Identification and functional characterization of Histone‐like DNA‐binding protein in Nocardia seriolae (NsHLP) involved in cell apoptosis

Abstract

Nocardia seriolae, a facultative intracellular bacterium, is the main pathogen of fish nocardiosis. Bioinformatic analysis showed that the histone‐like DNA‐binding protein (HLP) gene of N. seriolae (nshlp) encoded a secreted protein and might target the mitochondria in the host cell. To further study the preliminary function of HLP in N. seriolae (NsHLP), the gene cloning, extracellular products identification, subcellular localization, overexpression and apoptosis detection assay were carried out in this study. Mass spectrometry analysis of the extracellular products from N. seriolae showed that NsHLP was a secreted protein. Subcellular localization of HLP‐GFP fusion proteins mainly assembled in the nucleus, which indicated that the NsHLP was co‐located with the nucleus rather than mitochondria in fathead minnow (FHM) cells. Notably, the expression of NsHLP had changed the distribution of mitochondria into lumps in the FHM cell. In addition, apoptotic features were found in the transfected FHM cells by overexpression of NsHLP. Quantitative assays of mitochondrial membrane potential value, caspase‐3 activity and pro‐apoptotic genes mRNA (Bad, Bid and Bax) expression level demonstrated that the cell apoptosis was induced in the transfected FHM cells. All the results presented in this study provided insight on the function of NsHLP, which suggested that it may participate in the cell apoptosis regulation and play an important role in the pathogenesis of N. seriolae.

Isolation and characterization of Nocardia seriolae , a causative agent of systematic granuloma in cultured East Asian four finger threadfin, Eleutheronema rhadinum, and red snapper, Lutjanus erythropterus

“…This phenomenon also occurred on cultured eel, A. japonica (Kim et al., 2018). N. seriolae causes illness in fish and possesses several intracellular virulence factors (tyrosine phosphatase A, protein tyrosine phosphatase B, antigen 85 (Ag85), and TlyA protein) and produces an extracellular product (histone‐like DNA‐binding protein), which can cause immune depression, haemolysis and can induce disease in fish (Wang et al., 2019; Yasuike et al., 2017).…”

Characterization and function study of a glutamyl endopeptidase homolog from Nocardia seriolae

“…piscicida (Costa‐Ramos et al., 2011), and AIP56‐induced phagocyte apoptosis involves activation of caspase‐3 and mitochondria as shown by loss of ΔΨm. Previous study had reported that histone‐like DNA‐binding protein from N. seriolae was considered to be a virulence factor that induces cell apoptosis by degradation of mitochondrial membrane potential, activation of caspase‐3 and pro‐apoptosis genes (Wang et al., 2019). Based on the previous studies and the results obtained in this study, it is a reason to believe that GluNS is the potential virulence factor of N. seriolae .…”

“…Notably, N. seriolae has become the main pathogen of fish nocardiosis recently. The outbreak of fish nocardiosis induced by N. seriolae caused heavy economic losses in aquaculture(Chen et al., 2019; Wang et al., 2019). Moreover, the pathogenic virulence factors of N. seriolae are still unclear.…”

Identification of a cell‐wall peptidase (NlpC/P60) from Nocardia seriolae which induces apoptosis in fathead minnow cells

“…Nocardia seriolae is a Gram‐positive facultatively intracellular pathogen, which belongs to actinomycetes, Nocardia family and Nocardia genus in taxonomy, and can infect the fish with low immunity through gills or wound (Nayak, Shibasaki and Nakanishi, 2014; Wang et al, 2019). Notably, N. seriolae can evade intracellular killing after being engulfed by macrophages and disseminate in the host and cause widespread infection along with the migration of macrophages (Barry & Beaman, 2007; Ho et al, 2016).…”