Zhixue Liu

AMPK regulates autophagy by phosphorylating BECN1 at threonine 388

ABSTRACT Macroautophagy/autophagy is a conserved catabolic process that recycles cytoplasmic material during low energy conditions. BECN1/Beclin1 (Beclin 1, autophagy related) is an essential protein for function of the class 3 phosphatidylinositol 3-kinase (PtdIns3K) complexes that play a key role in autophagy nucleation and elongation. Here, we show that AMP-activated protein kinase (AMPK) regulates autophagy by phosphorylating BECN1 at Thr388. Phosphorylation of BECN1 is required for autophagy upon glucose withdrawal. BECN1T388A, a phosphorylation defective mutant, suppresses autophagy through decreasing the interaction between PIK3C3 (phosphatidylinositol 3-kinase catalytic subunit type 3) and ATG14 (autophagy-related 14). The BECN1T388A mutant has a higher affinity for BCL2 than its wild-type counterpart; the mutant is more prone to dimer formation. Conversely, a BECN1 phosphorylation mimic mutant, T388D, has stronger binding to PIK3C3 and ATG14, and promotes higher autophagy activity than the wild-type control. These findings uncover a novel mechanism of autophagy regulation.

PAQR3 controls autophagy by integrating AMPK signaling to enhance ATG14L‐associated PI3K activity

The Beclin1–VPS34 complex is recognized as a central node in regulating autophagy via interacting with diverse molecules such as ATG14L for autophagy initiation and UVRAG for autophagosome maturation. However, the underlying molecular mechanism that coordinates the timely activation of VPS34 complex is poorly understood. Here, we identify that PAQR3 governs the preferential formation and activation of ATG14L‐linked VPS34 complex for autophagy initiation via two levels of regulation. Firstly, PAQR3 functions as a scaffold protein that facilitates the formation of ATG14L‐ but not UVRAG‐linked VPS34 complex, leading to elevated capacity of PI(3)P generation ahead of starvation signals. Secondly, AMPK phosphorylates PAQR3 at threonine 32 and switches on PI(3)P production to initiate autophagosome formation swiftly after glucose starvation. Deletion of PAQR3 leads to reduction of exercise‐induced autophagy in mice, accompanied by a certain degree of disaggregation of ATG14L‐associated VPS34 complex. Together, this study uncovers that PAQR3 can not only enhance the capacity of pro‐autophagy class III PI3K due to its scaffold function, but also integrate AMPK signal to activation of ATG14L‐linked VPS34 complex upon glucose starvation.

ATF4/ATG5 Signaling in Hypothalamic Proopiomelanocortin Neurons Regulates Fat Mass via Affecting Energy Expenditure

Although many biological functions of activating transcription factor 4 (ATF4) have been identified, a role of hypothalamic ATF4 in the regulation of energy homeostasis is poorly understood. In this study, we showed that hypothalamic proopiomelanocortin (POMC) neuron–specific ATF4 knockout (PAKO) mice are lean and have higher energy expenditure. Furthermore, PAKO mice were resistant to high-fat diet–induced obesity, glucose intolerance, and leptin resistance. Moreover, the expression of autophagy protein 5 (ATG5) was increased or decreased by ATF4 knockdown or overexpression, respectively, and ATF4 inhibited the transcription of ATG5 by binding to the basic zipper-containing protein sites on its promoter. Importantly, mice with double knockout of ATF4 and ATG5 in POMC neurons gained more fat mass and reduced energy expenditure compared with PAKO mice under a high-fat diet. Finally, the effect of ATF4 deletion in POMC neurons was possibly mediated via enhanced ATG5-dependent autophagy and α-melanocyte–stimulating hormone production in the hypothalamus. Taken together, these results identify the beneficial role of hypothalamic ATF4/ATG5 axis in the regulation of energy expenditure, obesity, and obesity-related metabolic disorders, which suggests that ATF4/ATG5 axis in the hypothalamus may be a new potential therapeutic target for treating obesity and obesity-related metabolic diseases.

TFEB regulates PER3 expression via glucose-dependent effects on CLOCK/BMAL1.

It has been reported that metabolites regulate circadian rhythms through direct effects on clock genes. A metabolic network involving PER3 raises the possibility that some metabolic regulators are directly involved in the mammalian clock. Here, we show that the bHLH family transcription factor TFEB regulates PER3 through the CLOCK/BMAL1 complex. In the liver, TFEB expression displays circadian rhythms. A loss of TFEB function disrupts and dampens the expression of PER3 but not the expression of other circadian genes, such as PER1, PER2, CRY1 and CRY2. TFEB physically interacts with CLOCK/BMAL1 through its N-terminal region. In the presence of TFEB, BMAL1/CLOCK-mediated transcription is enhanced. Moreover, the TFEB/CLOCK/BMAL1 complex is regulated by glucose. These results show that TFEB has a role in the mammalian clock mechanism.

