A molluscan extracellular signal-regulated kinase is involved in host response to immune challenges in vivo and in vitro. Issue 62 (March 2017) - Qu, Fufa
Abstract: Extracellular signal-regulated kinases (ERKs) are a group of highly conserved serine/threonine-specific protein kinases that function as important signaling intermediates in mitogen-activated protein kinase (MAPK) pathways, which are involved in a wide variety of cellular activities, including proliferation, inflammation and cytokine production. However, little is known about the roles of this kinase in mollusk immunity. In this study, we identified a molluscan ERK homolog ( Ch ERK) in the Hong Kong oyster ( Crassostrea hongkongensis ) and investigated its biological functions. The open reading frame (ORF) of Ch ERK encoded a polypeptide of 365 amino acids, with a predicted molecular weight of 41.96 kDa and pI of 6.43. The predicted Ch ERK protein contained typical characteristic motifs of the ERK family, including a dual threonine-glutamate-tyrosine (TEY) phosphorylation motif and an ATRW substrate binding site. Phylogenetic analysis revealed that Ch ERK belonged to the mollusk cluster and shared a close evolutionary relationship with ERK from Crassostrea gigas . In addition, quantitative real-time PCR analysis revealed that Ch ERK expression was detected in all of the examined tissues and stages of embryonic development; its transcript level was significantly induced upon challenge with bacterial pathogens ( Vibrio alginolyticus and Staphylococcus haemolyticus ) in vivo and PAMPs (lipopolysaccharide and peptidoglycan) in vitro . Moreover, Ch ERK was mainly located in the cytoplasm of HEK293T cells. Taken together, these findings may provide novel insights into the functions of molluscan ERKs, especially their roles in response to immune challenge in oyster. Highlights: A novel oyster ERK was first identified from Crassostrea hongkongensis. Ch ERK shared a significant homology with other mollusk ERK proteins. Ch ERK was constitutively expressed in all examined oyster tissues and developmental stages. Ch ERK expression was significantly induced in response to bacterial pathogens and PAMPs challenges. Ch ERK was found to be located mainly in the cytoplasm of HEK293T cells.