Background
Dengue virus (DENV) is a positive-sense, single-stranded RNA virus with a diameter of 50 nm. It is approximately 11 kd long and belongs to the
Flavivirus genus, Flaviviridae. Humans are generally susceptible to DENV and are a natural DENV host [
1]. According to statistics, ~ 3.6 billion people are at risk worldwide [
2,
3] and more than 21,000 people die each year. Thus, DENV infection has become a major public health problem of global concern. DENV has four serotypes, i.e., DENV1–4, of which DENV-2 is the most widely transmitted [
4]. The main spreading process of DENV is relatively simple. After a female mosquito feeds on the blood of a DENV patient, DENV multiplies in the mosquito body and spreads to susceptible individuals through mosquito bites [
5]. DENV infection causes several self-limiting febrile diseases including dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). DHF and DSS are fatal syndromes with clinical manifestations of increased vascular permeability and plasma leakage [
6], and further result in multiple organ damage and circulatory system failure, which endangers life [
7‐
9]. Pathogenesis is associated with the dysfunction of vascular endothelial cells and autophagy. Autophagy is activated by DENV infection to prevent the fusion of autophagosomes with lysosomes. DENV replicates, assembles, and matures in autophagosomes, thus evading neutralizing antibodies during transport [
10,
11].
Autophagy is a lysosomal-dependent degradation pathway in eukaryotic cells that regulates intracellular homeostasis and affects innate immune mechanisms by modulating pattern-recognition receptors and signal transduction associated with injury-related molecular patterns. Thus, intracellular pathogens (e.g., viruses and bacteria) may be specifically recognized and quickly targeted to the autophagy degradation pathway [
12,
13]. Recent studies have shown that DENV-2-induced autophagy exhibits a protective effect on infected cells. Denv-2 activates the autophagy pathway to increase the replication of its RNA, whereas the inhibition of autophagy results in a significant decrease in viral replication [
14,
15]. DENV can induce vascular leakage through macrophage migration inhibitor factor secretion and autophagy formation. Infectious autophagy-associated DF vesicles released by DENV-infected cells can protect viral RNA in vesicles and avoid antibody neutralization to promote viral transmission [
11]. Previous work indicated that DENV-2 can induce primary human umbilical vein endothelial cells (HUVECs) to induce autophagy through the adenosine monophosphate-activated protein kinase (AMPK)/extracellular signal-regulated kinase (ERK)/mammalian target of rapamycin (mTOR) signaling pathway [
16]. However, the mechanism through which DENV-2 activates tuberous sclerosis complex 2 (TSC2) via the AMPK and ERK1/2 pathways causing mTOR inhibition is unclear.
Tripartite motif-containing 22 (TRIM22), also known as Staf50, is an interferon-stimulated gene. Previous studies showed that the TRIM protein family is involved in a wide range of cellular processes, including apoptosis, cell cycle progression, and autophagy [
17]. Autophagy is regulated by TRIM22 and has both antiviral and viral replication effects. On the one hand, TRIM22 promotes GEM-induced prosurvival autophagy and protects non-small cell lung cancer (NSCLC) cells from apoptosis [
18]. TRIM22 promotes viral replication by regulating autophagy. Related studies have demonstrated that TRIM22 binds with the autophagy-related proteins, unc-51-like autophagy activating kinase 1 (ULK1), and Beclin1 to induce autophagy, thus promoting the replication of the respiratory syncytial virus (RSV) [
19]. The preliminary proteomics results of the current study demonstrated that TRIM22 protein expression significantly increased 36 h after HUVECs were infected with DENV-2. A protein–protein interaction analysis in the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database revealed that TRIM22 was associated with the AMPK/ERK/mTOR signaling pathway. Therefore, whether TRIM22 is involved in autophagy activation of DENV-2-infected HUVECs through the AMPK/ERK/mTOR pathway remains to be determined. Based on these findings, the mechanism of autophagy induced by the activation of the AMPK/ERK/mTOR signaling pathway following DENV-2 infection was explored. Determining how DENV-2 induces HUVEC autophagy through relevant signal transduction pathways will contribute to the development of effective immunotherapies and appropriate chemical drugs. In addition, this will provide an important theoretical basis for better understanding the pathogenic mechanism(s) of viral infection and lead to the development of antiviral drugs that target autophagy.