The C-ETS2-TFEB Axis Promotes Neuron Survival under Oxidative Stress by Regulating Lysosome Activity

Excessive reactive oxygen species/reactive nitrogen species (ROS/RNS) produced as a result of ageing causes damage to macromolecules and organelles or leads to interference of cell signalling pathways, which in turn results in oxidative stress. Oxidative stress occurs in many neurodegenerative diseases (e.g., Parkinsons disease) and contributes to progressive neuronal loss. In this study, we show that cell apoptosis is induced by oxidative stress and that lysosomes play an important role in cell survival under oxidative stress. As a compensatory response to this stress, lysosomal genes were upregulated via induction of transcription factor EB (TFEB). In addition, localization of TFEB to the nucleus was increased by oxidative stress. We also confirmed that TFEB protects cells from oxidative stress both in vitro and in vivo. Finally, we found that C-ETS2 senses oxidative stress, activates TFEB transcription, and mediates the upregulation of lysosomal genes. Our results demonstrate a mechanistic pathway for inducing lysosomal activity during ageing and neurodegeneration.

Phosphorylation of MITF by AKT affects its downstream targets and causes TP53-dependent cell senescence

Microphthalmia-associated transcription factor (MITF) plays a crucial role in the melanogenesis and proliferation of melanocytes that is dependent on its abundance and modification. Here, we report that epidermal growth factor (EGF) induces senescence and cyclin-dependent kinase inhibitor 1A (CDKN1A) expression that is related to MITF. We found that MITF could bind TP53 to regulate CDKN1A. Furthermore, the interaction between MITF and TP53 is dependent on AKT activity. We found that AKT phosphorylates MITF at S510. Phosphorylated MITF S510 enhances its affinity to TP53 and promotes CDKN1A expression. Meanwhile, the unphosphorylative MITF promotes TYR expression. The levels of p-MITF-S510 are low in 90% human melanoma samples. Thus the level of p-MITF-S510 could be a possible diagnostic marker for melanoma. Our findings reveal a mechanism for regulating MITF functions in response to EGF stimulation and suggest a possible implementation for preventing the over proliferation of melanoma cells.

miR-27a is highly expressed in H1650 cancer stem cells and regulates proliferation, migration, and invasion

Background: Cancer stem cells (CSCs) are responsible for tumor relapse after chemotherapy and radiotherapy in non-small cell lung cancer (NSCLC). The aim of this study is to explore the profile and role of microRNA (miRNA) in CSC of NSCLC. Materials and Methods: We studied the expression of stem cell marker in side population cells and serum-free cultured spheres of NSCLC. We identified that CD133+ CD34− cells are NSCLC stem cell. We isolated CD133+ CD34− cells and CD133− CD34+ cells with MicroBead Kit. We verified that H1650 CD133+ CD34− cells have CSC characteristics with doxorubicin, radiation, and xenograft. We studied miRNA expression profile in H1650 and HCC827 CD133+ CD34− cells with microarray analysis. We detected proliferation, migration, and invasion with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, scratch test, and Transwell chamber invasion assay, respectively. Results: CD133 and CD34 are CSC markers in H1650. We demonstrated that H1650 CD133+ CD34− cells have CSC characteristics and found that miR-27a was highly expressed in H1650 CD133+ CD34− cells. In addition, we showed that miR-27a regulates proliferation, migration, and invasion in H1650 cell line and demonstrated that miR-27a expression was positively related to epidermal growth factor receptor in NSCLC cell lines. Conclusions: CD133+ CD34− is a CSC marker in H1650. miR-27a is highly expressed in H1650 CSCs and regulates cancer development in H1650. miR-27a may be a potential target for NSCLC therapy.

Oxidative Stress Induces Neuronal Apoptosis Through Suppressing Transcription Factor EB Phosphorylation at Ser467

Background/Aims: This study determined the role and mechanism of action of transcription factor EB (TFEB) in H2O2-induced neuronal apoptosis. Methods: SH-SY5Y cells were treated with Akt inhibitor/activator and different concentrations of H2O2. Cell apoptosis was detected by flow cytometric analysis. Akt and TFEB phosphorylation and PARP cleavage were determined by Western blotting. HEK293T cells were transfected with different truncated TFEB mutants and HA-Akt-WT; SH-SY5Y cells were transfected with Flag-vector, Flag-TFEB, Flag-TFEB-S467A or Flag-TFEB-S467D; and TFEB interaction with Akt was determined by co-immunoprecipitation and GST pull-down assays. Results: A low concentration of H2O2 induces TFEB phosphorylation at Ser467 and nuclear translocation, facilitating neuronal survival, whereas a high concentration of H2O2 promotes SH-SY5Y cell apoptosis via suppressing TFEB Ser467 phosphorylation and nuclear translocation. The TFEB-S467D mutant is more easily translocated into the nucleus than the non-phosphorylated TFEB-S467A mutant. Further, Akt physically binds to TFEB via its C-terminal tail interaction with the HLH domain of TFEB and phosphorylates TFEB at Ser467. Mutation of TFEB-Ser467 can prevent the phosphorylation of TFEB by Akt, preventing inhibition of oxidative stress-induced apoptosis. Conclusions: Oxidative stress induces neuronal apoptosis through suppressing TFEB phosphorylation at Ser467 by Akt, providing a novel therapeutic strategy for neurodegenerative diseases.

The influence of IMF clock angle on the cross‐section of the tail bow shock

We study effects of the interplanetary magnetic field (IMF) orientation on the terrestrial tail bow shock location and shape by using global MHD magnetosphere model and empirical bow shock models. It is shown that the tail bow shock cross section is well approximated by an ellipse with the direction of the major axis roughly perpendicular to the IMF clock angle direction. With the increasing IMF clock angle, the eccentricity of the bow shock cross section increases for northward IMF but decreases for southward IMF.