All animals must maintain genome and proteome integrity, especially when experiencing endogenous or exogenous stress. To cope, organisms have evolved sophisticated and conserved response systems: unfolded protein responses (UPRs) ensure proteostasis while the DNA damage response (DDR) maintains genome integrity. Emerging evidence suggests that UPRs and DDRs crosstalk, but the extent of crosstalk remains poorly understood. Here, we demonstrate that inactivation of the DNA primasespri-1andpri-2, which synthesize RNA primers at replication forks and whose inactivation causes DNA damage, activates the UPR of the endoplasmic reticulum (UPR-ER) inCaenorhabditis elegans, with especially strong activation in the germline. We observed activation of both the inositol-requiring-enzyme 1 (ire-1) and the protein kinase RNA-like ER kinase (PEK-1) branches of the UPR-ER. Interestingly, activation of the UPR-ER output genehsp-4/BiPwas partially independent of its canonical activators,ire-1andxbp-1, and instead required the third branch of the UPR-ER,atf-6, suggesting functional redundancy. We further found that primase depletion specifically induces the UPR-ER, but not the mechanistically distinct cytosolic or mitochondrial UPRs, suggesting that primase inactivation causes compartment-specific rather than global stress. Functionally, loss ofire-1orpek-1sensitized animals to replication stress caused by hydroxyurea. Finally, transcriptome analysis ofpri-1embryos revealed several deregulated processes that could cause UPR-ER activation, including protein glycosylation, calcium signaling, and fatty acid desaturation. Together, our data show that the UPR-ER, but not other UPRs, responds to replication fork stress and that the UPR-ER is required to alleviate this stress.
Campylobacter jejuniis a leading cause of bacterial gastroenteritis worldwide. Acute infection can be antecedent to highly debilitating long-term sequelae. Expression of iron acquisition systems is vital forC. jejunito survive the low iron availability within the human gut. TheC. jejuni fetMP-fetABCDEFgene cluster is known to be upregulated during human infection and under iron limitation. While FetM and FetP have been functionally linked to iron transport in prior work, here we assess the contribution by each of the downstream genes (fetABCDEF) toC. jejunigrowth during both iron-depleted and iron-replete conditions. Significant growth impairment was observed upon disruption offetA, fetB, fetCandfetD, suggesting a role in iron acquisition for each encoded protein. FetA expression was modulated by iron-availability but not dependent on the presence of FetB, FetC, FetD, FetE or FetF. Functions of the putative thioredoxins FetE and FetF were redundant in iron scavenging, requiring a double deletion (ΔfetEF) to exhibit a growth defect.C. jejuniFetE was expressed and the structure solved to 1.50 Å, revealing structural similarity to thiol-disulfide oxidases. Functional characterization in biochemical assays showed that FetE reduced insulin at a slower rate thanE. coliTrx and that together, FetEF promoted substrate oxidation in cell extracts, suggesting that FetE (and presumably FetF) are oxidoreductases that can mediate oxidationin vivo. This study advances our understanding of the contributions by thefetMP-fetABCDEFgene cluster to virulence at a genetic and functional level, providing foundational knowledge towards mitigatingC. jejuni-related morbidity and mortality.
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