Williford, Z. | Search bioRxiv

bioRxiv2026

Nucleus remodeling activity is conserved amongst diverse SIV Vpr isolates

Human immunodeficiency virus (HIV) encodes four accessory proteins that are essential for virus replication in vivo, primarily through the counteraction of host innate immune defense mechanisms. One of these proteins, Vpr, induces constitutive DNA damage repair (DDR) signaling to drive global epigenetic remodeling and activation of transcription programs that enhance HIV-1 promoter activity during acute infection and virus reactivation from latency. Vpr is conserved amongst diverse simian immunodeficiency virus (SIV) strains; however, the evolutionary breadth of Vpr's nucleus remodeling activity has yet to be thoroughly characterized. Here, we investigate a diverse panel of 16 SIV Vpr isolates and demonstrate that 13 out of 16 are capable of significantly activating DDR signaling compared to control infected cells. Moreover, cells infected with these isolates also exhibit increased abundance of two histone marks associated with transcription and euchromatin formation, as well as increased activation of two transcription factors known to be critical for HIV-1 promoter activity. Furthermore, site-directed mutagenesis of a highly homologous SIV Vpr isolate that failed to engage the DDR response revealed previously uncharacterized amino acid residues required for HIV-1 Vpr DDR engagement. Finally, structural modeling and functional analyses revealed that phylogenetically diverse Vpr isolates from SIV African green monkey strains induce nucleus remodeling through an evolutionarily distinct set of amino acid residues. Together, these findings demonstrate that hijacking of DDR responses to promote remodeling of the nuclear environment is a broadly conserved Vpr function.

microbiology↗

bioRxiv2025

Chlamydia trachomatis restricts signaling through NOD2 until late in the pathogen's developmental cycle

Pathogenic chlamydial species restrict their peptidoglycan (PG) to the division septum of their replicative forms. PG is a microbe-associated molecular pattern (MAMP) and two of its major pattern recognition receptors in human cells are nucleotide-binding oligomerization domain-containing proteins 1 and 2 (NOD1 and NOD2, respectively). It has been proposed that this unique morphological feature is evidence of pathoadaptation by the microbe, permitting PG-dependent cell division while also reducing the bacteriums recognition by innate immune receptors. Chlamydia trachomatis-infected cells activate NOD1 signaling within 8-12 hours of exposure to the bacterium, roughly coinciding with the microbes transition from its infectious to replicative forms. Here we report that, unlike NOD1 signaling, Chlamydia-induced NOD2 signaling does not occur until later in the pathogens developmental cycle. Both C. trachomatis and the related murine pathogen Chlamydia muridarum signal late in infection in HEK293 reporter cell lines expressing either human or murine-derived NOD2 receptors. NOD2 signaling can be modulated by disruption of the chlamydial amidase enzyme, AmiACT, interrupting the microbes developmental cycle, and treatment with inhibitors of lipooligosaccharide or peptidoglycan biosynthesis / assembly. These results mirror prior observations with Chlamydia-induced TLR9 signaling, leading us to hypothesize that Chlamydia-induced NOD2 signaling results from lytic events that occur sporadically during the transition between the pathogens developmental forms. Given our finding that pre-treating cells with NOD2-stimulatory ligands reduces chlamydial inclusion size and delays the developmental cycle, we hypothesize that the microbe preferentially degrades its PG during development to reduce the generation of NOD2 ligands.

microbiology↗