Materials and methods
Cell strain
The Denv-2 standard strain (NGC strain) was preserved in liquid nitrogen. HUVECs were purchased from ScienCell (Carlsbad, CA, USA). Aedes albopictus cells (C6/36) were purchased from the Kunming Cell Bank of the Chinese Academy of Sciences (Kunming, China). TOP10 competent Escherichia coli cells were purchased from the TIANGEN Company (Beijing, China).
Plasmid
Br-v108 vectors (AgeI and EcoRI restriction enzyme cutting sites) were purchased from Shanghai Jikai Gene Technology Co., Ltd. (Shanghai, China). Lv-007 vectors (NheI and AgeI restriction enzyme cutting sites) were purchased from YBR BioSCI Res (Shanghai, China).
Reagents and instruments
Extracellular matrix (ECM) media were purchased from ScienCell. RPMI-1640 media was purchased from Gibco (Thermo Fisher Scientific, Waltham, MA, USA). Trizol was purchased from Sigma-Aldrich (Sigma-Aldrich, Burlington, MA, USA). Hiscript QRT Supermix for quantitative PCR (qPCR) and AceQ qPCR SYBR Green was purchased from Vazyme (Nanjing, China). Antibodies (TRIM22, Beclin1, P62, ATG7, ATG5, mTOR, P-mTOR, AMPK, P-AMPK, ERK, P-ERK, and GAPDH) were purchased from Abcam (Abcam, Cambridge, UK). Age I and EcoRI were purchased from NEB (New England Biolabs, Ipswich, MA, USA). The BCA Protein Assay Kit was purchased from HyClone-Pierce, Inc (Thermo Fisher Scientific). Real-time fluorescence quantitative polymerase chain reaction (PCR) was purchased from ABI (StepOne PLUS, Thermo Fisher Scientific). The gel imager was purchased from Bio-Rad (Bio-Rad, Hercules, CA, USA). The ultraviolet–visible spectrophotometer was purchased from Thermo Fisher Scientific. The chemiluminescence imaging system used was a GE AI600. The microplate reader was purchased from Bio-Rad.
Cell culture and identification
HUVECs stored in liquid nitrogen were removed and thawed in a 37 °C water bath. HUVECs were transferred to a T25 cm2 flask containing 5 mL of ECM complete culture solution (10% FBS, 1% ECGs, and 1% P/S) at 37 °C with 5% CO2. Cell growth was observed each day after HUVECs had adhered to the wall. The growth density of the HUVECs was 80–90% for subculture. The subculture conditions were 28 °C with 5% CO2 and ECM complete culture solution was the culture medium. When specific molecules, vWF/Factor VIII and CD31, were identified as positive by immunofluorescence, and HIV-1, HBV, HCV, mycoplasma, bacteria, yeast, and fungi were identified as negative, the first generation was cryopreserved when the number of cells was greater than 5 × 105/mL. In this laboratory, subculture was continued to the fourth generation for the experiments.
DENV-2 virulence test
Aedes albopictus cells (C6/36) were recovered, cultured, and subcultured. At the logarithmic growth stage (density, 80–90%), the cells were seeded into 96-well plates and cultured at 28 °C in a 5% CO2 atmosphere overnight. HUVECs stored in liquid nitrogen were removed and quickly thawed in a 37 °C water bath. The virus stock was diluted tenfold with an RPMI-1640 maintenance solution. Eight concentrations (10−3–10−10) and eight wells for each concentration were noted. The blank control was established and different dilutions of disease venom were simultaneously added and incubated at 37 °C with 5% CO2 for 2 h. The supernatant was discarded, the cells were washed with Hank’s solution, and a fresh medium (200 μL/well) was added. The culture was continued and cytopathic conditions were observed and recorded. The number of lesion holes at each dilution level was recorded and counted within 5 days and the Reed–Muench method was used to calculate the toxicity of DENV-2 to C6/36.
DENV-2 infects HUVECs
HUVECs were recovered, cultured, and subcultured. The cells were seeded into six-well plates and cultured at 37 °C with 5% CO2 overnight at the logarithmic growth stage (density, 80–90%). DENV-2 was stored in liquid nitrogen, removed, and quickly thawed in a 37 °C water bath. The original virus solution was diluted 103, 104, and 105 times with maintenance solution, and the blank control was established. The diluted disease venom was added and incubated at 37 °C with 5% CO2 for 2 h. The flask was shaken every 30 min to evenly distribute the venom. The supernatant was discarded and the cells were washed twice with Hank’s wash solution. A maintenance solution was added and the culture was continued for 36 h. Total protein from cells in the experimental and blank groups was collected.
