Activation of the Mitochondrial Apoptotic Signaling Platform during Rubella Virus Infection

p53 and RNA viruses: The tug of war

Host factors play essential roles in viral infection, and their interactions with viral proteins are necessary for establishing effective pathogenesis. p53 is a host factor that maintains genomic integrity by controlling cell-cycle progression and cell survival. It is a well-known tumor suppressor protein that gets activated by various stress signals, thereby regulating cellular pathways. The cellular outcomes from different stresses are tightly related to p53 dynamics, including its alterations at gene, mRNA, or protein levels. p53 also contributes to immune responses leading to the abolition of viral pathogens. In turn, the viruses have evolved strategies to subvert p53-mediated host responses to improve their life cycle and pathogenesis. Some viruses attenuate wild-type p53 (WT-p53) function for successful pathogenesis, including degradation and sequestration of p53. In contrast, some others exploit the WT-p53 function through regulation at the transcriptional/translational level to spread infection. One area in which the importance of such host factors is increasingly emerging is the positive-strand RNA viruses that cause fatal viral infections. In this review, we provide insight into all the possible mechanisms of p53 modulation exploited by the positive-strand RNA viruses to establish infection. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Regulation RNA in Disease and Development > RNA in Disease.

5,6-Dichloro-1-β-D-ribofuranosylbenzimidazole (DRB) induces apoptosis in breast cancer cells through inhibiting of Mcl-1 expression

The effective treatment of breast cancer remains a profound clinical challenge, especially due to drug resistance and metastasis which unfortunately arise in many patients. The transcription inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB), as a selective inhibitor of cyclin-dependent kinase 9, was shown to be effective in inducing apoptosis in various hematopoietic malignancies. However, the anticancer efficacy of DRB against breast cancer is still unclear. Herein, we demonstrated that administration of DRB to the breast cancer cell line led to the inhibition of cellular proliferation and induction of the typical signs of apoptotic cells, including the increases in Annexin V-positive cells, DNA fragmentation, and activation of caspase-7, caspase-9, and poly (ADP ribose) polymerase (PARP). Treatment of DRB resulted in a rapid decline in the myeloid cell leukemia 1 (Mcl-1) protein, whereas levels of other antiapoptotic proteins did not change. Overexpression of Mcl-1 decreased the DRB-induced PARP cleavage, whereas knockdown of Mcl-1 enhanced the effects of DRB on PARP activation, indicating that loss of Mcl-1 accounts for the DRB-mediated apoptosis in MCF-7 cells, but not in T-47D. Furthermore, we found that co-treatment of MCF-7 cells with an inhibitor of AKT (LY294002) or an inhibitor of the proteasome (MG-132) significantly augmented the DRB-induced apoptosis. These data suggested that DRB in combination with LY294002 or MG-132 may have a greater therapeutic potency against breast cancer cells.

Mitochondrial DNA haplogroup F confers genetic susceptibility to chronic HBV infection for the Yi nationality in Lijiang, China

Mitochondria are essential for hepatitis B virus (HBV) infection. Moreover, the findings of our previous study indicate that host mitochondrial genetic factors are associated with chronic hepatitis B (CHB) for the Han Chinese. However, in terms of genetic heterogeneity, the impact of mitochondria on host susceptibility to HBV infection in ethnic minorities in China remains unclear. Here, a total of 7070 subjects who had visited the hospital between June 1, 2019, and April 31, 2020, were enrolled for seroprevalence of HBV infection investigation. A total of 220 individuals with CHB (CHBs) and 223 individuals with a trace of HBV infection (spontaneously recovered subjects, SRs) were analyzed for mitochondrial DNA (mtDNA) sequence variations and classified into respective haplogroups. Haplogroup frequencies were compared between CHBs and SRs. Among eight nationalities, Yi nationality patients had the highest HBsAg prevalence rate (27.9% [95% CI: 25.3%-30.5%]) and the lowest vaccination rate (4.9% [95% CI: 3.7%-6.2%]). After adjustment for age and gender, haplogroup F was a risk factor for CHB infection (P = 0.049, OR = 2.079, 95% CI = 1.002-4.31), while D4 had a significant negative correlation with the HBeAg-positive rate (P = 0.024, OR = 0.215, 95% CI = 0.057-0.816). Together with our previous study, the findings indicate that different nationalities have different genetic susceptibility to HBV infection.

