The mechanistic target of rapamycin (mTOR) has a key role in the integration of various physiological stimuli to regulate several cell growth and metabolic pathways1. mTOR primarily functions as a catalytic subunit in two structurally related but functionally distinct multi-component kinase complexes, mTOR complex 1 (mTORCl) and mTORC2 (refs 1, 2). Dysregulation of mTOR signalling is associated with a variety of human diseases, including metabolic disorders and cancer1. Thus, both mTORCl and mTORC2 kinase activity is tightly controlled in cells. mTORCl is activated by both nutrients3–6 and growth factors7, whereas mTORC2 responds primarily to extracellular cues such as growth-factor-triggered activation of PI3K signalling8–10. Although both mTOR and GβL (also known as MLST8) assemble into mTORC1 and mTORC2 (refs 11–15), it remains largely unclear what drives the dynamic assembly of these two functionally distinct complexes. Here we show, in humans and mice, that the K63-linked polyubiquitination status of GβL dictates the homeostasis of mTORC2 formation and activation. Mechanistically, the TRAF2 E3 ubiquitin ligase promotes K63-linked polyubiquitination of GβL, which disrupts its interaction with the unique mTORC2 component SIN1 (refs 12–14) to favour mTORC1 formation. By contrast, the OTUD7B deubiquitinase removes polyubiquitin chains from GβL to promote GβL interaction with SIN1, facilitating mTORC2 formation in response to various growth signals. Moreover, loss of critical ubiquitination residues in GβL, by either K305R/K313R mutations or a melanoma-associated GβL(ΔW297) truncation, leads to elevated mTORC2 formation, which facilitates tumorigenesis, in part by activating AKT oncogenic signalling. In support of a physiologically pivotal role for OTUD7B in the activation of mTORC2/AKT signalling, genetic deletion of Otud7b in mice suppresses Akt activation and Kras-driven lung tumorigenesis in vivo. Collectively, our study reveals a GβL-ubiquitination-dependent switch that fine-tunes the dynamic organization and activation of the mTORC2 kinase under both physiological and pathological conditions.

The kinase TBK1 responds to microbial stimuli and mediates type I interferon (IFN-I) induction. We show that TBK1 is also a central mediator of growth factor signaling; this function relies on a specific adaptor, TBK-binding protein 1 (TBKBP1). TBKBP1 recruits TBK1 to PKCθ via a scaffold protein, Card10, which allows PKCθ to phosphorylate TBK1 at serine-716, a crucial step for TBK1 activation by growth factors but not by innate immune stimuli. While the TBK1/ TBKBP1 signaling axis is dispensable for IFN-I induction, it mediates mTORC1 activation and oncogenesis. Lung epithelial cell-conditional deletion of either TBK1 or TBKBP1 inhibits tumorigenesis in a mouse model of lung cancer. In addition to promoting tumor growth, the TBK1/TBKBP1 axis facilitates tumor-mediated immunosuppression by a mechanism involving induction of the checkpoint molecule PD-L1 and stimulation of glycolysis. These findings suggest a PKCθ-TBKBP1-TBK1 growth factor signaling axis mediating both tumor growth and immunosuppression.

Molecules containing damage-associated molecular patterns (DAMP) play an important role in many pathogenic processes. Our aim was to investigate the role of IL-33, a DAMP molecule, in adenovirus (Ad)-induced liver inflammation. Ad-infected mice exhibited a steadily increased IL-33 and its receptor ST2 expression in the liver during the first week of the infection. Treatment of exogenous IL-33 resulted in a great decrease in the serum alanine aminotransferase (ALT) levels and the number of Councilman bodies in the liver. Attenuated liver injury by IL-33 correlated with an increase in T regulatory (Treg) cells but with a decrease in macrophages, dendritic cells and NK cells in the liver. IL-33 enhanced both type 1 (IL-2 and IFN-γ) and type 2 (IL-5 and IL-13) immune responses in infected mice. However, IL-33 inhibited TNF-α expression in hepatic T cells and macrophages, and significantly reduced TNF-α levels in the liver. We found that in addition to its direct effects, IL-33 strongly induced novel nuocytes in the livers and spleens of infected mice. When co-cultured with nuocytes, hepatic T cells and macrophages expressed lower levels of TNF-α. The IL-33-treated mice also demonstrated a slight delay, but no significant impairment, in eliminating an intrahepatic infection with Ad. In conclusion, this study reveals that IL-33 acts as a potent immune stimulator and a hepatoprotective cytokine in acute viral hepatitis. Its direct immunoregulatory functions and ability to induce novel nuocytes further suggest to us that it may be a potentially promising therapeutic candidate for the management of viral hepatitis.

Xiao et al. demonstrate that a protein kinase, TBK1, regulates the function of dendritic cells in mediating immune responses.

NF-κB inducing kinase (NIK) is a central component of the noncanonical NF-κB signaling pathway. Although NIK has been extensively studied for its function in the regulation of lymphoid organ development and B-cell maturation, the role of NIK in regulating T cell functions remains unclear and controversial. Using T cell-conditional NIK knockout mice, we here demonstrate that although NIK is dispensable for thymocyte development, it has a cell-intrinsic role in regulating the homeostasis and function of peripheral T cells. T cell-specific NIK ablation reduced the frequency of effector/memory-like T cells and impaired T cell responses to bacterial infection. The T cell-conditional NIK knockout mice were also defective in generation of inflammatory T cells and refractory to the induction of a T cell-dependent autoimmune disease, experimental autoimmune encephalomyelitis. Our data suggest a crucial role for NIK in mediating the generation of effector T cells and their recall responses to antigens. Together, these findings establish NIK as a cell-intrinsic mediator of T cell functions in both immune and autoimmune responses.