和成纤维细胞在内的非T细胞进行分析，仅检测到CTLA4的T细胞表达。报告基因分析表明，CTLA4上游序列的335 bp足以控制诱导性。我们已经鉴定出控制诱导性和细胞特异性CTLA4表达的重要调控区域。这些结果还表明，正负反应元件均调节CTLA4基因表达的转录调控。了解CTLA4的调控应该能在分子水平上深入了解T细胞活化的调控。