A Study of the Impact of Graphene Oxide on Viral Infection Related to A549 and TC28a2 Human Cell Lines

Graphene has been one of the most tested materials since its discovery in 2004. It is known for its special properties, such as electrical conductivity, elasticity and flexibility, antimicrobial effect, and high biocompatibility with many mammal cells. In medicine, the antibacterial, antiviral, and antitumor properties of graphene have been tested as intensively as its drug carrying ability. In this study, the protective effect of graphene oxide against Rubella virus infection of human lung epithelial carcinoma cells and human chondrocyte cells was examined. Cells were incubated with graphene oxide alone and in combination with the Rubella virus. The cytopathic effect in two incubation time periods was measured using DAPI dye as a percentage value of the changed cells. It was shown that the graphene oxide alone has no cytopathic effect on any of tested cell lines, while the Rubella virus alone is highly cytopathic to the cells. However, in combination with the graphene oxide percentage of the changed cells, its cytotopathicity is significantly lower. Moreover, it can be concluded that graphene oxide has protective properties against the Rubella virus infection to cells, lowering its cytopathic changes to the human cells.

Mitochondria Redistribution in Enterovirus A71 Infected Cells and Its Effect on Virus Replication

Enterovirus A71 (EV-A71) is one of the main causative agents of hand, foot and mouth disease (HFMD) and it also causes severe neurologic complications in infected children. The interactions between some viruses and the host mitochondria are crucial for virus replication and pathogenicity. In this study, it was observed that EV-A71 infection resulted in a perinuclear redistribution of the mitochondria. The mitochondria rearrangement was found to require the microtubule network, the dynein complex and a low cytosolic calcium concentration. Subsequently, the EV-A71 non-structural protein 2BC was identified as the viral protein capable of inducing mitochondria clustering. The protein was found localized on mitochondria and interacted with the mitochondrial Rho GTPase 1 (RHOT1) that is a key protein required for attachment between the mitochondria and the motor proteins, which are responsible for the control of mitochondria movement. Additionally, suppressing mitochondria clustering by treating cells with nocodazole, EHNA, thapsigargin or A23187 consistently inhibited EV-A71 replication, indicating that mitochondria recruitment played a crucial role in the EV-A71 life cycle. This study identified a novel function of the EV-A71 2BC protein and provided a potential model for the regulation of mitochondrial motility in EV-A71 infection.

Rubella Virus Strain-Associated Differences in the Induction of Oxidative Stress Are Independent of Their Interferon Activation

Rubella virus (RV) infection impacts cellular metabolic activity in a complex manner with strain-specific nutritional requirements. Here we addressed whether this differential metabolic influence was associated with differences in oxidative stress induction and subsequently with innate immune response activation. The low passaged clinical isolates of RV examined in this study induced oxidative stress as validated through generation of the reactive oxygen species (ROS) cytoplasmic hydrogen peroxide and mitochondrial superoxide. The addition of the cytoplasmic and mitochondrial ROS scavengers N-acetyl-l-cysteine and MitoTEMPO, respectively, reduced RV-associated cytopathogenicity and caspase activation. While the degree of oxidative stress induction varied among RV clinical isolates, the level of innate immune response and interferon-stimulated gene activation was comparable. The type III IFNs were highly upregulated in all cell culture systems tested. However, only pre-stimulation with IFN β slightly reduced RV replication indicating that RV appears to have evolved the ability to counteract innate immune response mechanisms. Through the data presented, we showed that the ability of RV to induce oxidative stress was independent of its capacity to stimulate and counteract the intrinsic innate immune response.

