Biology subjects

Kalamvoki, M.

Publications and source records attributed to Kalamvoki, M..

6 recordsLinked to original sources

bioRxiv2026

Modulation of gp130 Cytokine Receptor Family by Herpes Simplex Virus 1 as a Strategy for Immune Evasion?

HSV-1 is a neurotropic human pathogen that establishes lifelong latency in sensory neurons. Periodic reactivation causes mucocutaneous lesions and, in some cases, severe corneal and neurological disease. While HSV-1 utilizes numerous viral proteins to extensively reprogram host signaling pathways and evade antiviral responses, how it alters host cytokine receptor networks remains poorly understood. Here, we demonstrate that HSV-1 infection selectively downmodulates multiple members of the gp130 (glycoprotein 130) cytokine receptor family, including gp130, Oncostatin M receptor {beta} (OSMR-{beta}), and leukemia inhibitory factor receptor (LIFR), while sparing IL-6Ra and CNTFRa (Ciliary Neurotrophic Factor Receptor). Because gp130 is the central signaling component of the IL-6 cytokine family and mediates JAK/STAT3 activation, its elimination likely represents a viral strategy to suppress inflammatory and antiviral signaling. Consistent with this, HSV-1 does not induce IL-6 mRNA expression in productively infected cells, suggesting coordinated inhibition of both cytokine production and receptor availability. Mechanistically, we found that the viral RNase VHS is at least partially responsible for gp130 family receptor downmodulation, likely in combination with virus-induced endocytosis/degradation pathways. Functionally, activation of gp130 signaling significantly impairs HSV-1 infection, demonstrating that suppression of antiviral cytokine responses is critical for virus replication. Finally, we determined that CNTF causes reactivation of latent HSV-1 using the LUHMES in vitro latency model, illustrating CNTFRa signaling contribution to latency and reactivation. A similar effect has been reported for IL-6. Together, these findings reveal a previously unrecognized immune evasion mechanism by which HSV-1 remodels gp130 cytokine signaling to promote infection.

microbiology↗

bioRxiv2026

Effect of HSV-1 ICP0 E3 ubiquitin ligase on CIN85 endosomes

Herpes simplex virus-1 (HSV-1) has infected more than 67% of the world population causing diseases that range in severity from benign cold sores to encephalitis. To infect and persist in the host, HSV-1 has evolved sophisticated strategies to counteract antiviral responses. The viral immediate early protein ICP0 (Infected Cells Protein 0) plays a fundamental role in this process. ICP0 is an E3 ubiquitin ligase that is required for successful onset of lytic infection and productive reactivation of viral genomes from latency. Most ICP0 studies have been focused on its nuclear functions, but late gene expression drives accumulation of ICP0 to the cytoplasm where its functions are unknown. We recently demonstrated that cytoplasmic ICP0 localizes on the surface of endosomes through its interaction with CIN85 (Cbl-interacting protein of 85 kDa), a scaffolding protein for factors involved in endocytosis. This interaction is required for extrusion of host antiviral factors and immunoevasion. Here, we report that the E3 ubiquitin ligase activity of ICP0 is also required for these effects, as disruption of ICP0 RING finger domain, which disrupts its catalytic activity, resulted in an increase in the number of CIN85 endosomes that cannot be exocytosed. These endosomes colocalize with autophagosome components, but they do not enter the lysosomal pathway for degradation. Mutant viruses that cannot exocytose CIN85 endosomes produce EVs that are more potent at activating antiviral responses.

microbiology↗

bioRxiv2026

Herpes simplex virus 1 subverts the mitochondrial network to support the infection: A lesson on mitochondrial versatility

