The regulation of SMG1 in innate immunity via alternative splicing coupled to nonsense-mediated mRNA decay — ASN Events
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  3. The regulation of SMG1 in innate immunity via alternative splicing coupled to nonsense-mediated mRNA decay

The regulation of SMG1 in innate immunity via alternative splicing coupled to nonsense-mediated mRNA decay (#286)

HUI-CHI LAI 1 2 , James Alexander 1 , De Souza Paul Linus 1 3 , Roberts Tara Laurine 1 2 3
  1. Molecular Oncology Cancer Inflammation, Ingham Institute for Applied Medical Research, Sydney, NSW, Australia
  2. SWS Clinical School, UNSW, Sydney, NSW, Australia
  3. School of Medicine, Western Sydney University, Sydney, NSW, Australia

The protein kinase SMG1 (Suppressor of Morphogenesis in Genitalia 1), is a member of the PIKK (phosphoinositide 3-kinase related kinase) family that includes ATM, ATR and DNA-PK. SMG1 plays a critical role in the mRNA quality control system termed nonsense-mediated decay (NMD). SMG kinase activity is essential for NMD which is a mechanism that protects cells from the accumulation of aberrant mRNAs with premature termination codons (PTCs) which encode for truncated proteins. NMD degrades transcripts with PTCs during the pioneer round of translation and can also be coupled to alternative splicing and this process is referred to as alternative splicing coupled nonsense-mediated decay (AS-NMD). SMG1 knockout mice are embryonic lethal and SMG1 heterozygotes show signs of haploinsufficiency including increased chronic inflammation. To further study the role of SMG1 in inflammation we have generated mice lacking SMG1 in myeloid cells (LysMCreSmg1fl/fl) and control littermates (Smg1fl/fl). Toll-like receptors are components of the innate immune system which detect pathogens and initiate a coordinated immune response. We treated bone marrow derived macrophages (BMM) from Smg1 deficient mice and wild type mice with lipopolysaccharide (an activator of TLR4) and measured genes regulated by alternative splicing (AS) coupled NMD by splicing assays and general NMD targets by real-time PCR. Interestingly, loss of Smg1 may destroy the balance and decrease NMD activity resulting in increased levels of NMD targets. We have also conducted RNA sequencing experiments to further detail how SMG1 loss alters responses to LPS. Preliminary gene ontology analysis shows that, loss of Smg1 alters LPS mediated regulation of the following gene clusters “type I IFN Regulation”, “Defense responses” and “Innate immune responses”; and “Regulation of biochemical processes” (metabolic pathways). Initial laboratory follow up has validated some of these findings. In summary, loss of SMG1 alters NMD activity and creates imbalance in the response to LPS.

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