TEM detection of HUVEC autophagosomes
HUVECs were infected with DENV-2 virus stock solution, which was diluted 105 times. Simultaneously, the blank control was set at 37 °C with 5% CO2 and the cells were collected at 24 and 36 h. The cells were analyzed by electron microscopy at the Chongqing Medical University after fixing with 2.5% glutaraldehyde. The ultrastructure of the cells was observed by TEM and imaged after dehydration, resin soaking, embedding, sectioning, and staining.
TRIM22 gene RNA interference interferes with plasmid vector construction
Using the TRIM22 gene as a template, three RNA interference target sequences were designed and an RNA interference lentiviral vector was constructed. shTRIM22-1, shTRIM22-2, and shTRIM22-3 represent the knockdown shRNA targets at three different sites designed for the TRIM22 gene. shRNA interference sequences were designed following the selected target sequences, and appropriate restriction enzyme sites were included at both ends. A double-stranded DNA oligo was prepared and linearized by Age I and EcoR I double digestion of the BR-V108 vector, ligated into the linearized vector, and transformed into TOP10-competent E. coli cells by heat shock. After screening, monoclonal expansion culture was conducted, the bacterial fluid was collected, and the plasmid was isolated using the Zyokang GTC endotoxin-free plasmid extraction kit. The plasmid concentration was measured using a microspectrophotometer. The plasmid was identified by 1% agarose gel electrophoresis after PCR amplification.
Construction of a TRIM22 gene-overexpressing lentiviral vector
The lV-007 vector was linearized by Nhe I and Age I double digestion. The target gene fragment was amplified by PCR. The homologous recombination sequence was added to the 5′ end of the amplimer, and the 5′- and 3′-terminal sequences of the amplified product matched that of the linearized clone vector. The linearized vector and the target gene fragment were recombined in vitro. The recombinant plasmid was transformed into the recipient cell, and individual clones were selected for identification by PCR and DNA sequencing. The positive clones were expanded and extracted to obtain plasmid with high purity.
Lentivirus infection of HUVECs
HUVECs in the logarithmic phase (cell density reaching 80–90%) were divided into an shCtrl group (lentivirus empty vector transfection group, as negative control, NC control group) and an shTRIM22 group (TRIM22 knockdown group). The cells (1 × 105) were inoculated cells into six-well plates and supplemented with EMC complete culture medium to 2 mL. The plates were mixed and incubated at 37 °C with 5% CO2 for 24 h. The supernatants were discarded and 1 mL of opti-MEM serum-free medium was added to each well. NC control virus and TRIM22 knockdown virus were added at 108 TCID50/mL, shaken, and incubated at 37 °C with 5% CO2 for 18 h. The supernatant was discarded and 2 mL of ECM complete culture medium was added to each well for 48 h. The fluorescence intensity and infection efficiency were assessed by fluorescence microscopy.
Quantitative real-time PCR detection
Total RNA was extracted using Trizol from the NC control virus infected with DENV-2 and HUVECs treated with TRIM22 knockdown virus during the logarithmic growth period. The concentration and purity of RNA were measured using an ultramicro-ultraviolet-visible spectrophotometer, and cDNA was obtained by reverse transcription using the RNA as a template. The expression of the target genes was measured by SYBR Green-based qPCR. The procedure was as follows: predenaturation at 95 °C for 1 min, denaturation at 95 °C for 10 s, annealing at 60 °C for 30 s, and repetition of this program for 40 cycles. A melt curve was also established for each gene. Relative quantitative analysis
F = 2
−△△Ct was used, where △Ct represents the Ct value of the target gene minus the Ct value of the reference gene, − △△Ct is the average value of △Ct in the group C–△Ct value of each sample. In addition, 2
−△△Ct reflects the relative expression level of target genes in each sample compared with the NC group. GAPDH expression was used as an internal reference. The primiers used refer to Table
1.
