LncRNA MIAT regulates autophagy and apoptosis of macrophage infected by Mycobacterium tuberculosis through the miR-665/ULK1 signaling axis.

Accumulating lines of evidence have revealed the involvement of long non-coding RNAs (lncRNAs) in the control and elimination of invading Mycobacterium tuberculosis (Mtb) by macrophage. In this study, we sought to elucidate the role of MIAT on autophagy and apoptosis of Mtb-infected macrophage and to reveal the molecular mechanism. We observed that the expression of MIAT was heightened while miR-665 level was declined in THP-1 cells with Bacillus Calmette-Guerin (BCG) infection in a time-dependent manner. Functionally, disruption of MIAT effectively facilitated cell viability and restricted apoptosis ability concomitant with the downregulation of Bax and cleaved caspase-3 along with an accumulation of Bcl-2 in BCG-infected THP-1 cells. Concurrently, the interference of MIAT dramatically disinhibited macrophage autophagy as characterized by diminution of autophagy related markers LC3-II and Beclin-1 as well as increment of p62 in THP-1 cells following BCG infection. Concordantly, depletion of MIAT was found to noticeably aggrandize Mtb survival. Importantly, MIAT served as a ceRNA for sponging miR-665 and negatively regulated its expression. ULK1 was identified as an authentic target of miR-665 and modulated by MIAT. Mechanistically, the functional role of MIAT depletion in macrophage apoptosis and autophagy were tremendously abrogated by the depression of miR-665 and enrichment of ULK1. Overall, the preceding observations clearly illuminated that MIAT was elevated in human macrophage response to BCG infection, and functioned as a negative regulator in autophagy and antimicrobial effects by manipulating miR-665/ULK1 axis during Mtb infection, which may provide a promising target for developing an anti-bacterial against TB.

Mechanistic target of rapamycin-mediated autophagy is involved in the alleviation of lipopolysaccharide-induced acute lung injury in rats.

Acute lung injury (ALI) is a complex clinical syndrome with high morbidity and mortality rates. Autophagy is an adaptive process that plays a complex role in ALI. The aim of this study was to investigate the effects of autophagy on lipopolysaccharide (LPS)-induced lung injury by establishing a rat ALI model and to further explore the possible mechanisms involved. Rats were pretreated with the autophagy inhibitor 3-methyladenine (3-MA) or the autophagy activator rapamycin before they were challenged with the intratracheal instillation of LPS (5 mg/kg). The level of autophagy in the lung tissue was detected. Lung injury and vascular permeability were assessed. The role of the mechanistic target of rapamycin (mTOR)-mediated Unc-51-like kinase 1 (ULK1) and the class III PI3 kinase VPS34 in autophagy regulation was examined. LPS challenge induced autophagy and rapamycin pretreatment enhanced autophagy activity in LPS-induced ALI rats. LPS caused severe lung injury and high pulmonary vascular permeability, which could be alleviated by enhancing autophagy. In addition, the inhibition of mTOR upregulated the expression of ULK1 and VPS34 and thus increased LPS-induced autophagy. Autophagy plays a protective role in LPS-induced ALI, and enhancing autophagy via the inhibition of mTOR alleviates lung injury and pulmonary barrier function. Moreover, mTOR negatively mediates ULK1 and VPS34 to regulate LPS-induced autophagy in rats.

TBK-binding protein 1 regulates IL-15-induced autophagy and NKT cell survival.

The cytokine IL-15 mediates development and survival of immune cells, including natural killer T (NKT) cells, but the underlying mechanism of IL-15 function is incompletely understood. Here we show that IL-15 induces autophagy in NKT cells with a mechanism that involves a crucial signaling component, TBK-binding protein 1 (Tbkbp1). Tbkbp1 facilitates activation of the autophagy-initiating kinase Ulk1 through antagonizing the inhibitory action of mTORC1. This antagonization involves the recruitment of an mTORC1-opposing phosphatase to Ulk1. Tbkbp1 deficiency attenuates IL-15-stimulated NKT cell autophagy, and is associated with mitochondrial dysfunction, aberrant ROS production, defective Bcl2 expression and reduced NKT cell survival. Consequently, Tbkbp1-deficient mice have profound deficiency in NKT cells, especially IFN-γ-producing NKT1. We further show that Tbkbp1 regulates IL-15-stimulated autophagy and survival of NK cells. These findings suggest a mechanism of autophagy induction by IL-15, and establish Tbkbp1 as a regulator of NKT cell development and survival.

Pro-inflammation Associated with a Gain-of-Function Mutation (R284S) in the Innate Immune Sensor STING.

The cellular sensor stimulator of interferon genes (STING) initiates type I interferon (IFN) and cytokine production following association with cyclic dinucleotides (CDNs) generated from intracellular bacteria or via a cellular synthase, cGAS, after binding microbial or self-DNA. Although essential for protecting the host against infection, unscheduled STING signaling is now known to be responsible for a variety of autoinflammatory disorders. Here, we report a gain-of-function mutation in STING (R284S), isolated from a patient who did not require CDNs to augment activity and who manifested a constitutively active phenotype. Control of the Unc-51-like autophagy activating kinase 1 (ULK1) pathway, which has previously been shown to influence STING function, was potently able to suppress STING (R284S) activity to alleviate cytokine production. Our findings add to the growing list of inflammatory syndromes associated with spontaneous STING signaling and provide a therapeutic strategy for the treatment of STING-induced inflammatory disease.

Beyond autophagy: New roles for ULK1 in immune signaling and interferon responses.

The human serine/threonine kinase ULK1 is the human homolog of the Caenorhabditis elegans Unc-51 kinase and of the Saccharomyces cerevisiae autophagy-related protein kinase Atg1. As Unc-51 and Atg1, ULK1 regulates both axon growth and autophagy, respectively, in mammalian cells. However, a novel immunoregulatory role of ULK1 has been recently described. This kinase was shown to be required for regulation of both type I interferon (IFN) production and induction of type I IFN signaling. Optimal regulation of IFN production is crucial for generation of effective IFN-immune responses, and defects in such networks can be detrimental for the host leading to uncontrolled pathogen infection, tumor growth, or autoimmune diseases. Thus, ULK1 plays a central role in IFN-dependent immunity. Here we review the diverse roles of ULK1, with special focus on its importance to type I IFN signaling, and highlight important future study questions.