NAP1L1 Regulates Hepatitis C Virus Entry and Interacts with NS3

NAP1L1 is a novel microtubule-associated protein

Microtubule-associated proteins (MAPs) regulate assembly and stability of microtubules (MTs) during cell cytokinesis, cell migration, neuronal growth, axon guidance, and synapse formation. Using data mining of the Human Protein Atlas database and experimental screening, we identified nucleosome assembly protein 1 like 1 (NAP1L1) as a new MAP. The Human Protein Atlas and PubMed database screening identified 99 potential new MAPs. Twenty candidate proteins that highly co-localized with MTs were exogenously expressed with green fluorescent protein (GFP) or hemagglutinin (HA) tags in tissue culture cells and MTs were co-stained for immunofluorescent microscopy. We found that NAP1L1 is mainly localized in the cytosol with MTs during interphase. Using bacterially expressed recombinant NAP1L1 fragments and purified MTs, we biochemically mapped the MT-binding site on the N-terminal region (1-72aa) and the central region (164-269aa) of NAP1L1. NAP1L1 dimerizes through the long helix region (73-163aa), and full-length NAP1L1 induces the formation of thick MTs, indicating that NAP1L1 has the ability to bundle MTs in cells. Analysis of publicly available RNA-seq data of NAP1L1 depleted cells suggested that NAP1L1 is involved in cell adhesion and migration in agreement with the function of NAP1L1 as a MAP.

NAP1L1 promotes tumor proliferation through HDGF/C-JUN signaling in ovarian cancer

Background

Nucleosome assembly protein 1-like 1 (NAP1L1) is highly expressed in various types of cancer and plays an important role in carcinogenesis, but its specific role in tumor development and progression remains largely unknown. In this study, we suggest the potential of NAP1L1 as a prognostic biomarker and therapeutic target for the treatment of ovarian cancer (OC).

Methods

In our study, a tissue microarray (TMA) slide containing specimens from 149 patients with OC and 11 normal ovarian tissues underwent immunohistochemistry (IHC) to analyze the correlation between NAP1L1 expression and clinicopathological features. Loss-of- function experiments were performed by transfecting siRNA and following lentiviral gene transduction into SKOV3 and OVCAR3 cells. Cell proliferation and the cell cycle were assessed by the Cell Counting Kit-8, EDU assay, flow cytometry, colony formation assay, and Western blot analysis. In addition, co-immunoprecipitation (Co-IP) and immunofluorescence assays were performed to confirm the relationship between NAP1L1 and its potential targets in SKOV3/OVCAR3 cells.

Results

High expression of NAP1L1 was closely related to poor clinical outcomes in OC patients. After knocking down NAP1L1 by siRNA or shRNA, both SKOV3 and OVCAR3 cells showed inhibition of cell proliferation, blocking of the G1/S phase, and increased apoptosis in vitro. Mechanism analysis indicated that NAP1L1 interacted with hepatoma-derived growth factor (HDGF) and they were co-localized in the cytoplasm. Furthermore, HDGF can interact with jun proto-oncogene (C-JUN), an oncogenic transformation factor that induces the expression of cyclin D1 (CCND1). Overexpressed HDGF in NAP1L1 knockdown OC cells not only increased the expression of C-JUN and CCND1, but it also reversed the suppressive effects of si-NAP1L1 on cell proliferation.

Conclusions

Our data demonstrated that NAP1L1 could act as a prognostic biomarker in OC and can interact with HDGF to mediate the proliferation of OC, and this process of triggered proliferation may contribute to the activation of HDGF/C-JUN signaling in OC cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09356-z.

NAP1L5 Promotes Nucleolar Hypertrophy and Is Required for Translation Activation During Cardiomyocyte Hypertrophy

Pathological growth of cardiomyocytes during hypertrophy is characterized by excess protein synthesis; however, the regulatory mechanism remains largely unknown. Using a neonatal rat ventricular myocytes (NRVMs) model, here we find that the expression of nucleosome assembly protein 1 like 5 (Nap1l5) is upregulated in phenylephrine (PE)-induced hypertrophy. Knockdown of Nap1l5 expression by siRNA significantly blocks cell size enlargement and pathological gene induction after PE treatment. In contrast, Adenovirus-mediated Nap1l5 overexpression significantly aggravates the pro-hypertrophic effects of PE on NRVMs. RNA-seq analysis reveals that Nap1l5 knockdown reverses the pro-hypertrophic transcriptome reprogramming after PE treatment. Whereas, immune response is dominantly enriched in the upregulated genes, oxidative phosphorylation, cardiac muscle contraction and ribosome-related pathways are remarkably enriched in the down-regulated genes. Although Nap1l5-mediated gene regulation is correlated with PRC2 and PRC1, Nap1l5 does not directly alter the levels of global histone methylations at K4, K9, K27 or K36. However, puromycin incorporation assay shows that Nap1l5 is both necessary and sufficient to promote protein synthesis in cardiomyocyte hypertrophy. This is attributable to a direct regulation of nucleolus hypertrophy and subsequent ribosome assembly. Our findings demonstrate a previously unrecognized role of Nap1l5 in translation control during cardiac hypertrophy.

Hepatitis C Virus NS2 Protein Suppresses RNA Interference in Cells

RNAi interference (RNAi) is an evolutionarily conserved post-transcriptional gene silencing mechanism and has been well recognized as an important antiviral immunity in eukaryotes. Numerous viruses have been shown to encode viral suppressors of RNAi (VSRs) to antagonize antiviral RNAi. Hepatitis C virus (HCV) is a medically important human pathogen that causes acute and chronic hepatitis. In this study, we screened all the nonstructural proteins of HCV and found that HCV NS2 could suppress RNAi induced either by small hairpin RNAs (shRNAs) or small interfering RNAs (siRNAs) in mammalian cells. Moreover, we demonstrated that NS2 could suppress RNAi via its direct interaction with double-stranded RNAs (dsRNAs) and siRNAs, and further identified that the cysteine 184 of NS2 is required for the RNAi suppression activity through a serial of point mutation analyses. Together, our findings uncovered that HCV NS2 can act as a VSR in vitro, thereby providing novel insights into the life cycle and virus-host interactions of HCV.