The class A scavenger receptor member 3 (SCARA3) regulates cell apoptosis through X-linked apoptosis inhibitory protein (XIAP) in turbot (Scophthalmus maximus L.)

Abstract

Class A scavenger receptor 3 (SCARA3), a macrophage scavenger receptor-like protein, plays important roles in inhibiting cell proliferation, migration, and invasion. In the present study, a SCARA3 gene of turbot (SmSCARA3) (Gene ID: 118289953) with an 1815 bp ORF encoding 604 amino acids was identified. Phylogenetic analysis revealed that SmSCARA3 showed the closest relationship to that counterpart of olive flounder (Paralichthys olivaceus). The synteny analysis demonstrated conserved syntenic patterns across selected vertebrates. In addition, SmSCARA3 was ubiquitously expressed in all the examined tissues, with the highest expression level in intestine and the lowest expression level in the brain. SmSCARA3 exhibited different expression patterns in mucosal tissues (intestine, gill, skin) after two bacterial infections. Subsequently, recombinant SmSCARA3 protein (rSmSCARA3) revealed the strong binding affinity to LPS and responded primarily to LPS stimulation in intestinal cells of turbot. Additionally, the interference and overexpression experiments indicated that SmSCARA3 was associated with apoptosis related genes, such as Caspase1, Caspase3 and Caspase3a, and it could activate Caspase3 in HEPG2 cells. Moreover, flow cytometry revealed the apoptosis of SmSCARA3 overexpression group increased by 10.03%, which was consistent with the effect of SmSCARA3 on proliferation inhibition in intestinal cells of turbot. The cell apoptosis levels in the SmSCARA3-Flag and XIAP-HA experimental group were significantly lower than that in the control group (51.17% vs 72.72%). Finally, the Co-IP assay showed that SmSCARA3 could directly interact with XIAP. In conclusion, our results indicated that SmSCARA3 could activate Caspase3 and modulate apoptosis through XIAP , highlighting its potential roles as a therapeutic target for fish diseases.