Browsing by Author "Akula, Murali K"
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Item Open Access Control of the innate immune response by the mevalonate pathway.(Nat Immunol, 2016-08) Akula, Murali K; Shi, Man; Jiang, Zhaozhao; Foster, Celia E; Miao, David; Li, Annie S; Zhang, Xiaoman; Gavin, Ruth M; Forde, Sorcha D; Germain, Gail; Carpenter, Susan; Rosadini, Charles V; Gritsman, Kira; Chae, Jae Jin; Hampton, Randolph; Silverman, Neal; Gravallese, Ellen M; Kagan, Jonathan C; Fitzgerald, Katherine A; Kastner, Daniel L; Golenbock, Douglas T; Bergo, Martin O; Wang, DonghaiDeficiency in mevalonate kinase (MVK) causes systemic inflammation. However, the molecular mechanisms linking the mevalonate pathway to inflammation remain obscure. Geranylgeranyl pyrophosphate, a non-sterol intermediate of the mevalonate pathway, is the substrate for protein geranylgeranylation, a protein post-translational modification that is catalyzed by protein geranylgeranyl transferase I (GGTase I). Pyrin is an innate immune sensor that forms an active inflammasome in response to bacterial toxins. Mutations in MEFV (encoding human PYRIN) result in autoinflammatory familial Mediterranean fever syndrome. We found that protein geranylgeranylation enabled Toll-like receptor (TLR)-induced activation of phosphatidylinositol-3-OH kinase (PI(3)K) by promoting the interaction between the small GTPase Kras and the PI(3)K catalytic subunit p110δ. Macrophages that were deficient in GGTase I or p110δ exhibited constitutive release of interleukin 1β that was dependent on MEFV but independent of the NLRP3, AIM2 and NLRC4 inflammasomes. In the absence of protein geranylgeranylation, compromised PI(3)K activity allows an unchecked TLR-induced inflammatory responses and constitutive activation of the Pyrin inflammasome.Item Open Access Protein prenylation restrains innate immunity by inhibiting Rac1 effector interactions.(Nature communications, 2019-09-04) Akula, Murali K; Ibrahim, Mohamed X; Ivarsson, Emil G; Khan, Omar M; Kumar, Israiel T; Erlandsson, Malin; Karlsson, Christin; Xu, Xiufeng; Brisslert, Mikael; Brakebusch, Cord; Wang, Donghai; Bokarewa, Maria; Sayin, Volkan I; Bergo, Martin ORho family proteins are prenylated by geranylgeranyltransferase type I (GGTase-I), which normally target proteins to membranes for GTP-loading. However, conditional deletion of GGTase-I in mouse macrophages increases GTP-loading of Rho proteins, leading to enhanced inflammatory responses and severe rheumatoid arthritis. Here we show that heterozygous deletion of the Rho family gene Rac1, but not Rhoa and Cdc42, reverses inflammation and arthritis in GGTase-I-deficient mice. Non-prenylated Rac1 has a high affinity for the adaptor protein Ras GTPase-activating-like protein 1 (Iqgap1), which facilitates both GTP exchange and ubiquitination-mediated degradation of Rac1. Consistently, inactivating Iqgap1 normalizes Rac1 GTP-loading, and reduces inflammation and arthritis in GGTase-I-deficient mice, as well as prevents statins from increasing Rac1 GTP-loading and cytokine production in macrophages. We conclude that blocking prenylation stimulates Rac1 effector interactions and unleashes proinflammatory signaling. Our results thus suggest that prenylation normally restrains innate immune responses by preventing Rac1 effector interactions.