Biology subjects

Sempeck, C.

Publications and source records attributed to Sempeck, C..

3 recordsLinked to original sources

bioRxiv2024

Cyanobacteria form a procarboxysome-like structure in response to high CO2

Fixing 25% of CO2 globally, cyanobacteria are integral to climate change efforts. The cyanobacterial CO2 concentrating mechanism (CCM) features the carboxysome, a bacterial microcompartment which houses their CO2 fixing machinery. The proteinaceous shell of the carboxysome restricts diffusion of CO2, both inward and outward. While necessary for CCM function in air (0.04% CO2), when grown in high CO2 levels (3% CO2) representative of early earth, the shell would harmfully limit CO2 fixation. To understand how carboxysomes change form and function in response to increased CO2 conditions, we used a Grx1-roGFP2 redox sensor and single cell timelapse fluorescence microscopy to track subcellular redox states of Synechococcus sp. PCC 7002 grown in air or 3% CO2. Comparing different levels of compartmentalization, we targeted the cytosol, a shell-less carboxysomal assembly intermediate called the procarboxysome, and the carboxysome. The carboxysome redox state was dynamic and, under 3% CO2, procarboxysome-like structures formed and mirrored cytosolic redox states, indicating that a more permeable shell architecture may be favorable when [CO2] is high. This work represents a step in understanding how cyanobacteria respond to changing CO2 concentrations and the selective forces driving carboxysome evolution.

biochemistry↗

bioRxiv2022

The APE2 nuclease is essential for DNA double strand break repairby microhomology-mediated end-joining.

Microhomology-mediated end-joining (MMEJ) is an intrinsically mutagenic pathway of DNA double strand break repair essential for proliferation of homologous recombination (HR) deficient tumors. While targeting MMEJ has emerged as a powerful strategy to eliminate HR-deficient (HRD) cancers, this is limited by an incomplete understanding of the mechanism and factors required for MMEJ repair. Here, we identify the APE2 nuclease as a novel MMEJ effector. We show that loss of APE2 blocks the fusion of deprotected telomeres by MMEJ and inhibits MMEJ in DNA repair reporter assays to levels comparable to Pol Theta suppression. Mechanistically, we demonstrate that APE2 possesses intrinsic flap-cleaving activity, that its MMEJ function in cells depends on its nuclease domain and further identify uncharacterized domains required for recruitment to damaged DNA. We conclude that HR-deficient cells are addicted to APE2 due to a previously unappreciated role in MMEJ, which could be exploited in the treatment of cancer.

molecular biology↗

bioRxiv2020

JAK1 inhibition blocks lethal sterile immune responses:implications for COVID-19 therapy

Cytokine storms are drivers of pathology and mortality in myriad viral infections affecting the human population. In SARS-CoV-2-infected patients, the strength of the cytokine storm has been associated with increased risk of acute respiratory distress syndrome, myocardial damage, and death. However, the therapeutic value of attenuating the cytokine storm in COVID-19 remains to be defined. Here, we report results obtained using a novel mouse model of lethal sterile anti-viral immune responses. Using a mouse model of Down syndrome (DS) with a segmental duplication of a genomic region encoding four of the six interferon receptor genes (Ifnrs), we demonstrate that these animals overexpress Ifnrs and are hypersensitive to IFN stimulation. When challenged with viral mimetics that activate Toll-like receptor signaling and IFN anti-viral responses, these animals overproduce key cytokines, show exacerbated liver pathology, rapidly lose weight, and die. Importantly, the lethal immune hypersensitivity, accompanying cytokine storm, and liver hyperinflammation are blocked by treatment with a JAK1-specific inhibitor. Therefore, these results point to JAK1 inhibition as a potential strategy for attenuating the cytokine storm and consequent organ failure during overdrive immune responses. Additionally, these results indicate that people with DS, who carry an extra copy of the IFNR gene cluster encoded on chromosome 21, should be considered at high risk during the COVID-19 pandemic. One Sentence SummaryInhibition of the JAK1 kinase prevents pathology and mortality caused by a rampant innate immune response in mice.

immunology↗