The innate immune kinase TBK1 initiates inflammatory responses to combat infectious pathogens by driving production of type I interferons. TBK1 also controls metabolic processes and promotes oncogene-induced cell proliferation and survival. Here, we demonstrate that TBK1 activates mTOR complex 1 (mTORC1) directly. In cultured cells, TBK1 associates with and activates mTORC1 through site-specific mTOR phosphorylation (on S2159) in response to certain growth factor receptors (i.e., EGF-receptor but not insulin receptor) and pathogen recognition receptors (PRRs) (i.e., TLR3; TLR4), revealing a stimulus-selective role for TBK1 in mTORC1 regulation. By studying cultured macrophages and those isolated from genome edited mTOR S2159A knock-in mice, we show that mTOR S2159 phosphorylation promotes mTORC1 signaling, IRF3 nuclear translocation, and IFN-β production. These data demonstrate a direct mechanistic link between TBK1 and mTORC1 function as well as physiologic significance of the TBK1-mTORC1 axis in control of innate immune function. These data unveil TBK1 as a direct mTORC1 activator and suggest unanticipated roles for mTORC1 downstream of TBK1 in control of innate immunity, tumorigenesis, and disorders linked to chronic inflammation.
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TBK1 (TANK-binding kinase 1) responds to microbial pathogens to initiate cellular responses critical for host innate immune defense. We found previously that TBK1 phosphorylates mTOR (mechanistic target of rapamycin) (on S2159) to increase mTOR complex 1 (mTORC1) activity and signaling in response to the growth factor EGF and the viral dsRNA mimetic poly(I:C). mTORC1 and the less well studied mTORC2 respond to diverse cues to control cellular metabolism, proliferation, and survival. Here we demonstrate that TBK1 activates mTOR complex 2 (mTORC2) directly to increase Akt phosphorylation at physiological levels of protein expression. We find that TBK1 phosphorylates mTOR S2159 within mTORC2 in vitro, phosphorylates mTOR S2159 in cells, and interacts with mTORC2 in cells. By studying MEFs lacking TBK1, as well as MEFs, macrophages, and mice bearing an Mtor S2159A knock-in allele (MtorA/A), we show that TBK1 and mTOR S2159 phosphorylation increase mTORC2 catalytic activity and promote mTOR-dependent downstream signaling to Akt in response to several growth factors and poly(I:C). While microbial-derived stimuli activate TBK1, we find that growth factors fail to activate TBK1 or increase mTOR S2159 phosphorylation in MEFs. Thus, we propose that basal TBK1 activity cooperates with growth factors in parallel to increase mTORC2 (and mTORC1) signaling. Collectively, these results reveal crosstalk between TBK1 and mTOR complexes (mTORCs), key nodes within two major signaling systems. As TBK1 and mTORCs have each been linked to tumorigenesis and metabolic disorders, these kinases may work together in a direct manner in a variety of physiological and pathological settings.
The innate immune kinase TBK1 (TANK-binding kinase 1) responds to microbial-derived signals to initiate responses against viral and bacterial pathogens. More recent work implicates TBK1 in metabolism and tumorigenesis. The kinase mTOR (mechanistic target of rapamycin) integrates diverse environmental cues to control fundamental cellular processes. Our prior work demonstrated in cells that TBK1 phosphorylates mTOR (on S2159) to increase mTORC1 and mTORC2 catalytic activity and signaling. Here we investigate a role for TBK1-mTOR signaling in control of glucose metabolism in vivo. We find that diet induced obese (DIO) but not lean mice bearing a whole-body “TBK1 resistant” Mtor S2159A knockin allele (MtorA/A) display exacerbated hyperglycemia and systemic insulin resistance with no change in energy balance. Mechanistically, Mtor S2159A knockin in DIO mice reduces mTORC1 and mTORC2 signaling in response to insulin and innate immune agonists, reduces anti-inflammatory gene expression in adipose tissue, and blunts anti-inflammatory macrophage M2 polarization, phenotypes shared by mice with tissue-specific inactivation of TBK1 or mTOR complexes. Tissues from DIO mice display elevated TBK1 activity and mTOR S2159 phosphorylation relative to lean mice. We propose a model whereby obesity-associated signals increase TBK1 activity and mTOR phosphorylation, which boosts mTORC1 and mTORC2 signaling in parallel to the insulin pathway, thereby attenuating insulin resistance to improve glycemic control during diet-induced obesity.
<p>The innate immune kinase TBK1 (TANK-binding kinase 1) responds to microbial-derived signals to initiate responses against viral and bacterial pathogens. More recent work implicates TBK1 in metabolism and tumorigenesis. The kinase mTOR (mechanistic target of rapamycin) integrates diverse environmental cues to control fundamental cellular processes. Our prior work demonstrated in cells that TBK1 phosphorylates mTOR (on S2159) to increase mTORC1 and mTORC2 catalytic activity and signaling. Here we investigate a role for TBK1-mTOR signaling in control of glucose metabolism <em>in vivo</em>. We find that diet induced obese (DIO) but not lean mice bearing a whole-body “TBK1 resistant” <em>Mtor</em> S2159A knockin allele (<em>MtorA/A</em>) display exacerbated hyperglycemia and systemic insulin resistance with no change in energy balance. Mechanistically, <em>Mtor</em> S2159A knockin in DIO mice reduces mTORC1 and mTORC2 signaling in response to insulin and innate immune agonists, reduces anti-inflammatory gene expression in adipose tissue, and blunts anti-inflammatory macrophage M2 polarization, phenotypes shared by mice with tissue-specific inactivation of TBK1 or mTOR complexes. Tissues from DIO mice display elevated TBK1 activity and mTOR S2159 phosphorylation relative to lean mice. We propose a model whereby obesity-associated signals increase TBK1 activity and mTOR phosphorylation, which boost mTORC1 and mTORC2 signaling in parallel to the insulin pathway, thereby attenuating insulin resistance to improve glycemic control during diet-induced obesity.</p>
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