The pseudophosphatase MK-STYX inhibits stress granule assembly independently of Ser149 phosphorylation of G3BP-1

The pseudophosphatase MK-STYX (mitogen-activated protein kinase phosphoserine/threonine/tyrosine-binding protein) has been implicated in the stress response pathway. The expression of MK-STYX inhibits the assembly of stress granules, which are cytoplasmic storage sites for mRNA that form as a protective mechanism against stressors such as heat shock, UV irradiation and hypoxia. Furthermore, MK-STYX interacts with a key component of stress granules: G3BP-1 (Ras-GTPase activating protein SH3 domain binding protein-1). Because G3BP-1 dephosphorylation at Ser149 induces stress granule assembly, we initially hypothesized that the inhibition of stress granules by MK-STYX was G3BP-1 phosphorylation-dependent. However, in the present study, using MK-STYX constructs and G3BP-1 phosphomimetic or nonphosphorylatable mutants, we show that MK-STYX inhibits stress granule formation independently of G3BP-1 phosphorylation at Ser149. The introduction of point mutations at the active site of MK-STYX that convert serine and phenylalanine to histidine and cysteine, respectively, is sufficient to generate an active enzyme. In separate experiments, we show that this active mutant, MK-STYXactive, has opposite effects to wild-type MK-STYK. Not only does MK-STYXactive induce stress granules, but also it has the capacity to dephosphorylate G3BP-1. Taken together, these results provide evidence that the pseudophosphatase MK-STYX plays a key role in the cellular response to stress

Context-dependent roles of mitochondrial LONP1 in orchestrating the balance between airway progenitor versus progeny cells

While all eukaryotic cells are dependent on mitochondria for function, in a complex tissue, which cell type and which cell behavior are more sensitive to mitochondrial deficiency remain unpredictable. Here, we show that in the mouse airway, compromising mitochondrial function by inactivating mitochondrial protease gene Lonp1 led to reduced progenitor proliferation and differentiation during development, apoptosis of terminally differentiated ciliated cells and their replacement by basal progenitors and goblet cells during homeostasis, and failed airway progenitor migration into damaged alveoli following influenza infection. ATF4 and the integrated stress response (ISR) pathway are elevated and responsible for the airway phenotypes. Such context-dependent sensitivities are predicted by the selective expression of Bok, which is required for ISR activation. Reduced LONP1 expression is found in chronic obstructive pulmonary disease (COPD) airways with squamous metaplasia. These findings illustrate a cellular energy landscape whereby compromised mitochondrial function could favor the emergence of pathological cell types

Injury-induced pulmonary tuft cells are heterogenous, arise independent of key Type 2 cytokines, and are dispensable for dysplastic repair

While the lung bears significant regenerative capacity, severe viral pneumonia can chronically impair lung function by triggering dysplastic remodeling. The connection between these enduring changes and chronic disease remains poorly understood. We recently described the emergence of tuft cells within Krt5+ dysplastic regions after influenza injury. Using bulk and single-cell transcriptomics, we characterized and delineated multiple distinct tuft cell populations that arise following influenza clearance. Distinct from intestinal tuft cells which rely on Type 2 immune signals for their expansion, neither IL-25 nor IL-4ra signaling are required to drive tuft cell development in dysplastic/injured lungs. In addition, tuft cell expansion occurred independently of type I or type III interferon signaling. Furthermore, tuft cells were also observed upon bleomycin injury, suggesting that their development may be a general response to severe lung injury. While intestinal tuft cells promote growth and differentiation of surrounding epithelial cells, in the lungs of tuft cell deficient mice, Krt5+ dysplasia still occurs, goblet cell production is unchanged, and there remains no appreciable contribution of Krt5+ cells into more regionally appropriate alveolar Type 2 cells. Together, these findings highlight unexpected differences in signals necessary for murine lung tuft cell amplification and establish a framework for future elucidation of tuft cell functions in pulmonary health and disease

Single-cell multiomic profiling of human lungs reveals cell-type-specific and age-dynamic control of SARS-CoV2 host genes.

Respiratory failure associated with COVID-19 has placed focus on the lungs. Here, we present single-nucleus accessible chromatin profiles of 90,980 nuclei and matched single-nucleus transcriptomes of 46,500 nuclei in non-diseased lungs from donors of ~30 weeks gestation,~3 years and ~30 years. We mapped candidate cis-regulatory elements (cCREs) and linked them to putative target genes. We identified distal cCREs with age-increased activity linked to SARS-CoV-2 host entry gene TMPRSS2 in alveolar type 2 cells, which had immune regulatory signatures and harbored variants associated with respiratory traits. At the 3p21.31 COVID-19 risk locus, a candidate variant overlapped a distal cCRE linked to SLC6A20, a gene expressed in alveolar cells and with known functional association with the SARS-CoV-2 receptor ACE2. Our findings provide insight into regulatory logic underlying genes implicated in COVID-19 in individual lung cell types across age. More broadly, these datasets will facilitate interpretation of risk loci for lung diseases