Alterations in Cell Mechanics by Actin Cytoskeletal Changes Correlate with Strain-Specific Rubella Virus Phenotypes for Cell Migration and Induction of Apoptosis

The cellular cytoskeleton is central for key cellular functions, and as such is a marker for diseased and infected cell states. Here we analyzed infection with rubella virus (RV) strains with respect to phenotypes in cellular mechanical properties, cell movement, and viral cytopathogenicity. Real-time deformability cytometry (RT-DC), as a high-throughput platform for the assessment of cell mechanics, revealed a correlation of an increase in cortical filamentous-actin (F-actin) with a higher cellular stiffness. The additional reduction of stress fibers noted for only some RV strains as the most severe actin rearrangement lowered cell stiffness. Furthermore, a reduced collective and single cell migration speed in a wound healing assay was detected in addition to severe changes in cell morphology. The latter was followed by activation of caspase 3/7 as a sign for induction of apoptosis. Our study emphasizes RT-DC technology as a sensitive means to characterize viral cell populations and to implicate alterations of cell mechanical properties with cell functions. These interdependent events are not only promising options to elucidate viral spread and to understand viral pathologies within the infected host. They also contribute to any diseased cell state, as exemplified by RV as a representative agent for cytoskeletal alterations involved in a cytopathological outcome.

Correlations between mitochondrial DNA haplogroup D5 and chronic hepatitis B virus infection in Yunnan, China

Mitochondrial abnormality is frequently reported in individuals with hepatitis B virus (HBV) infection, but the associated hosts’ mitochondrial genetic factors remain obscure. We hypothesized that mitochondria may affect host susceptibility to HBV infection. In this study, we aimed to detect the association between chronic HBV infection and mitochondrial DNA in Chinese from Yunnan, Southwest China. A total of 272 individuals with chronic HBV infection (CHB), 310 who had never been infected by HBV (healthy controls, HC) and 278 with a trace of HBV infection (spontaneously recovered, SR) were analysed for mtDNA sequence variations and classified into respective haplogroups. Haplogroup frequencies were compared between HBV infected patients, HCs and SRs. Haplogroup D5 presented a higher frequency in CHBs than in HCs (P = 0.017, OR = 2.87, 95% confidence interval [CI] = (1.21–6.81)) and SRs (P = 0.049, OR = 2.90, 95% CI = 1.01–8.35). The network of haplogroup D5 revealed a distinct distribution pattern between CHBs and non-CHBs. A trend of higher viral load among CHBs with haplogroup D5 was observed. Our results indicate the risk potential of mtDNA haplogroup D5 in chronic HBV infection in Yunnan, China.

Infection of iPSC Lines with Miscarriage-Associated Coxsackievirus and Measles Virus and Teratogenic Rubella Virus as a Model for Viral Impairment of Early Human Embryogenesis

Human induced pluripotent stem cell (iPSC) lines are a promising model for the early phase of human embryonic development. Here, their contribution to the still incompletely understood pathogenesis of congenital virus infections was evaluated. The infection of iPSC lines with miscarriage-associated coxsackievirus B3 (CVB3) and measles virus (MV) was compared to the efficient teratogen rubella virus (RV). While CVB3 and MV were found to be cytopathogenic on iPSC lines, RV replicated without impairment of iPSC colony morphology and integrity. This so far outstanding course of infection enabled maintenance of RV-infected iPSC cultures over several passages and their subsequent differentiation to ectoderm, endoderm, and mesoderm. A modification of the metabolic profile of infected iPSC lines was the only common aspect for all three viruses. This study points toward two important aspects. First, iPSC lines represent a suitable cell culture model for early embryonic virus infection. Second, metabolic activity represents an important means for evaluation of pathogen-associated alterations in iPSC lines.

