Biology subjects

Rijal, A.

Publications and source records attributed to Rijal, A..

3 recordsLinked to original sources

bioRxiv2026

HSF1 inhibition potentiates the antifungal activity and proteome instability induced by the fungal Hsp110 inhibitor 2H

Fungal infections remain a major cause of morbidity and mortality worldwide; however, therapeutic options are limited and are increasingly compromised by antifungal resistance. Heat Shock Protein 110 kDa (Hsp110) is an essential molecular chaperone required for protein homeostasis (proteostasis) and fungal viability and has recently emerged as a promising antifungal target. We previously identified 2H, a first-in-class inhibitor of fungal Hsp110 proteins that exhibits broad-spectrum antifungal activity through disruption of proteostasis. Heat Shock Transcription Factor 1 (HSF1), the master regulator of cellular stress responses and chaperone expression, has also been proposed as a potential antifungal target, although direct pharmacological evidence supporting this strategy remains limited. Here, we investigated the effects of combining the HSF1 inhibitor DTHIB with the fungal Hsp110 inhibitor 2H in Cryptococcus neoformans and Candida albicans. Although DTHIB alone exhibited minimal antifungal activity, it significantly enhanced the growth-inhibitory and fungicidal effects of 2H. Notably, this potentiating effect was specific to 2H and was not observed with fluconazole. Consistent with the roles of Hsp110 and HSF1 in proteostasis, 2H induced extensive accumulation of detergent-insoluble protein aggregates in C. neoformans, whereas HSF1 inhibition further increased both the abundance and diversity of aggregated proteins. Quantitative proteomic analyses demonstrated that 2H induces proteome-wide protein aggregation, impacting proteins involved in a broad range of essential cellular processes, with high-molecular-weight proteins exhibiting particular susceptibility. Together, these findings provide pharmacological evidence supporting HSF1 as a promising antifungal sensitization target and demonstrate the utility of 2H as a chemical probe for studying Hsp110-dependent proteostasis. Simultaneous disruption of both HSF1-mediated stress responses and Hsp110-dependent proteostasis promotes extensive proteome instability and enhances antifungal activity, highlighting a potential new strategy for antifungal drug development.

microbiology↗

bioRxiv2025

Differentiation-Dependent Proximity Proteomics Identifies Novel Host Factors Linked to HPV16 E2 Function

Human papillomavirus 16 (HPV16) is a causative agent of oropharyngeal, cervical and anogenital cancers. The viral E2 protein is essential for viral genome replication, transcriptional regulation, episome maintenance, and activation of the host DNA damage response. Despite its central role, the full network of HPV16 E2 interactions with host proteins remains incompletely defined, particularly under differentiating conditions which support the complete viral life cycle. In this study, we used TurboID-based proximity labeling to characterize the interactome of HPV16 E2 and known host partner protein TOPBP1, in both undifferentiated monolayer and differentiating keratinocytes. We generated stable keratinocyte lines expressing doxycycline-inducible TurboID-tagged HPV16 E2 and confirmed that the tagged protein retained transcriptional, replicative, and DNA damage-inducing functions. Mass spectrometry analysis of streptavidin-enriched proteins identified both known and novel E2-associated host factors, including chromatin regulators, DNA repair proteins, and nucleolar components. Comparative analysis revealed a substantial overlap between E2 and TOPBP1 interactomes, and in situ validation by proximity ligation assay identified nucleolin (NCL) as a differentiation-dependent factor whose interaction with E2 is stabilized by TOPBP1. Functional studies demonstrated that NCL is required for episomal genome maintenance, highlighting a cooperative E2-TOPBP1- NCL axis critical for viral genome stability during differentiation. These findings provide a comprehensive view of the E2-associated protein landscape in stratified epithelial cells and reveal a mechanistic pathway through which HPV16 co-opts host factors to support genome maintenance, productive replication, and persistence. ImportanceHuman papillomaviruses (HPVs) establish persistent infections in stratified epithelia and rely on host DNA damage and repair factors to support their replication. The E2 protein is central to viral genome replication and maintenance, and depends heavily on its interaction with the host factor TOPBP1 for these functions. Here, we define the E2 and TOPBP1 interactomes in differentiating keratinocytes, and identify nucleolin (NCL) a critical differentiation- and TOPBP1-dependent E2 partner required for episomal genome stability. These findings expand the understanding of how HPV16 coordinates viral replication with host chromatin and DNA repair networks, uncovering a cooperative E2-TOPBP1-NCL axis that may represent a new target for antiviral intervention.

cancer biology↗

bioRxiv2024

Role of histone variants H2BC1 and H2AZ.2 in H2AK119ub nucleosome organization and Polycomb gene silencing

Ubiquitination of histone H2A at lysine 119 residue (H2AK119ub) plays critical roles in a wide range of physiological processes, including Polycomb gene silencing 1,2, replication 3-5, DNA damage repair 6-10, X inactivation 11,12, and heterochromatin organization 13,14. However, the underlying mechanism and structural basis of H2AK119ub remains largely elusive. In this study, we report that H2AK119ub nucleosomes have a unique composition, containing histone variants H2BC1 and H2AZ.2, and importantly, this composition is required for H2AK119ub and Polycomb gene silencing. Using the UAB domain of RSF1, we purified H2AK119ub nucleosomes to a sufficient amount and purity. Mass spectrometry analyses revealed that H2AK119ub nucleosomes contain the histone variants H2BC1 and H2AZ.2. A cryo-EM study resolved the structure of native H2AK119ub nucleosomes to a 2.6A resolution, confirming H2BC1 in one subgroup of H2AK119ub nucleosomes. Tandem GST-UAB pulldown, Flag-H2AZ.2, and HA-H2BC1 immunoprecipitation revealed that H2AK119ub nucleosomes could be separated into distinct subgroups, suggesting their composition heterogeneity and potential dynamic organization. Knockout or knockdown of H2BC1 or H2AZ.2 reduced cellular H2AK119ub levels, establishing H2BC1 and H2AZ.2 as critical determinants of H2AK119ub. Furthermore, genomic binding profiles of H2BC1 and H2AZ.2 overlapped significantly with H2AK119ub binding, with the most significant overlapping in the gene body and intergenic regions. Finally, assays in developing embryos reveal an interaction of H2AZ.2, H2BC1, and RING1A in vivo. Thus, this study revealed, for the first time, that the H2AK119ub nucleosome has a unique composition, and this composition is required for H2AK119ub and Polycomb gene silencing.

molecular biology↗