Project Description The MacDuff lab studies inflammatory and innate immune responses to pathogenic and commensal microbes. We are interested in understanding how the immune system controls inflammatory responses to different microbes, particularly in the gastro-intestinal tract that is home to billions of commensal bacteria. We are currently focusing on a protein complex called the Linear Ubiquitin Chain Assembly Complex (LUBAC), which plays a central role in regulating many immune signaling pathways and inflammation. Humans with LUBAC deficiency have a lethal disease characterized by immunodeficiency, autoinflammation, and myopathy and cardiomyopathy. LUBAC is composed of three proteins: HOIL1, HOIP and Sharpin, and is the only known enzyme capable of generating linear (also known as methionine-1-linked) ubiquitin chains.
Using HOIL1-deficient mice and cells, we recently found that HOIL1 is important for cells to make interferons in response to murine norovirus infection, and to control norovirus replication in vivo. These results were surprising, because several publications had indicated that LUBAC inhibits the production of interferons after infection with viruses such as Sendai virus and vesicular stomatitis virus. Interferons are critical mediators of the immune response to viral infections and can be induced in virus-infected cells through the activation of several different cytoplasmic RNA sensors. These include the RIG-I-like receptors, RIG-I and MDA5. RIG-I and MDA5 can sense different viral families, but signal through a common pathway on the mitochondrial membrane that leads to the transcriptional activation of interferon and establishes an anti-viral environment. We found that HOIL1 is essential for cells to make interferon after infection with viruses that are sensed by MDA5, but not with viruses that are sensed by RIG-I, such as Sendai virus and vesicular stomatitis virus. These results are still perplexing because RIG-I and MDA5 are thought to activate the same signaling pathway leading to expression of interferon. Future experiments will be aimed at identifying the mechanism by which HOIL1 and LUBAC differentially regulate RIG-I- and MDA5-dependent interferon induction.
Potential rotation projects include:
1) Identify protein domains of HOIL1 (and HOIP, Sharpin) that are important for interferon production during viral infection.
2) Identify new HOIL1 interacting proteins (in the MDA5 signaling pathway).
3) Identify proteins that are ubiquitinated by HOIL1 (we have recently found that HOIL1 E3 ubiquitin ligase activity is required).
4) Test whether HOIL1 alters post-translational modifications on MDA5 (i.e.phosphorylation, ubiquitination etc)
5) Test whether HOIL1 expression in macrophages, dendritic cells or intestinal epithelial cells is important to control viral replication in vivo. Additional projects currently on-going in the lab include defining the role of LUBAC in regulating inflammatory responses to commensal and pathogenic bacteria in the gastro-intestinal tract.
1) MacDuff DA, Baldridge MT, Qaqish AM, Nice TJ, Darbandi AD, Hartley VL, Peterson ST, Miner JJ, Iwai K, Virgin HW. HOIL1 is essential for the induction of type I and III interferons by MDA5 and regulates persistent murine norovirus infection. J Virol. 2018 Sept 12. JVI.01368-18.
2) MacDuff DA, Reese TA, Kimmey JM, Weiss LA, Song C, Zhang X, Kambal A, Duan E, Carrero JA, Boisson B, Laplantine E, Israël A, Picard C, Colonna C, Edelson BT, Sibley LD, Stallings CL, Casanova JL, Iwai K, and Virgin HW. Phenotypic complementation of genetic immunodeficiency by chronic herpesvirus infection. eLife 2015;4:e04494.
MacDuff Lab Presentation
MacDuff Lab JVI 2018