ORCID ID: 0000-0001-5953-4144 (T.-J.C.).MicroRNA399-mediated regulation of the ubiquitin-conjugating enzyme UBC24/PHOSPHATE2 (PHO2) is crucial for Pi acquisition and translocation in plants. Because of a potential role for PHO2 in protein degradation and its association with membranes, an iTRAQ (for isobaric tags for relative and absolute quantitation)-based quantitative membrane proteomic method was employed to search for components downstream of PHO2. A total of 7491 proteins were identified from Arabidopsis thaliana roots by mass spectrometry, 35.2% of which were predicted to contain at least one transmembrane helix. Among the quantifiable proteins, five were significantly differentially expressed between the wild type and pho2 mutant under two growth conditions. Using immunoblot analysis, we validated the upregulation of several members in PHOSPHATE TRANSPORTER1 (PHT1) family and PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 (PHF1) in pho2 and demonstrated that PHO2 mediates the degradation of PHT1 proteins. Genetic evidence that loss of PHF1 or PHT1;1 alleviated Pi toxicity in pho2 further suggests that they play roles as downstream components of PHO2. Moreover, we showed that PHO2 interacts with PHT1s in the postendoplasmic reticulum compartments and mediates the ubiquitination of endomembrane-localized PHT1;1. This study not only uncovers a mechanism by which PHO2 modulates Pi acquisition by regulating the abundance of PHT1s in the secretory pathway destined for plasma membranes, but also provides a database of the membrane proteome that will be widely applicable in root biology research.
Highlights d First deep proteogenomic landscape of non-smoking lung adenocarcinoma in East Asia d Identified age, sex-related endogenous, and environmental carcinogen mutagenic processes d Proteome-informed classification distinguished clinical features within early stages d Protein networks identified tumorigenesis hallmarks, biomarkers, and druggable targets
STING gain-of-function mutations cause lung disease and T cell cytopenia through unknown mechanisms. Here, we found that these mutants induce chronic activation of ER stress and unfolded protein response (UPR), leading to T cell death by apoptosis in the StingN153S/+ mouse and in human T cells. Mechanistically, STING-N154S disrupts calcium homeostasis in T cells, thus intrinsically primes T cells to become hyperresponsive to T cell receptor signaling–induced ER stress and the UPR, leading to cell death. This intrinsic priming effect is mediated through a novel region of STING that we name “the UPR motif,” which is distinct from known domains required for type I IFN signaling. Pharmacological inhibition of ER stress prevented StingN153S/+ T cell death in vivo. By crossing StingN153S/+ to the OT-1 mouse, we fully restored CD8+ T cells and drastically ameliorated STING-associated lung disease. Together, our data uncover a critical IFN-independent function of STING that regulates calcium homeostasis, ER stress, and T cell survival.
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