MISTR: A conserved MItochondrial STress Response network revealed by signatures of evolutionary conflict

Host-pathogen conflicts leave genetic signatures of variation in homologous host genes. Using these “molecular scars” as a guide, we discovered a vertebrate-specific MItochondrial STress Response circuit (MISTR). MISTR proteins are associated with electron transport chain factors and activated by stress signals such as interferon-gamma and hypoxia. Upon stress, ultraconserved miRNAs downregulate MISTR1 followed by replacement with paralogs MISTR AntiViral (MISTRAV) or MISTR Hypoxia (MISTRH), depending on the insult. While cells lacking MISTR1 are more sensitive to apoptotic triggers, cells lacking MISTRAV or expressing the poxvirus-encoded vMISTRAV exhibit resistance to the same insults. Rapid evolution signatures across primate genomes for MISTR1 and MISTRAV indicate ancient and ongoing conflicts with pathogens. MISTR proteins are also found in plants, yeasts, and an algal virus indicating ancient origins and suggesting diverse means of altering mitochondrial function under stress. The discovery of MISTR circuitry highlights the use of evolution-guided studies to reveal fundamental biological processes.


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Innate immunity is a critical frontline host defense mechanism in response to pathogen infection.

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At the onset of infections in vertebrates, a set of more than 400 genes are transcriptionally upregulated 51 by interferon and thus termed interferon-stimulated genes (ISGs). ISGs display diverse functions such 52 as activation of cell death programs and recruitment of immune cells (e.g. dendritic cells (Schneider et       To investigate MISTRAV biology, we generated three A549 clonal cell lines -C15∆1, C15∆2, C15∆3 -182 with distinct indels that disrupted the MISTRAV ORF using CRISPR/CAS ( Figure 3A). A549 cells were 183 selected because: 1) MISTRAV is interferon-inducible in these cells ( Figure 1D, Figure

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Based on MISTRAV mitochondrial localization and numerous documented connections between 198 immune responses involving cell death mediated through mitochondria, we reasoned that MISTR might 199 mediate apoptotic responses. We primed WT and KO cells with IFN-g then added the commonly used 200 activator of apoptosis, staurosporine (STS), for 16 hours followed by functional analysis ( Figure 3E).

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Assays were normalized to either untreated controls or to the number of cells being tested to account for 202 differences in proliferation rates (Figure 3-figure supplement 1). Interestingly, we observed that C15∆1 203 and C15∆2 displayed reduced sensitivity to STS, while C15∆3 showed increased sensitivity to STS 204 compared to WT cells ( Figure 3F). Consistent with these results, we detected robust caspase-3/7 205 cleavage activity for C15∆3 compared to WT ( Figure 3G; p<0.0001). In addition, detectable decreases in 206 caspase-3/7 activity were observed for C15∆1 and C15∆2 relative to WT treated cells ( Figure 3G; 207 p<0.0001). The differential sensitivities of the clones to STS relative to WT were consistent with levels of 9 PARP cleavage across the clones in response to STS ( Figure 3H). These data suggest a role for 209 MISTRAV and miR-147b in apoptosis.

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We define MISTRAV as an IFN-g-inducible gene ( Figure 1D) and protein ( Figure   proposed circuit had not been tested ( Figure 5H).

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Our model predicts that MISTR1 is a ubiquitously expressed sensor of stress. Specific stress 369 signals induce miRNA expression leading to the downregulation of MISTR1 and its replacement by

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The embedded nature of miR-147b implies a step-wise molecular progression of this response.

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The next day, cells were transfected with 50 ng/well of the psiCHECK-2 (Promega) construct using the

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HeLa cells were fixed and stained with mitoTracker Red (Thermo). Images were taken in the confocal 533 microscopy core at the University of Utah.

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The location of pre-mir-147b is marked by the blue box below predicted protein-coding mRNAs.