Table 1
Sequence of correlated primers for experiments
P62 | F: GCAATGGGCCTGTGGTAG | 191 |
R: CCCGAAGTGTCCGTGTTT |
ATG7 | F: GTTGTTTGCTTCCGTGAC | 142 |
R: TGCCTCCTTTCTGGTTCT |
ATG5 | F: AAGCAACTCTGGATGGGATT | 173 |
R: GCAGCCACAGGACGAAAC |
TRIM22 | F: GAGATGTCTGTGAGCACCAT | 136 |
R: TCCTTGACCACCTCGTTT |
Beclin1 | F: CGTGGAATGGAATGAGAT | 110 |
R: CGTAAGGAACAAGTCGGTAT |
ERK | F: TGTTCCCAAATGCTGACT | 131 |
R: GGGTCGTAATACTGCTCC |
AMPK | F: CCGAGAAGCAGAAACACG | 167 |
R: CACATCAAGGCTCCGAAT |
mTOR | F: GCTGTCATCCCTTTATCG | 100 |
R: TCTTCTTCTTCTCCCTGTAGTC |
GAPDH | F: TGACTTCAACAGCGACACCCA | 121 |
R: CACCCTGTTGCTGTAGCCAAA |
Cell cycle assay
HUVECs in the logarithmic growth stage were counted and the cells were seeded into six-well plates and cultured with NC control virus and TRIM22 knockdown virus at 108 TCID50/mL. After the cells of the HUVEC NC and TRIM22 knockdown groups reached 90%, 300 μL of ECM medium was added to each well to prepare a cell suspension. The cells were collected in 5 mL centrifuge tubes with three wells per group. After centrifugation at 300 g for 5 min, the supernatant was discarded and the propidium iodide staining solution was added to resuspend the cells. The cells were analyzed by flow cytometry (FCM) after incubating in the dark for 20 min.
CCK8 assay for cell proliferation
HUVECs were seeded into six-well plates and cultured with NC control and TRIM22 knockdown viruses at 108 TCID50/mL. After cell fusion, the HUVEC NC and TRIM22 knockdown groups were cultured to a density of 90% and counted. The NC and TRIM22 knockdown groups were then inoculated into 96-well plates at 5 × 103 cells/100 μL with three wells for each group. Next, 10 μL of CCK8 solution was added to each well, mixed, and incubated at 37 °C with 5% CO2 for 4 h. The absorbance at 450 nm was measured with a microplate reader and the experimental data were recorded.
Cell apoptosis
HUVECs were seeded into six-well plates and cultured with NC control and TRIM22 knockdown viruses at 108 TCID50/mL. After the cells reached 90% confluence, the cell suspensions were collected, centrifuged at 300 g for 3 min, and resuspended with 1 mL of 1 × binding buffer. Then, 5 μL of Annexin V-APC dye was added to each tube and mixed gently, followed by the addition of 10 μL of PI dye. The cells were analyzed within 1 h by FCM after incubating for 20 min on ice at room temperature without light.
Western blot analysis
Cells in the logarithmic phase were collected from each group and washed twice with Hank’s solution. The residual solution was discarded, and the cells were lysed in RIPA buffer (PMSF:RIPA = 1:100) containing protease and phosphoprotease inhibitors. The cells were shaken and lysed on ice, scraped off at 4 °C, and centrifuged at 12,000 rpm for 30 min. The supernatant was transferred to 1.5 mL centrifuge tubes and the concentration of each protein sample was measured by the BCA method. A 5× protein loading buffer was added to 40 μg of total protein for each sample. The proteins were separated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis at 80 V for 20 min followed by 120 V for 100 min. Following the transfer, the PVDF membranes were blocked with 5% skim milk for 120 min and incubated with primary antibody overnight. TBST was used to wash the membranes six times for 5 min each. The secondary antibody was added and incubated at room temperature for 120 min on a shaking table. After chemiluminescent detection, Image J software was used to analyze the relative amount of each protein band. The additional file
1 provided is the original data of Western Blot, and these results have been show in Figs.
8,
9,
13,
14,
17,
18 respectively.
Statistical analysis
The experimental data were analyzed by Statistical Product and Service Solutions 25.0 (SPSS25.0). All experiments were repeated at least three times. The data were plotted using GraphPad Prism 8.0 software. The data that conformed to a normal distribution were expressed as the mean ± standard deviation \(\left( {\overline{{\text{X}}} \pm {\text{s}}} \right)\). One-way analysis of variance was used for comparisons between groups, and a Student’s t-test was used for pairwise comparison. P < 0.05 was considered statistically significant.
