Biology subjects

Harhaj, E. W.

Publications and source records attributed to Harhaj, E. W..

5 recordsLinked to original sources

bioRxiv2025

The aryl hydrocarbon receptor interacting protein suppresses RNA virus-induced type I IFN and IL-6 in mouse macrophages

Aryl hydrocarbon receptor (AhR) interacting protein (AIP) suppresses type I IFN production by interacting with and preventing the nuclear translocation of the transcription factor IRF7. The kinase TBK1 phosphorylates AIP to promote IRF7 binding and the inhibition of the type I interferon (IFN) response. However, it is unknown if AIP expression in innate immune cells is important to suppress type I IFN in the context of RNA virus infection in vitro and in vivo. In this study we generated myeloid cell-specific AIP conditional knockout mice (Aipfl/flxLysM-Cre) to investigate AIP regulation of innate immune signaling in myeloid cells. Bone marrow-derived macrophages (BMDMs) from Aipfl/flxLysM-Cre mice had diminished viral replication and increased production of IFN/b and IL-6 in response to RNA virus infection. AIP-deficient macrophages exhibited increased IRF7 expression and impaired virus-induced IRF7 degradation. AIP interacted with the E3 ubiquitin ligase SOCS1 and enhanced SOCS1 stability and its interaction with IRF7 to promote the proteasomal degradation of IRF7. Aipfl/flxLysM-Cre mice exhibited improved survival upon influenza A virus (IAV) infection compared to control mice. Together, these results indicate that myeloid cell-specific AIP suppresses the innate immune response by targeting IRF7.

immunology↗

bioRxiv2025

HTLV-1 Tax induces PINK1-Parkin-dependent mitophagy to mitigate activation of the cGAS-STING pathway

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATLL) and the neuroinflammatory disease, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLV-1 Tax regulatory protein plays a critical role in HTLV-1 persistence and pathogenesis; however, the underlying mechanisms are poorly understood. Here we show that Tax dynamically regulates mitochondrial reactive oxygen species (ROS) and membrane potential to trigger mitochondrial dysfunction. Tax is recruited to damaged mitochondria through its interaction with the IKK regulatory subunit NEMO and directly engages the ubiquitin-dependent PINK1-Parkin pathway to induce mitophagy. Tax also recruits autophagy receptors NDP52 and p62/SQSTM1 to damaged mitochondria to induce mitophagy. Furthermore, Tax requires Parkin to limit the extent of cGAS-STING1 activation and suppress type I interferon (IFN) induction. HTLV-1-transformed T cell lines and PBMCs from HAM/TSP patients exhibit hallmarks of chronic mitophagy, and inhibition of Parkin in HTLV-1-transformed cell lines downregulates p19 Gag expression and induces cell death. Collectively, our findings suggest that Tax manipulation of the PINK1-Parkin mitophagy pathway represents a new HTLV-1 immune evasion strategy important for maintaining viral gene expression and cell survival.

microbiology↗

bioRxiv2024

ZFAND6 is a subunit of a TRAF2-cIAP E3 ubiquitin ligase complex essential for mitophagy

The A20 ubiquitin-editing enzyme is a critical negative regulator of NF-{kappa}B signaling and inflammation. While the mechanisms by which A20 restricts inflammation have been extensively studied, the physiological functions of other A20-like proteins are largely unknown. Here, we report a previously unknown function of the A20 family member ZFAND6 as a novel regulator of mitophagy. Deletion of ZFAND6 in bone marrow-derived macrophages (BMDMs) promotes the upregulation of reactive oxygen species (ROS) and the accumulation of damaged mitochondria due to impaired mitophagy. Consequently, mitochondrial DNA (mtDNA) is released into the cytoplasm, triggering the spontaneous expression of interferon-stimulated genes (ISGs) in a cGAS-STING dependent manner, which leads to enhanced viral resistance in vitro. However, mice lacking ZFAND6 exhibit increased morbidity and mortality upon challenge with a sublethal dose of influenza A virus (IAV) due to impaired myeloid cell activation and diminished type I IFN signaling. Mechanistically, ZFAND6 bridges a TRAF2-cIAP1 interaction, which is required for the initiation of ubiquitin-dependent mitophagy. Our results suggest that ZFAND6 is a subunit of a TRAF2-cIAP E3 ligase complex that promotes the clearance of damaged mitochondria by mitophagy to maintain mitochondrial homeostasis.

immunology↗

bioRxiv2021

Phosphorylation of the selective autophagy receptor TAX1BP1 by canonical and noncanonical IκB kinases promotes its lysosomal localization and clearance of MAVS aggregates

