During viral infection, sensing of cytosolic DNA by the cyclic GMP-AMP synthase (cGAS) activates the adaptor protein STING and triggers an antiviral response. Little is known about the mechanisms that determine the kinetics of activation and deactivation of the cGAS-STING pathway, ensuring effective but controlled innate antiviral responses. Here we found that the ubiquitin ligase Trim38 targets cGas for sumoylation in uninfected cells and during the early phase of viral infection. Sumoylation of cGas prevented its polyubiquitination and degradation. Trim38 also sumoylated Sting during the early phase of viral infection, promoting both Sting activation and protein stability. In the late phase of infection, cGas and Sting were desumoylated by Senp2 and subsequently degraded via proteasomal and chaperone-mediated autophagy pathways, respectively. Our findings reveal an essential role for Trim38 in the innate immune response to DNA virus and provide insight into the mechanisms that ensure optimal activation and deactivation of the cGAS-STING pathway.

Traditionally, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a 91 kDa transcription factor, regulates lipid metabolism and long-chain fatty acid oxidation by upregulating the expression of several genes of the tricarboxylic acid cycle and the mitochondrial fatty acid oxidation pathway. In addition, PGC-1α regulates the expression of mitochondrial genes to control mitochondria DNA replication and cellular oxidative metabolism. Recently, new insights showed that several myokines such as irisin and myostatin are epigenetically regulated by PGC-1α in skeletal muscles, thereby modulating systemic energy balance, with marked expansion of mitochondrial volume density and oxidative capacity in healthy or diseased myocardia. In addition, in our studies evaluating whether PGC-1α overexpression in epicardial adipose tissue can act as a paracrine organ to improve or repair cardiac function, we found that overexpression of hepatic PGC-1α increased hepatic fatty acid oxidation and decreased triacylglycerol storage and secretion in vivo and in vitro. In this review, we discuss recent studies showing that PGC-1α may regulate mitochondrial fusion–fission homeostasis and affect the renal function in acute or chronic kidney injury. Furthermore, PGC-1α is an emerging protein with a biphasic role in cancer, acting both as a tumor suppressor and a tumor promoter and thus representing a new and unresolved topic for cancer biology studies. In summary, this review paper demonstrates that PGC-1α plays a central role in coordinating the gene expression of key components of mitochondrial biogenesis and as a critical metabolic regulator in many vital organs, including white and brown adipose tissue, skeletal muscle, heart, liver, and kidney.

High insulin/IGF is a biologic link between diabetes and cancers, but the underlying molecular mechanism remains unclear. Here we report a previously unrecognized tumour-promoting mechanism for stress protein TRB3, which mediates a reciprocal antagonism between autophagic and proteasomal degradation systems and connects insulin/IGF to malignant promotion. We find that several human cancers express higher TRB3 and phosphorylated insulin receptor substrate 1, which correlates negatively with patient's prognosis. TRB3 depletion protects against tumour-promoting actions of insulin/IGF and attenuates tumour initiation, growth and metastasis in mice. TRB3 interacts with autophagic receptor p62 and hinders p62 binding to LC3 and ubiquitinated substrates, which causes p62 deposition and suppresses autophagic/proteasomal degradation. Several tumour-promoting factors accumulate in cancer cells to support tumour metabolism, proliferation, invasion and metastasis. Interrupting TRB3/p62 interaction produces potent antitumour efficacies against tumour growth and metastasis. Our study opens possibility of targeting this interaction as a potential novel strategy against cancers with diabetes.

Viral DNA sensing within the cytosol of infected cells activates type I interferon (IFN) expression. MITA/STING plays an essential role in this pathway by acting as both a sensor for the second messenger cGAMP and as an adaptor for downstream signaling components. In an expression screen for proteins that can activate the IFNB1 promoter, we identified the ER-associated protein ZDHHC1 as a positive regulator of virus-triggered, MITA/STING-dependent immune signaling. Zdhhc1(-/-) cells failed to effectively produce IFNs and other cytokines in response to infection with DNA but not RNA viruses. Zdhhc1(-/-) mice infected with the neurotropic DNA virus HSV-1 exhibited lower cytokine levels and higher virus titers in the brain, resulting in higher lethality. ZDHHC1 constitutively associated with MITA/STING and mediates dimerization/aggregation of MITA/STING and recruitment of the downstream signaling components TBK1 and IRF3. These findings support a role for ZDHHC1 in mediating MITA/STING-dependent innate immune response against DNA viruses.

MicroRNA-494 mediates apoptosis and necrosis in several types of cells, but its renal target and potential role in AKI are unknown. Here, we found that microRNA-494 binds to the 39UTR of activating transcription factor 3 (ATF3) and decreases its transcription. In mice, overexpression of microRNA-494 significantly attenuated the level of ATF3 and induced inflammatory mediators, such as IL-6, monocyte chemotactic protein-1, and P-selectin, after renal ischemia/reperfusion, exacerbating apoptosis and further decreasing renal function. Activation of NF-kB mediated this proinflammatory response. In this ischemia/reperfusion model, urinary levels of microRNA-494 increased significantly before the rise in serum creatinine. In humans, urinary microRNA-494 levels were 60-fold higher in patients with AKI than normal controls. In conclusion, upregulation of microRNA-494 contributes to inflammatory or adhesion molecule-induced kidney injury after ischemia/reperfusion by inhibiting expression of ATF3. Furthermore, microRNA-494 may be a specific and noninvasive biomarker for AKI.