Discussion
In recent years, studies have suggested that DENV induces autophagy to prevent host cell death and enhance viral replication. Activation of autophagy regulates lipid metabolism and provides materials and energy for DENV replication, whereas inhibition of autophagy results in a significant decrease in viral replication [
14,
15]. Previous studies showed that DENV-2-infected HUVECs induced autophagy through the AMPK/ERK/mTOR signaling pathway; however, which host cell molecules are activated by DENV-2 to regulate AMPK and ERK1/2 signaling is unclear. Therefore, the mechanism of DENV-2 activation of the AMPK/ERK/mTOR signaling pathway was examined to induce autophagy at the host protein level.
TRIM22 belongs to the TRIM protein family, which contains ~ 80 members. It is characterized as an N-terminal RING domain, one or two B-box domains, and a curly helix domain. Of these, the RING domain exhibits E3 ubiquitin ligase activity, whereas the B-box and curly helix domain mediate protein–protein interactions [
20]. Members of the TRIM family are involved in various biological processes including cell cycle regulation, autophagy, antiviral immunity, tumorigenesis, and tumor progression [
21]. TRIM22 expression may be induced by interferon and its 5′ flanking region gene contains two homologous sequences of IFN-stimulated response elements, which bind to IFN regulatory factor 1 in response to types I and II IFN stimulation and induce TRIM22 expression [
22]. In addition to interferon, TRIM22 expression is also regulated by viruses and viral antigens [
23]. As a member of the TRIM family, TRIM22 regulates viral infection through various mechanisms. Since its discovery, TRIM22 is characterized by its ability to inhibit HIV-1 transcription. TRIM22 inhibits basic HIV-1 transcription by preventing Sp1 from binding to the HIV-1 promoter, thus inhibiting HIV-1 infection [
24]. The binding of TRIM22 to the influenza virus nuclear protein promotes its downregulation through ubiquitination degradation and plasmosome dependence to inhibit influenza virus replication [
25]. TRIM22 also inhibits herpes simplex viruses by promoting chromatin compression to silence viral DNA encoding early viral genes [
26]. TRIM22 also inhibits hepatitis B virus and gamma herpesvirus [
27]. Recent studies showed that the TRIM protein family is also involved in DENV infection. TRIM69 degrades Lys104 amino acid residues of DENV NS3 by ubiquitinating its RING domain through E3 ubiquitin ligase activity to inhibit DENV replication [
28]. The subgenomic RNA of DENV-2 inhibits RIG-I activation and IFN expression by binding to TRIM25 [
29].
Autophagy is a highly conserved intracellular catabolic process and abnormal autophagy is closely associated with the occurrence and development of various diseases [
30]. Several studies have demonstrated that TRIM family members can regulate autophagy through various pathways, including the regulation of autophagy-related signaling pathways and autophagy core molecules as autophagy substrate recognition receptors [
31]. Related studies have indicated that TRIM5α promotes the initiation of autophagy by promoting the interaction between activated ULK1 and Beclin1 [
32]. TRIM39 knockdown enhances the accumulation of autophagosomes and promotes autophagic flux in a Rab7-dependent manner [
33]. TRIM65 knockdown inhibits autophagy of A549/DDP cells through the miR-138-5P/ATG7 pathway [
34], whereas TRIM14 promotes autophagy in gastric cancer cells by activating the AMPK pathway [
35].
Autophagy plays a dual role in viral infection. It inhibits viral replication and can also be exploited by the virus to promote its replication [
36]. Viruses that are cleared by autophagy include herpes simplex virus type I, sindbis virus, and human immunodeficiency virus type I. Viruses that utilize autophagy to promote their replication include Coxsackie virus B3, hepatitis C virus, and Zika virus [
34,
36]. Similarly, DENV induces autophagy to prevent host cell death and enhance its viral replication. In addition, activation of autophagy regulates lipid metabolism and provides the energy and materials for DENV replication, while inhibition of autophagy leads to a significant decrease in viral replication [
11,
14]. During viral infection, the TRIM family regulates virus–host cell interactions by regulating autophagy. Several mechanisms involving TRIM proteins in virus-induced autophagy have been reported. Some TRIM proteins act as specific substrate receptors that directly recognize viral components, which they target to mediate autophagic degradation. Some TRIM proteins regulate the activity of key signaling proteins involved in various steps of the autophagy pathway [
37]. TRIM5α not only directly recognizes the HIV capsid protein to mediate its autophagic degradation but also promotes the degradation of the HIV capsid protein by regulating autophagy-related molecules [
38]. TRIM16 promotes antiviral autophagy by promoting the activation of the P62-NRF2 axis [
39]. TRIM23 mediates virus-induced autophagy by activating TANK-bound kinase 1 (TBK1) [
40]. Similar studies indicate that TRIM22 can also regulate autophagy. TRIM22 regulates macrophage autophagy through NF-κB/Beclin1 signaling [
17], promotes GEM-induced prosurvival autophagy, and protects NSCLC cells from apoptosis [
18]. TRIM22, however, promotes viral replication by regulating autophagy. Related studies have shown that TRIM22 binds to the autophagy-related proteins, ULK1 and Beclin1, to induce autophagy, thus promoting RSV replication [
19].
