The first molluscan TCTP in Venerupis philippinarum: Molecular cloning and expression analysis

Abstract

Translationally controlled tumor protein (TCTP) is one of the abundant and ubiquitously expressed proteins in metazoans. In the present study, the first molluscan TCTP (denoted as VpTCTP) was identified from Venerupis philippinarum haemocytes by EST and RACE approaches. The full-length cDNA of VpTCTP consisted of 1148 nucleotides with an open-reading frame of 555 bp encoding 184 amino acids. The deduced amino acid sequence of VpTCTP shared high similarity with TCTPs from other species, indicating that VpTCTP should be a new member of TCTP family. Several highly conserved motifs, including 5′terminal ologopyrimidine (5′TOP) starting sequence and rich AU and AUUT elements in 3′UTR, were also identified in VpTCTP. The tissue and temporal expression of VpTCTP after Vibrio anguillarum challenge was recorded by quantitative real-time RT-PCR. VpTCTP transcript could be detected in all examined tissues with the highest expression level in haemocytes and the lowest in hepatopancreas. Concerning the time-course expression in haemocytes, the relative expression of VpTCTP mRNA was down-regulated sharply from 6 h to 12 h post-infection. Then, the expression level was obviously up-regulated and reached 3.4-fold to that in the control group at 48 h post challenge. As time progressed, the expression of VpTCTP recovered to the original level at 96 h. All these results indicated that VpTCTP was an acute-phase protein involved in the immune response of V. philippinarum.

Introduction

The translationally controlled tumor protein, commonly known as TCTP, is a highly conserved protein existed in a range of eukaryotic organisms, including protozoa, yeasts, plants, nematodes and mammals. Recently, much attention has been paid to the ubiquitous protein for its multiple roles in various biologically and medically relevant processes [1]. Accumulating evidence indicates that TCTP could: 1) regulate cell growth, division, organ size and apoptosis [2], [3], [4]; 2) be involved in stress responses caused by heavy metals and heat shock [5], [6]; 3) be relevant in the defense against virus or bacterial pathogen [7], [8].

Solution structure analysis showed that yeast TCTP shared structural similarity to a family of guanine nucleotide-free chaperones, indicating that TCTP might be functioned as molecular chaperone [9]. Gnanasekar et al. also demonstrated that both human and parasite Schistosoma mansoni TCTPs could bind to a variety of denatured proteins and protect them from the harmful effects of thermal shock [10]. Moreover, the human TCTP mRNA was found to posses a strong secondary structure and able to induce the dsRNA-dependent protein kinase R, suggesting a connection to the interferon pathway [1]. In shrimp Penaeus japonicus and Penaeus monodon, TCTP expression was both up-regulated after WSSV challenge, while the level of P. monodon TCTP expression was significantly decreased when shrimp showed the mortality characteristic, indicating that TCTP was a key factor involved in innate immunity [11], [12].

As an important protein involved in host immunity response with chaperone activity, TCTP has not been identified from mollusk so far. In order to fill in the gap, the present study aims to: (1) clone the full-length cDNA of TCTP from Venerupis philippinarum (denoted as VpTCTP); (2) investigate the tissue and temporal expression profile of VpTCTP after being infected by Vibrio anguillarum pathogen.