PKR Transduces MDA5-Dependent Signals for Type I IFN Induction.

Sensing invading pathogens early in infection is critical for establishing host defense. Two cytosolic RIG-like RNA helicases, RIG-I and MDA5, are key to type I interferon (IFN) induction in response to viral infection. Mounting evidence suggests that another viral RNA sensor, protein kinase R (PKR), may also be critical for IFN induction during infection, although its exact contribution and mechanism of action are not completely understood. Using PKR-deficient cells, we found that PKR was required for type I IFN induction in response to infection by vaccinia virus lacking the PKR antagonist E3L (VVΔE3L), but not by Sendai virus or influenza A virus lacking the IFN-antagonist NS1 (FluΔNS1). IFN induction required the catalytic activity of PKR, but not the phosphorylation of its principal substrate, eIF2α, or the resulting inhibition of host translation. In the absence of PKR, IRF3 nuclear translocation was impaired in response to MDA5 activators, VVΔE3L and encephalomyocarditis virus, but not during infection with a RIG-I-activating virus. Interestingly, PKR interacted with both RIG-I and MDA5; however, PKR was only required for MDA5-mediated, but not RIG-I-mediated, IFN production. Using an artificially activated form of PKR, we showed that PKR activity alone was sufficient for IFN induction. This effect required MAVS and correlated with IRF3 activation, but no longer required MDA5. Nonetheless, PKR activation during viral infection was enhanced by MDA5, as virus-stimulated catalytic activity was impaired in MDA5-null cells. Taken together, our data describe a critical and non-redundant role for PKR following MDA5, but not RIG-I, activation to mediate MAVS-dependent induction of type I IFN through a kinase-dependent mechanism.

Rationale and design of the Prone Position and Respiratory Outcomes in Non-intubated COVID-19 PatiEnts: The "PRONE" Study.

While benefits of prone position in mechanically-ventilated patients have been well-described, a randomized-control trial to determine the effects of prone positioning in awake, spontaneously-breathing patients with an acute pneumonia has not been previously conducted. Prone Position and Respiratory Outcomes in Non-Intubated COVID-19 PatiEnts: the "PRONE" Study (PRONE) was conducted in non-intubated hospitalized patients with coronavirus disease 2019 (COVID-19) pneumonia as defined by respiratory rate ≥ 20/min or an oxyhemoglobin saturation (SpO2) ≤ 93% without supplemental oxygen [1]. The PRONE trial was designed to investigate the effects of prone positioning on need for escalation in respiratory support, as defined by need for transition to a higher acuity level of care, increased fraction of inspired oxygen (FiO2), or the initiation of invasive mechanical ventilation. Secondary objectives were to assess the duration of effect of prone positioning on respiratory parameters such as respiratory rate and SpO2, as well as other outcomes such as time to discharge or transition in level of care.

Inhibition of nonsense-mediated RNA decay by the tumor microenvironment promotes tumorigenesis.

While nonsense-mediated RNA decay (NMD) is an established mechanism to rapidly degrade select transcripts, the physiological regulation and biological significance of NMD are not well characterized. We previously demonstrated that NMD is inhibited in hypoxic cells. Here we show that the phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) translation initiation factor by a variety of cellular stresses leads to the inhibition of NMD and that eIF2α phosphorylation and NMD inhibition occur in tumors. To explore the significance of this NMD regulation, we used an unbiased approach to identify approximately 750 NMD-targeted mRNAs and found that these mRNAs are overrepresented in stress response and tumor-promoting pathways. Consistent with these findings, the inhibition of NMD promotes cellular resistance to endoplasmic reticulum stress and encourages tumor formation. The transcriptional and translational regulations of gene expression by the microenvironment are established mechanisms by which tumor cells adapt to stress. These data indicate that NMD inhibition by the tumor microenvironment is also an important mechanism to dynamically regulate genes critical for the response to cellular stress and tumorigenesis.