Browsing by Author "Digman, Michelle A."

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    Differential integrated stress response and asparagine production drive symbiosis and therapy resistance of pancreatic adenocarcinoma cells
    (Springer Nature, 2022) Halbrook, Christopher J.; Thurston, Galloway; Boyer, Seth; Anaraki, Cecily; Jiménez, Jennifer A.; McCarthy, Amy; Steele, Nina G.; Kerk, Samuel A.; Hong, Hanna S.; Lin, Lin; Law, Fiona V.; Felton, Catherine; Scipioni, Lorenzo; Sajjakulnukit, Peter; Andren, Anthony; Beutel, Alica K.; Singh, Rima; Nelson, Barbara S.; Van Den Bergh, Fran; Krall, Abigail S.; Mullen, Peter J.; Zhang, Li; Batra, Sandeep; Morton, Jennifer P.; Stanger, Ben Z.; Christofk, Heather R.; Digman, Michelle A.; Beard, Daniel A.; Viale, Andrea; Zhang, Ji; Crawford, Howard C.; di Magliano, Marina Pasca; Jorgensen, Claus; Lyssiotis, Costas A.; Pediatrics, School of Medicine
    The pancreatic tumor microenvironment drives deregulated nutrient availability. Accordingly, pancreatic cancer cells require metabolic adaptations to survive and proliferate. Pancreatic cancer subtypes have been characterized by transcriptional and functional differences, with subtypes reported to exist within the same tumor. However, it remains unclear if this diversity extends to metabolic programming. Here, using metabolomic profiling and functional interrogation of metabolic dependencies, we identify two distinct metabolic subclasses among neoplastic populations within individual human and mouse tumors. Furthermore, these populations are poised for metabolic cross-talk, and in examining this, we find an unexpected role for asparagine supporting proliferation during limited respiration. Constitutive GCN2 activation permits ATF4 signaling in one subtype, driving excess asparagine production. Asparagine release provides resistance during impaired respiration, enabling symbiosis. Functionally, availability of exogenous asparagine during limited respiration indirectly supports maintenance of aspartate pools, a rate-limiting biosynthetic precursor. Conversely, depletion of extracellular asparagine with PEG–asparaginase sensitizes tumors to mitochondrial targeting with phenformin.
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    A Loop Region in the N-Terminal Domain of Ebola Virus VP40 Is Important in Viral Assembly, Budding, and Egress
    (Multidisciplinary Digital Publishing Institute (MDPI), 2014-10-17) Adu-Gyamfi, Emmanuel; Soni, Smita P.; Jee, Clara S.; Digman, Michelle A.; Gratton, Enrico; Stahelin, Robert V.; Department of Biochemistry & Molecular Biology, IU School of Medicine-South Bend
    Ebola virus (EBOV) causes viral hemorrhagic fever in humans and can have clinical fatality rates of ~60%. The EBOV genome consists of negative sense RNA that encodes seven proteins including viral protein 40 (VP40). VP40 is the major Ebola virus matrix protein and regulates assembly and egress of infectious Ebola virus particles. It is well established that VP40 assembles on the inner leaflet of the plasma membrane of human cells to regulate viral budding where VP40 can produce virus like particles (VLPs) without other Ebola virus proteins present. The mechanistic details, however, of VP40 lipid-interactions and protein-protein interactions that are important for viral release remain to be elucidated. Here, we mutated a loop region in the N-terminal domain of VP40 (Lys127, Thr129, and Asn130) and find that mutations (K127A, T129A, and N130A) in this loop region reduce plasma membrane localization of VP40. Additionally, using total internal reflection fluorescence microscopy and number and brightness analysis we demonstrate these mutations greatly reduce VP40 oligomerization. Lastly, VLP assays demonstrate these mutations significantly reduce VLP release from cells. Taken together, these studies identify an important loop region in VP40 that may be essential to viral egress.