Nguyen H, Lin R, Hiscott J
Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Department of Microbiology, McGill University, Montreal, Quebec, Canada.
Oncogene. 1997 Sep 18;15(12):1425-35. doi: 10.1038/sj.onc.1201318.
Interferon Regulatory Factor (IRF)-1 has been characterized as an important growth regulatory and immunomodulatory transcription factor. To further characterize the potential targets of IRF-1 antiproliferative activity, IRF-1 was expressed under the control of the tetracycline-inducible system in murine NIH3T3 cells. Due to their ability to mimic IRF-1 transactivator function, the regulatory potential of IRF-1/RelA and IRF-2/RelA fusion proteins consisting of the DNA binding domains of IRF-1 or IRF-2 fused to the transactivation domain of NF-kappaB RelA(p65) was also examined. Cells inducibly expressing IRF-1 or IRF/RelA in response to doxycycline treatment displayed significantly reduced growth rates compared to control cells, and inhibition of cell growth correlated directly with the level of transgene expression. Interestingly, IRF-1 and IRF/RelA expression also induced a low level of apoptosis, as detected by microscopic analyses. Furthermore, expression of the interferon inducible, double stranded RNA dependent kinase PKR was increased following IRF-1 or IRF/RelA induction. Most strikingly, induction of IRF-1 and IRF/RelA expression resulted in a significant increase in STAT1 (p91) protein and increased ISGF3 DNA binding activity, suggesting that IRF-1 tumor suppressor activity may involve a novel mechanism which activates the JAK-STAT pathway through STAT1. WAF1 levels were also constitutively elevated in IRF-1 and IRF-1/RelA cells. These studies demonstrate that inducible expression of the transactivation function of IRF-1 or IRF/RelA mediates tumor suppressor activity by inducing cell growth arrest, apoptosis and the differential activation of growth regulatory genes such as PKR, STAT1 and WAF1.
干扰素调节因子（IRF）-1已被确定为一种重要的生长调节和免疫调节转录因子。为了进一步明确IRF-1抗增殖活性的潜在靶点，在四环素诱导系统的控制下，在小鼠NIH3T3细胞中表达了IRF-1。由于它们能够模拟IRF-1反式激活因子的功能，因此还检测了由IRF-1或IRF-2的DNA结合结构域与NF-κB RelA（p65）的反式激活结构域融合而成的IRF-1/RelA和IRF-2/RelA融合蛋白的调节潜力。与对照细胞相比，在强力霉素处理下可诱导表达IRF-1或IRF/RelA的细胞显示出显著降低的生长速率，并且细胞生长的抑制与转基因表达水平直接相关。有趣的是，通过显微镜分析检测发现，IRF-1和IRF/RelA的表达也诱导了低水平的细胞凋亡。此外，在IRF-1或IRF/RelA诱导后，干扰素诱导的双链RNA依赖性激酶PKR的表达增加。最引人注目的是，IRF-1和IRF/RelA表达的诱导导致STAT1（p91）蛋白显著增加以及ISGF3 DNA结合活性增强，这表明IRF-1的肿瘤抑制活性可能涉及一种通过STAT1激活JAK-STAT途径的新机制。在IRF-1和IRF-1/RelA细胞中，WAF1水平也持续升高。这些研究表明，IRF-1或IRF/RelA反式激活功能的诱导表达通过诱导细胞生长停滞、细胞凋亡以及生长调节基因如PKR、STAT1和WAF1的差异激活来介导肿瘤抑制活性。
