Department of Microbiology and Immunology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA.
Department of Microbiology and Immunology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA
J Virol. 2020 Apr 16;94(9). doi: 10.1128/JVI.02177-19.
Lipoxin A4 (LXA4) is an endogenous lipid mediator with compelling anti-inflammatory and proresolution properties. Studies done to assess the role of arachidonic acid pathways of the host in Kaposi's sarcoma-associated herpesvirus (KSHV) biology helped discover that KSHV infection hijacks the proinflammatory cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LO) pathways and concurrently reduces anti-inflammatory LXA4 secretion to maintain KSHV latency in infected cells. Treatment of KSHV-infected cells with LXA4 minimizes the activation of inflammatory and proliferative signaling pathways, including the NF-κB, AKT, and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways, but the exact mechanism of action of LXA4 remains unexplored. Here, using mass spectrometry analysis, we identified components from the minichromosome maintenance (MCM) protein and chromatin-remodeling complex SMARCB1 and SMARCC2 to be LXA4-interacting host proteins in KSHV-infected cells. We identified a higher level of nuclear aryl hydrocarbon receptor (AhR) in LXA4-treated KSHV-infected cells than in untreated KSHV-infected cells, which probably facilitates the affinity interaction of the nucleosome complex protein with LXA4. We demonstrate that SMARCB1 regulates both replication and transcription activator (RTA) activity and host hedgehog (hh) signaling in LXA4-treated KSHV-infected cells. Host hedgehog signaling was modulated in an AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR)-S6 kinase-dependent manner in LXA4-treated KSHV-infected cells. Since anti-inflammatory drugs are beneficial as adjuvants to conventional and immune-based therapies, we evaluated the potential of LXA4 treatment in regulating programmed death-ligand 1 (PD-L1) on KSHV-carrying tumor cells. Overall, our study identified LXA4-interacting host factors in KSHV-infected cells, which could help provide an understanding of the mode of action of LXA4 and its therapeutic potential against KSHV. The latent-to-lytic switch in KSHV infection is one of the critical events regulated by the major replication and transcription activator KSHV protein called RTA. Chromatin modification of the viral genome determines the phase of the viral life cycle in the host. Here, we report that LXA4 interacts with a host chromatin modulator, especially SMARCB1, which upregulates the KSHV ORF50 promoter. SMARCB1 has also been recognized to be a tumor suppressor protein which controls many tumorigenic events associated with the hedgehog (hh) signaling pathway. We also observed that LXA4 treatment reduces PD-L1 expression and that PD-L1 expression is an important immune evasion strategy used by KSHV for its survival and maintenance in the host. Our study underscores the role of LXA4 in KSHV biology and emphasizes that KSHV is strategic in downregulating LXA4 secretion in the host to establish latency. This study also uncovers the therapeutic potential of LXA4 and its targetable receptor, AhR, in KSHV's pathogenesis.
脂氧素 A4（LXA4）是一种内源性脂质介质，具有强大的抗炎和促解决特性。为评估宿主花生四烯酸途径在卡波西肉瘤相关疱疹病毒（KSHV）生物学中的作用而进行的研究发现，KSHV 感染劫持了促炎环氧化酶-2（COX-2）和 5-脂氧合酶（5-LO）途径，同时减少抗炎 LXA4 的分泌，以维持感染细胞中的 KSHV 潜伏期。用 LXA4 处理 KSHV 感染的细胞，可最大限度地减少炎症和增殖信号通路的激活，包括 NF-κB、AKT 和细胞外信号调节激酶 1/2（ERK1/2）通路，但 LXA4 的确切作用机制仍未得到探索。在这里，我们使用质谱分析，鉴定了来自微小染色体维持（MCM）蛋白和染色质重塑复合物 SMARCB1 和 SMARCC2 的成分，这些都是 KSHV 感染细胞中与 LXA4 相互作用的宿主蛋白。我们发现，用 LXA4 处理 KSHV 感染的细胞后，核芳香烃受体（AhR）的水平高于未用 LXA4 处理的 KSHV 感染的细胞，这可能有助于核小体复合物蛋白与 LXA4 的亲和相互作用。我们证明，SMARCB1 调节 LXA4 处理的 KSHV 感染细胞中的复制和转录激活剂（RTA）活性和宿主 hedgehog（hh）信号。在 LXA4 处理的 KSHV 感染的细胞中，宿主 hedgehog 信号通过 AMP 激活的蛋白激酶（AMPK）-雷帕霉素靶蛋白（mTOR）-S6 激酶依赖的方式进行调节。由于抗炎药物作为传统和免疫为基础的治疗方法的辅助剂是有益的，我们评估了 LXA4 治疗在调节 KSHV 携带肿瘤细胞上程序性死亡配体 1（PD-L1）中的潜在作用。总的来说，我们在 KSHV 感染的细胞中鉴定了与 LXA4 相互作用的宿主因子，这有助于我们了解 LXA4 的作用模式及其对 KSHV 的治疗潜力。KSHV 感染的潜伏到裂解的转换是由主要的复制和转录激活剂 KSHV 蛋白 RTA 调节的关键事件之一。病毒基因组的染色质修饰决定了宿主中病毒生命周期的阶段。在这里，我们报告 LXA4 与宿主染色质调节剂，特别是 SMARCB1，相互作用，上调 KSHV ORF50 启动子。SMARCB1 也被认为是一种肿瘤抑制蛋白，它控制着与 hedgehog（hh）信号通路相关的许多肿瘤发生事件。我们还观察到 LXA4 处理可降低 PD-L1 的表达，而 PD-L1 的表达是 KSHV 用于在宿主中存活和维持的重要免疫逃逸策略。我们的研究强调了 LXA4 在 KSHV 生物学中的作用，并强调 KSHV 策略性地下调宿主中 LXA4 的分泌以建立潜伏期。这项研究还揭示了 LXA4 及其可靶向受体 AhR 在 KSHV 发病机制中的治疗潜力。