Based on the above findings and previous proteomics results, the current study hypothesized that TRIM22 may be involved in the autophagic regulation of HUVECs infected with DENV-2. The present study first determined the virulence of DENV-2 and the optimal concentration required to induce HUVEC autophagy. TRIM22 expression was increased in DENV-2-infected HUVECs, confirming the previous proteomic results. TRIM22 was also knocked down in HUVECs causing the proliferation rate to decrease, the expression of autophagy-related proteins to decrease, and autolysosomes to increase. This suggests that TRIM22 knockdown inhibits autophagy, which is consistent with previous reports that TRIM22 promotes autophagy. Moreover, following TRIM22 knockdown, protein phosphorylation levels of AMPK and ERK decreased, whereas that of mTOR increased. Previous studies showed that AMPK/ERK/mTOR signaling pathway plays a key role in the regulation of autophagy, and its main mechanism is that AMPK regulates autophagy by inhibiting downstream mTOR, which may be an activation mode of AMPK/ERK/mTOR signal in the regulation of autophagy [
41‐
43]. These results suggest that TRIM22 activates autophagy through the AMPK/ERK/mTOR signaling pathway. TRIM22 induces autophagy in HUVECs through the AMPK/ERK/mTOR signaling pathway.
To determine whether TRIM22 plays a role in regulating autophagy following DENV-2 infection of HUVECs, the current study examined DENV-2-infected HUVECs with TRIM22 knockdown. HUVECs in the G2 phase of the cell cycle increased, apoptosis increased, autophagy-related protein levels decreased, and the number of autolysosomes increased. This indicates that an effect on TRIM22 on HUVEC autophagy occurs during DENV-2 infection. Moreover, TRIM22 knockdown during DENV-2 infection ameliorates the activation effect of an autophagy activator on HUVEC autophagy. These results suggest that TRIM22 promotes autophagy induced by HUVECs infected with DENV-2. Autophagy and apoptosis control intracellular homeostasis. In general, autophagy blocks the induction of apoptosis, enabling cells to adapt to environmental stress. Both processes are under the control of multiple common upstream signals, and cross-regulation exists between them as a form of inhibition [
44]. Therefore, TRIM22 knockdown results in increased HUVECs in the G2 phase of the cell cycle and increased apoptosis may be caused by autophagy inhibition. To confirm the regulation of TRIM22 on autophagy, TRIM22 was overexpressed in HUVECs and infected with DENV-2. The results indicated that autophagy increased and TRIM22 overexpression reduced the inhibitory effect of autophagy inhibitors on autophagy. The increased expression of TRIM22 during DENV-2 infection was confirmed to promote HUVEC autophagy. TRIM22 was knocked down and overexpressed in HUVECs followed by infection with DENV-2 to further explore whether TRIM22 mediates DENV-2-induced autophagy through the AMPK/ERK/mTOR pathway. Following TRIM22 knockdown, protein phosphorylation levels of AMPK and ERK decreased, whereas that of mTOR increased. In addition, the positive regulatory effect of an autophagy activator on the AMPK/ERK/mTOR pathway decreased by TRIM22 knockdown. In contrast, activation of the AMPK/ERK/mTOR pathway increased after TRIM22 overexpression, and the negative regulatory effect of autophagy inhibitors on the AMPK/ERK/mTOR pathway was reduced as a result of TRIM22 overexpression. This indicates that TRIM22 is involved in the autophagy activation of DENV-2-infected HUVECs through the AMPK/ERK/mTOR pathway.
This study confirmed, for the first time, that TRIM22 is involved in DENV-2-induced autophagy through the AMPK/ERK/mTOR signaling pathway; however, the details of this regulatory mechanism remain to be defined. Future studies will explore the mechanism through which DENV-2 promotes TRIM22 expression and the relationship between TRIM22 and the AMPK pathway to better understand the mechanism of DENV-2-induced autophagy.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.