Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Virginia, USA; Center for Emerging, Zoonotic, and Arthropod-borne Pathogens, Virginia Polytechnic Institute and State University, Virginia, USA.
National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University, Manassas, VA, USA.
Antiviral Res. 2024 Jun;226:105895. doi: 10.1016/j.antiviral.2024.105895. Epub 2024 Apr 26.
Rift Valley fever virus (RVFV) is an arbovirus in the Phenuiviridae family identified initially by the large 'abortion storms' observed among ruminants; RVFV can also infect humans. In humans, there is a wide variation of clinical symptoms ranging from subclinical to mild febrile illness to hepatitis, retinitis, delayed-onset encephalitis, or even hemorrhagic fever. The RVFV is a tri-segmented negative-sense RNA virus consisting of S, M, and L segments. The L segment encodes the RNA-dependent RNA polymerase (RdRp), termed the L protein, which is responsible for both viral mRNA synthesis and genome replication. Phosphorylation of viral RdRps is known to regulate viral replication. This study shows that RVFV L protein is serine phosphorylated and identified Casein Kinase 1 alpha (CK1α) and protein phosphatase 1 alpha (PP1α) as L protein binding partners. Inhibition of CK1 and PP1 through small molecule inhibitor treatment, D4476 and 1E7-03, respectively, caused a change in the phosphorylated status of the L protein. Inhibition of PP1α resulted in increased L protein phosphorylation whereas inhibition of CK1α decreased L protein phosphorylation. It was also found that in RVFV infected cells, PP1α localized to the cytoplasmic compartment. Treatment of RVFV infected cells with CK1 inhibitors reduced virus production in both mammalian and mosquito cells. Lastly, inhibition of either CK1 or PP1 reduced viral genomic RNA levels. These data indicate that L protein is phosphorylated and that CK1 and PP1 play a crucial role in regulating the L protein phosphorylation cycle, which is critical to viral RNA production and viral replication.
裂谷热病毒（RVFV）是黄病毒科的一种虫媒病毒，最初是通过在反刍动物中观察到的大型“流产风暴”而被发现的；RVFV 也可以感染人类。在人类中，临床症状差异很大，从无症状到轻度发热疾病、肝炎、视网膜炎、迟发性脑炎，甚至出血热。RVFV 是一种三片段负义 RNA 病毒，由 S、M 和 L 片段组成。L 片段编码 RNA 依赖性 RNA 聚合酶（RdRp），称为 L 蛋白，它负责病毒 mRNA 的合成和基因组的复制。病毒 RdRps 的磷酸化被认为可以调节病毒的复制。本研究表明 RVFV L 蛋白是丝氨酸磷酸化的，并鉴定出酪蛋白激酶 1α（CK1α）和蛋白磷酸酶 1α（PP1α）为 L 蛋白结合伴侣。通过小分子抑制剂处理分别抑制 CK1 和 PP1（D4476 和 1E7-03），导致 L 蛋白的磷酸化状态发生变化。抑制 PP1α 导致 L 蛋白磷酸化增加，而抑制 CK1α 导致 L 蛋白磷酸化减少。还发现 PP1α 在 RVFV 感染的细胞中定位于细胞质区室。用 CK1 抑制剂处理 RVFV 感染的细胞可减少哺乳动物和蚊子细胞中的病毒产量。最后，抑制 CK1 或 PP1 均可降低病毒基因组 RNA 水平。这些数据表明 L 蛋白被磷酸化，并且 CK1 和 PP1 在调节 L 蛋白磷酸化循环中发挥关键作用，该循环对病毒 RNA 产生和病毒复制至关重要。
