Department of Public Health and Microbiology, via Santena 9, 10126 Turin, Italy.
J Virol. 2010 May;84(9):4481-93. doi: 10.1128/JVI.02141-09. Epub 2010 Feb 10.
The major immediate-early promoter (MIEP) region of human cytomegalovirus (HCMV) plays a critical role in the regulation of lytic and latent infections by integrating multiple signals supplied by the infecting virus, the type and physiological state of the host cell, and its extracellular surroundings. The interaction of cellular transcription factors with their cognate binding sites, which are present at high densities within the enhancer upstream from the MIEP core promoter, regulate the rate of IE gene transcription and thus affect the outcome of HCMV infection. We have shown previously that the NF-kappaB binding sites within the MIEP enhancer and cellular NF-kappaB activity induced by HCMV infection are required for efficient MIEP activity and viral replication in quiescent cells (P. Caposio, A. Luganini, G. Hahn, S. Landolfo, and G. Gribaudo, Cell. Microbiol. 9:2040-2054, 2007). We now show that the inactivation of either the Elk-1 or serum response factor (SRF) binding site within the enhancer also reduces MIEP activation and viral replication of recombinant HCMV viruses in quiescent fibroblasts. In these cells, we show that the expression of either Elk-1 or SRF is required for optimal IE gene expression, and that the HCMV-stimulated activation of the MEK1/2-ERK1/2 signaling axis leads to Elk-1 transcriptional competency. Furthermore, the replication kinetics of recombinant viruses in which NF-kappaB, Elk-1, and SRF binding sites all are inactivated demonstrate that the higher levels of Elk-1 and SRF binding to MIEP in proliferating cells can compensate even for a lack of HCMV-induced NF-kappaB-mediated MIEP transactivation. These observations highlight the importance of the combination of different MIEP binding sites to optimize IE gene expression in cells in different physiological states.
人类巨细胞病毒（HCMV）的主要早期启动子（MIEP）区域在调节裂解和潜伏感染方面起着关键作用，它整合了感染病毒、宿主细胞的类型和生理状态及其细胞外环境提供的多种信号。细胞转录因子与它们在 MIEP 核心启动子上游增强子中高浓度存在的同源结合位点的相互作用调节 IE 基因转录的速率，从而影响 HCMV 感染的结果。我们之前已经表明，MIEP 增强子中的 NF-κB 结合位点和 HCMV 感染诱导的细胞 NF-κB 活性对于静止细胞中 MIEP 活性和病毒复制的有效进行是必需的（P. Caposio、A. Luganini、G. Hahn、S. Landolfo 和 G. Gribaudo，Cell. Microbiol. 9:2040-2054, 2007）。我们现在表明，增强子中 Elk-1 或血清反应因子（SRF）结合位点的失活也会降低静止成纤维细胞中重组 HCMV 病毒的 MIEP 激活和病毒复制。在这些细胞中，我们表明 Elk-1 或 SRF 的表达对于最佳 IE 基因表达是必需的，并且 HCMV 刺激的 MEK1/2-ERK1/2 信号轴的激活导致 Elk-1 转录能力。此外，在 NF-κB、Elk-1 和 SRF 结合位点均失活的重组病毒的复制动力学表明，在增殖细胞中 Elk-1 和 SRF 结合到 MIEP 的更高水平甚至可以弥补 HCMV 诱导的 NF-κB 介导的 MIEP 反式激活的缺乏。这些观察结果强调了不同 MIEP 结合位点的组合对于优化不同生理状态下细胞中 IE 基因表达的重要性。