Herpes simplex virus 1 (HSV-1) infects approximately 67% of the population worldwide. It establishes lifelong reservoirs in sensory neurons and has been linked to several diseases including neuronal dysfunction. Disruption of mitochondrial homeostasis is a hallmark of HSV-1 infection, however a molecular understanding of these changes and their significance is not yet well defined. HSV-1 infection causes a UL12.5-dependent inhibition of mitochondrial biogenesis through the loss of mitochondrial DNA and mitochondrial transcription factors, PGC-1 (peroxisome proliferator-activated receptor-gamma co-activator) and TFAM (mitochondrial transcription factor). Conversely, UL12.5-independent mechanisms inhibit mitochondrial fusion by activating the OMA1 metallopeptidase that cleaves the inner mitochondrial membrane fusion protein OPA1 (optic atrophy protein 1) and by down-modulating the outer mitochondrial membrane fusion protein MFN2 (mitofusin 2). This inhibition of fusion results in a smaller mitochondrial network that clusters to perinuclear regions, likely supplying energy for viral replication and envelopment. The inner mitochondrial membrane protein TIM23 is also down-modulated during infection in a UL12.5-independent mechanism. Failure of the virus to promote these changes negatively impacts the infection. Despite these changes, mitochondria are protected from mitophagy due to the viral-induced degradation of several mitophagy adaptor proteins, whereby damaged mitochondrial components, including mitochondrial DNA, are extruded via extracellular vesicles. These mitochondrial changes still support functions necessary for HSV-1 infection. Basal cell respiration is preserved, while spare respiratory capacity and extracellular acidification rates increase, indicating glycolytic activity. Mitochondrial membrane potential is also preserved. Overall, our studies provide mechanistic insight into how HSV-1 impacts mitochondria, which could contribute to viral pathogenesis.

microbiology↗

bioRxiv2023

The Role of the Tyrosine-Based Sorting Signals of the ORF3a Protein of SARS-CoV-2 on Intracellular Trafficking, Autophagy, and Apoptosis

The open reading frame 3a (ORF3a) is an accessory transmembrane protein that is important to the pathogenicity of SARS-CoV-2. The cytoplasmic domain of ORF3a has three canonical tyrosine-based sorting signals (Yxx{Phi}; where x is any amino acid and {Phi} is a hydrophobic amino acid with a bulky -R group). They have been implicated in the trafficking of membrane proteins to the cell plasma membrane and to intracellular organelles. Previous studies have indicated that mutation of the 160YSNV163 motif abrogated plasma membrane expression and inhibited ORF3a-induced apoptosis. However, two additional canonical tyrosine-based sorting motifs (211YYQL213, 233YNKI236) exist in the cytoplasmic domain of ORF3a that have not been assessed. We removed all three potential tyrosine-based motifs and systematically restored them to assess the importance of each motif or combination of motifs that restored efficient trafficking to the cell surface and lysosomes. Our results indicate that the Yxx{Phi} motif at position 160 was insufficient for the trafficking of ORF3a to the cell surface. Our studies also showed that ORF3a proteins with an intact Yxx{Phi} at position 211 or at 160 and 211 were most important. We found that ORF3a cell surface expression correlated with the co-localization of ORF3a with LAMP-1 near the cell surface. These results suggest that Yxx{Phi} motifs within the cytoplasmic domain may act cooperatively in ORF3a transport to the plasma membrane and endocytosis to lysosomes. Further, our results indicate that certain tyrosine mutants failed to activate caspase 3 and did not correlate with autophagy functions associated with this protein. IMPORTANCEOpen reading frame 3a (ORF3a) encodes for the largest of the SARS-CoV-2 accessory proteins. While deletion of the ORF3a gene from SARS-CoV-2 results in a virus that replicates slightly less efficiently in cell culture, deletion also results in a virus that is less pathogenic in mouse models of SARS-CoV-2 infections. The ORF3a has been reported to be a viroporin, induces apoptosis and incomplete autophagy in cells. Thus, determining the domains involved in these functions will further our understanding of how this protein influences virus assembly and pathogenesis. Here, we investigated the role of the three potential tyrosine-based sorting signals in the cytoplasmic domain of the ORF3a on intracellular protein trafficking, apoptosis, and in the initiation of autophagy. Our results indicate that more than one Yxx{Phi} motif is required for efficient transport of ORF3a, ORF3a expression resulted in minimal apoptosis, and cell surface expression was not required for autophagy.

cell biology↗

bioRxiv2022

The Envelope Protein of SARS-CoV-2 Inhibits Viral Protein Synthesis and Infectivity of Human Immunodeficiency Virus type 1 (HIV-1)