TAX1BP1 is a selective autophagy receptor which inhibits NF-{kappa}B and RIG-I-like receptor (RLR) signaling to prevent excessive inflammation and maintain homeostasis. Selective autophagy receptors such as p62/SQSTM1 and OPTN are phosphorylated by the noncanonical I{kappa}B kinase TBK1 to stimulate their selective autophagy function. However, it is unknown if TAX1BP1 is regulated by TBK1 or other kinases under basal conditions or during RNA virus infection. Here, we found that the noncanonical I{kappa}B kinases TBK1 and IKKi phosphorylate TAX1BP1 to regulate its basal turnover, whereas the canonical I{kappa}B kinase IKK and the core autophagy factor ATG9 play essential roles in RNA virus-mediated TAX1BP1 autophagosomal degradation. TAX1BP1 phosphorylation by canonical and noncanonical I{kappa}B kinases promotes its localization to lysosomes resulting in its degradation. Furthermore, TAX1BP1 plays a critical role in the clearance of MAVS aggregates, and phosphorylation of TAX1BP1 augments its MAVS aggrephagy function. Together, our data support a model whereby I{kappa}B kinases license TAX1BP1 selective autophagy function to inhibit MAVS and RLR signaling. Author SummaryThe RIG-I-like receptor (RLR) pathway induces type I interferon (IFN) and proinflammatory cytokines in response to RNA virus infection. MAVS is a mitochondrial adaptor protein in the RLR pathway that forms prion-like aggregates upon activation; however, how MAVS aggregates are cleared to restore homeostasis is unclear. Autophagy is a lysosomal degradation pathway important for the clearance of potentially cytotoxic protein aggregates that could induce inflammation and/or cell death. TAX1BP1 is a selective autophagy receptor that inhibits RLR signaling, but the precise mechanisms remain unknown. Here, we found that TAX1BP1 is a substrate for multi-site phosphorylation by canonical and noncanonical I{kappa}B kinases which triggered its lysosomal localization and degradation. We also found that TAX1BP1 was critical for the clearance of MAVS aggregates in a phosphorylation-dependent manner. Overall, our data suggest that phosphorylation serves a key regulatory function for TAX1BP1 to inhibit RLR signaling.

immunology↗

bioRxiv2020

The E3/E4 ubiquitin conjugation factor UBE4B interacts with and ubiquitinates the HTLV-1 Tax oncoprotein to promote NF-kB activation

Human T-cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATLL), and the neurological disease HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLV-1 Tax protein persistently activates the NF-{kappa}B pathway to enhance the proliferation and survival of HTLV-1 infected T cells. Lysine 63 (K63)-linked polyubiquitination of Tax provides an important regulatory mechanism that promotes Tax-mediated interaction with the IKK complex and activation of NF-{kappa}B; however, the host proteins regulating Tax ubiquitination are largely unknown. To identify novel Tax interacting proteins that may regulate its ubiquitination we conducted a yeast two-hybrid screen using Tax as bait. This screen yielded the E3/E4 ubiquitin conjugation factor UBE4B as a novel binding partner for Tax. Here, we confirmed the interaction between Tax and UBE4B in mammalian cells by co-immunoprecipitation assays and demonstrated colocalization by proximity ligation assay and confocal microscopy. Overexpression of UBE4B specifically enhanced Tax-induced NF-{kappa}B activation, whereas knockdown of UBE4B impaired Tax-induced NF-{kappa}B activation and the induction of NF-{kappa}B target genes in T cells and ATLL cell lines. Furthermore, depletion of UBE4B with shRNA resulted in apoptotic cell death and diminished the proliferation of ATLL cell lines. Finally, overexpression of UBE4B enhanced Tax polyubiquitination, and knockdown or CRISPR/Cas9-mediated knockout of UBE4B attenuated both K48- and K63-linked polyubiquitination of Tax. Collectively, these results implicate UBE4B in HTLV-1 Tax polyubiquitination and downstream NF-{kappa}B activation. Author SummaryInfection with the retrovirus HTLV-1 leads to the development of either CD4+CD25+ leukemia/lymphoma (ATLL) or a demyelinating neuroinflammatory disease (HAM/TSP) in a subset of infected individuals. The HTLV-1 Tax protein is a regulatory protein which regulates viral gene expression and persistently activates cellular signaling pathways such as NF-{kappa}B to drive the clonal expansion and longevity of HTLV-1 infected CD4+ T cells. Polyubiquitination of Tax is a key mechanism of NF-{kappa}B activation by assembling and activating I{kappa}B kinase (IKK) signaling complexes; however, the host factors regulating Tax ubiquitination have remained elusive. Here, we have identified the E3/E4 ubiquitin conjugation factor UBE4B as a novel Tax binding protein that promotes both K48- and K63-linked polyubiquitination of Tax. Knockdown or knockout of UBE4B impairs Tax-induced NF-{kappa}B activation and triggers apoptosis of HTLV-1 transformed cells. Therefore, UBE4B is an integral host factor that supports HTLV-1 Tax polyubiquitination, NF-{kappa}B activation and cell survival.

microbiology↗