DCAF1 inhibits the NF-κB pathway by targeting p65

Anaplasma phagocytophilum AFAP targets the host nucleolus and inhibits induced apoptosis

Anaplasma phagocytophilum, the etiologic agent of human granulocytic anaplasmosis (HGA), is an obligate intracellular Gram-negative bacterium. During infection, A. phagocytophilum transfers its type IV secretion system (T4SS) effector proteins into host cells to manipulate cellular processes. AFAP (an actin filament-associated Anaplasma phagocytophilum protein) was identified as a T4SS effector protein and found to interact with the host nucleolin, as described in a previous study. In this study, proteomic analysis was performed to extensively identify AFAP-interacting proteins in host cells and analyze the potential role of AFAP in modulating host cellular processes. A total of 586 host proteins were identified interacting with AFAP by data-independent acquisition mass spectrometry and annotated to 501 Gene Ontology (GO) terms, with the significantly over-represented ones related to ribosomes, nucleolus, DNA binding, and rRNA metabolic process. Given the role of the nucleolus in cellular stress response, the targeting of AFAP to the nucleolus, and the identification of dozens of AFAP-interacting proteins that were annotated to the GO term (GO:0072331, signal transduction by p53 class mediator), the role of AFAP in modulating host apoptosis was determined. AFAP was found capable of inhibiting induced apoptosis. Thus, the proteomic analysis of AFAP-interacting proteins and determination of AFAP with anti-apoptotic activity may help elucidate the role of this T4SS effector protein in HGA pathogenesis.

DOT1L/H3K79me2 represses HIV-1 reactivation via recruiting DCAF1

DOT1L mediates the methylation of histone H3 at lysine 79 and, in turn, the transcriptional activation or repression in a context-dependent manner, yet the regulatory mechanisms and functions of DOT1L/H3K79me remain to be fully explored. Following peptide affinity purification and proteomic analysis, we identified that DCAF1-a component of the E3 ligase complex involved in HIV regulation-is associated with H3K79me2 and DOT1L. Interestingly, blocking the expression or catalytic activity of DOT1L or repressing the expression of DCAF1 significantly enhances the tumor necrosis factor alpha (TNF-α)/nuclear factor κB (NF-κB)-induced reactivation of the latent HIV-1 genome. Mechanistically, upon TNF-α/NF-κB activation, DCAF1 is recruited to the HIV-1 long terminal repeat (LTR) by DOT1L and H3K79me2. Recruited DCAF1 subsequently induces the ubiquitination of NF-κB and restricts its accumulation at the HIV-1 LTR. Altogether, our findings reveal a feedback modulation of HIV reactivation by DOT1L-mediated histone modification regulation and highlight the potential of targeting the DOT1L/DCAF1 axis as a therapeutic strategy for HIV treatment.

Enhanced NF-κB activation via HIV-1 Tat-TRAF6 cross-talk

The Tat proteins of HIV-1 and simian immunodeficiency virus (SIV) are essential for activating viral transcription. In addition, Tat stimulates nuclear factor κB (NF-κB) signaling pathways to regulate viral gene expression although its molecular mechanism is unclear. Here, we report that Tat directly activates NF-κB through the interaction with TRAF6, which is an essential upstream signaling molecule of the canonical NF-κB pathway. This interaction increases TRAF6 oligomerization and auto-ubiquitination, as well as the synthesis of K63-linked polyubiquitin chains to further activate the NF-κB pathway and HIV-1 transcription. Moreover, ectopic expression of TRAF6 significantly activates HIV-1 transcription, whereas TRAF6 knockdown inhibits transcription. Furthermore, Tat-mediated activation of NF-κB through TRAF6 is conserved among HIV-1, HIV-2, and SIV isolates. Our study uncovers yet another mechanism by which HIV-1 subverts host transcriptional pathways to enhance its own transcription.

Monacolin K Induces Apoptosis of Human Glioma U251 Cells by Triggering ROS-Mediated Oxidative Damage and Regulating MAPKs and NF-κB Pathways

Monacolin K (MK), a polyketo secondary metabolic compound of the mold genus Monascus, can promote the apoptosis of malignant cancer cells, possessing potential antitumor properties. However, its mechanism of action on gliomas remains unclear. Here, we explored and investigated the potential of the monacolin K's antitumor effect on human glioma U251 cells and its possible molecular mechanism. Results showed that the application of 10 μM monacolin K inhibited the proliferation of U251 cells, with an inhibitory rate of up to 53.4%. Additionally, monacolin K induced the generation of reactive oxygen species and activated mitochondria-mediated pathways, including decreased MMP, activation of caspase3/caspase9, decreased Na⁺/K⁺-ATPase and Ca²⁺-ATPase activities, and disruption of the antioxidant system, resulting in the disruption of intracellular reduction-oxidation homeostasis. Monacolin K also activated MAPK and NF-κB pathways, upregulating P38 activity and downregulating JNK/ERK/P65/IκBα expression, ultimately leading to apoptosis of U251 cells. Importantly, monacolin K was not cytotoxic to normal human cells, hUC-MSCs. We concluded that monacolin K can induce apoptosis in U251 cells by triggering ROS-mediated oxidative damage and regulating MAPKs and NF-κB pathways.