The human coronavirus SARS-CoV-2 encodes for a small 75 amino acid transmembrane protein known as the envelope (E) protein. The E protein forms an ion channel, like the viroporins from human immunodeficiency virus type 1 (HIV-1) (Vpu) and influenza A virus (M2). Here, we analyzed HIV-1 virus infectivity in the presence of four different {beta}-coronavirus E proteins. We observed that the SARS-CoV-2 and SARS-CoV E proteins reduced HIV-1 yields by approximately 100-fold while MERS-CoV or HCoV-OC43 E proteins restricted HIV-1 infectivity to a lesser extent. This was also reflected in the levels of HIV-1 protein synthesis in cells. Mechanistically, we show that that the E protein neither affected reverse transcription nor genome integration. However, SARS-CoV-2 E protein activated the ER-stress pathway associated with the phosphorylation of eIF-2, which is known to attenuate protein synthesis in cells. Finally, we show that these four E proteins and the SARS-CoV-2 N protein did not significantly down-regulate bone marrow stromal cell antigen 2 (BST-2) while the spike (S) proteins of SARS-CoV and SARS-CoV-2, and HIV-1 Vpu efficiently down-regulated cell surface BST-2 expression. The results of this study show for the first time that viroporins from a heterologous virus can suppress HIV-1 infection. IMPORTANCEThe E protein of coronaviruses is a viroporin that is required for efficient release of infectious virus and for viral pathogenicity. We determined if the E protein from four {beta}-coronaviruses could restrict virus particle infectivity of HIV-1 infection. Our results indicate that the E proteins from SARS-CoV-2 and SARS-CoV potently restricted HIV-1 while those from MERS-CoV and HCoV-OC43 were less restrictive. Substitution of the highly conserved proline in the cytoplasmic domain of SARS-CoV-2 E abrogated the restriction on HIV-1 infection. Mechanistically, the SARS-CoV-2 E protein did not interfere with viral integration or RNA synthesis but rather reduced viral protein synthesis. We show that the E protein-initiated ER stress causing phosphorylation of eIF-2, which is known to attenuate protein synthesis. Companion studies suggest that the E protein also triggers autophagy. These results show for the first time that a viroporin from a coronavirus can restrict infection of another virus.

microbiology↗

bioRxiv2022

SARS-CoV-2 harnesses host translational shutoff and autophagy to optimize virus yields: The role of the envelope (E) protein

The SARS-CoV-2 virion is composed of four structural proteins: spike (S), nucleocapsid (N), membrane (M), and envelope (E). E spans the membrane a single time and is the smallest, yet most enigmatic of the structural proteins. E is conserved among coronaviruses and has an essential role in virus-mediated pathogenesis. We found that ectopic expression of E had deleterious effects on the host cell as it activated stress responses, leading to phosphorylation of the translation initiation factor eIF2 and LC3 lipidation that resulted in host translational shutoff. During infection E is highly expressed although only a small fraction is incorporated into virions, suggesting that E activity is regulated and harnessed by the virus to its benefit. In support of this, we found that the {gamma}1 34.5 protein of herpes simplex virus 1 (HSV-1) prevented deleterious effects of E on the host cell and allowed for E protein accumulation. This observation prompted us to investigate whether other SARS-CoV-2 structural proteins regulate E. We found that the N and M proteins enabled E protein accumulation, whereas S prevented E accumulation. While {gamma}1 34.5 protein prevented deleterious effects of E on the host cells, it had a negative effect on SARS-CoV-2 replication. This negative effect of {gamma}1 34.5 was most likely associated with failure of SARS-CoV-2 to divert the translational machinery and with deregulation of autophagy pathways. Overall, our data suggest that SARS-CoV-2 causes stress responses and subjugates these pathways, including host protein synthesis (phosphorylated eIF2) and autophagy, to support optimal virus production. ImportanceIn 2020, a new {beta}-coronavirus, SARS-CoV-2, entered the human population that has caused a pandemic resulting in 6 million deaths worldwide. Although closely related to SARS-CoV, the mechanisms of SARS-CoV-2 pathogenesis are not fully understood. We found that ectopic expression of the SARS-CoV-2 E protein had detrimental effects on the host cell, causing metabolic alterations including shutoff of protein synthesis and mobilization of cellular resources through autophagy activation. Co-expression of E with viral proteins known to subvert host antiviral responses such as autophagy and translational inhibition, either from SARS-CoV-2 or from heterologous viruses increased cell survival and E protein accumulation. However, such factors were found to negatively impact SARS-CoV-2 infection, as autophagy contributes to formation of viral membrane factories, and translational control offers an advantage for viral gene expression. Overall, SARS-CoV-2 has evolved mechanisms to harness host functions that are essential for virus replication.

microbiology↗