Icarisid II inhibits the proliferation of human osteosarcoma cells by inducing apoptosis and cell cycle arrest

Icarisid II, one of the main active components of Herba Epimedii extracts, shows potent antitumor activity in various cancer cell lines, including osteosarcoma cells. However, the anticancer mechanism of icarisid II against osteosarcoma U2OS needs further exploration. This study aims to investigate further antitumor effects of icarisid II on human osteosarcoma cells and elucidate the underlying mechanism. We cultivated human osteosarcoma USO2 cells in vitro using different concentrations of icarisid II (0-30 µM). Cell viability was detected at 24, 48, and 72 h using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis. Cell cycle was tested by flow cytometry after treatment with icarisid II for 48 h. Annexin V-allophycocyanin and 7-aminoactinomycin D staining were conducted to detect cell apoptosis. Quantitative real-time polymerase chain reaction and Western blot assay were performed to measure the levels of genes and proteins related to cell cycle and apoptosis. Results showed that icarisid II significantly inhibited the proliferation and induced apoptosis of human osteosarcoma U2OS cells. The half maximal inhibitory concentration values were 14.44, 11.02, and 7.37 µM at 24, 48, and 72 h, respectively. Cell cycle was arrested in the G2/M phase in vitro. In addition, icarisid II upregulated the expression levels of P21 and CyclinB1 whereas downregulated the expression levels of CyclinD1, CDC2, and P-Cdc25C, which were related to cell cycle arrest in U2OS cells. The cell apoptotic rate increased in a dose-dependent manner after treatment with icarisid II for 48 h. Icarisid II induced apoptosis by upregulating Bax, downregulating Bcl-2, and activating apoptosis-related proteins, including cleaved caspase-3, caspase-7, caspase-9, and poly (ADP-ribose) polymerase. These data indicate that icarisid II exhibits an antiproliferation effect on human osteosarcoma cells and induces apoptosis by activating the caspase family in a time- and dose-dependent manner in vitro. Therefore, icarisid II may be used as a candidate agent for the clinical treatment of osteosarcoma in the future.

Molecular and immune response characterizations of a novel AIF and cytochrome c in Litopenaeus vannamei defending against WSSV infection

Apoptosis inducing factor (AIF) and cytochrome c (CYC) are two mitochondrial apoptogenic factors. In the present study, the cDNA sequences of AIF (LvAIF) and CYC (LvCYC) were cloned from Pacific white shrimp, Litopenaeus vannamei. The LvAIF was 1664 bp, including a 5'-terminal untranslated region (UTR) of 154 bp, an open reading frame (ORF) of 1323 bp encoding a polypeptide of 440 amino acids (aa) and a 3' UTR of 187 bp. The LvCYC was 582 bp, including a 50 bp 5' UTR, a 315 bp ORF encoding for 104 aa, and a 217 bp 3' UTR. The deduced protein of LvAIF contained a conserved Pyr_redox and AIF_C domain at the N-terminal and the predicted LvCYC included a conservative cytochrome_C domain, respectively. Phylogenetic analysis revealed that LvAIF belonged to AIF1 subfamily and showed a close relationship with AIF1 from vertebrates and LvCYC showed the closest relationship with its counterparts from shrimp Marsupenaeus japonicus. Tissue expression profiles showed that both LvAIF and LvCYC existed in most tissues, with the most predominant expression of LvAIF in intestine, then followed muscle and the weakest expression in gill. The highest expression of LvCYC was detected in muscle, and the weakest expression was in hemocytes. Additionally, after white spot syndrome virus (WSSV) infection, the significant up-regulation of LvAIF, LvCYC and caspase 3 transcripts and the increase of pro-caspase 3 and active-caspase 3 protein were detected at most time points (P < 0.05). However, all of the three genes down-regulated in hemocytes in the early stage after WSSV infection. WSSV proliferation and shrimp mortality showed a time-dependent manner and the production of ROS in hemocytes were significantly increased at 6 and 24 h after infection. Our results showed that the apoptotic genes AIF, CYC and caspase 3 might play crucial roles in hepatopancreas, however, the production of ROS in hemocytes might be important in shrimp defense against WSSV infection.