Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Proc Natl Acad Sci U S A. 2022 Jun 21;119(25):e2206046119. doi: 10.1073/pnas.2206046119. Epub 2022 Jun 15.
Nuclear speckles are non-membrane-bound organelles known as storage sites for messenger RNA (mRNA) processing and splicing factors. More recently, nuclear speckles have also been implicated in splicing and export of a subset of mRNAs, including the influenza virus M mRNA that encodes proteins required for viral entry, trafficking, and budding. However, little is known about how nuclear speckles are assembled or regulated. Here, we uncovered a role for the cellular protein kinase TAO2 as a constituent of nuclear speckles and as a factor required for the integrity of these nuclear bodies and for their functions in pre-mRNA splicing and trafficking. We found that a nuclear pool of TAO2 is localized at nuclear speckles and interacts with nuclear speckle factors involved in RNA splicing and nuclear export, including SRSF1 and Aly/Ref. Depletion of TAO2 or inhibition of its kinase activity disrupts nuclear speckle structure, decreasing the levels of several proteins involved in nuclear speckle assembly and splicing, including SC35 and SON. Consequently, splicing and nuclear export of influenza virus M mRNA were severely compromised and caused a disruption in the virus life cycle. In fact, low levels of TAO2 led to a decrease in viral protein levels and inhibited viral replication. Additionally, depletion or inhibition of TAO2 resulted in abnormal expression of a subset of mRNAs with key roles in viral replication and immunity. Together, these findings uncovered a function of TAO2 in nuclear speckle formation and function and revealed host requirements and vulnerabilities for influenza infection.
核斑点是非膜结合细胞器，已知是信使 RNA（mRNA）加工和剪接因子的储存位点。最近，核斑点也被牵连到亚组 mRNA 的剪接和输出中，包括编码病毒进入、运输和出芽所需蛋白的流感病毒 M mRNA。然而，关于核斑点如何组装或调节，知之甚少。在这里，我们揭示了细胞蛋白激酶 TAO2 作为核斑点的组成部分的作用，以及作为这些核体完整性及其在 pre-mRNA 剪接和运输中的功能所必需的因素的作用。我们发现 TAO2 的核池定位于核斑点，并与涉及 RNA 剪接和核输出的核斑点因子相互作用，包括 SRSF1 和 Aly/Ref。TAO2 的耗竭或其激酶活性的抑制破坏了核斑点结构，降低了参与核斑点组装和剪接的几种蛋白质的水平，包括 SC35 和 SON。结果，流感病毒 M mRNA 的剪接和核输出受到严重损害，并导致病毒生命周期中断。事实上，TAO2 水平低会导致病毒蛋白水平降低并抑制病毒复制。此外，TAO2 的耗竭或抑制导致与病毒复制和免疫有关的关键作用的亚组 mRNA 的异常表达。总之，这些发现揭示了 TAO2 在核斑点形成和功能中的作用，并揭示了宿主对流感感染的需求和脆弱性。
