Molecular characterization of the glucose-regulated protein 78 (GRP78) gene in planarian Dugesia japonica

Planarians (Platyhelminthes)-An Emerging Model Organism for Investigating Innate Immune Mechanisms

An organism responds to the invading pathogens such as bacteria, viruses, protozoans, and fungi by engaging innate and adaptive immune system, which functions by activating various signal transduction pathways. As invertebrate organisms (such as sponges, worms, cnidarians, molluscs, crustaceans, insects, and echinoderms) are devoid of an adaptive immune system, and their defense mechanisms solely rely on innate immune system components. Investigating the immune response in such organisms helps to elucidate the immune mechanisms that vertebrates have inherited or evolved from invertebrates. Planarians are non-parasitic invertebrates from the phylum Platyhelminthes and are being investigated for several decades for understanding the whole-body regeneration process. However, recent findings have emerged planarians as a useful model for studying innate immunity as they are resistant to a broad spectrum of bacteria. This review intends to highlight the research findings on various antimicrobial resistance genes, signaling pathways involved in innate immune recognition, immune-related memory and immune cells in planarian flatworms.

Evaluation of immunological response in shrimp Penaeus vannamei submitted to low temperature and air exposure

The objective of this study is to explore the immune response of the shrimp Penaeus vannamei to low temperature and air exposure during the mimic waterless transportation. Shrimp were cold shocked at 13 °C for 3 min, then exposed to air at 15 °C for 12 h, and finally revived in water at 25 °C. Hemocyte structure remained intact with only slight distortions of some organelles and nuclear membrane under the stress. Phenoloxidase (PO), lysozyme (Lys) and gamma-glutamyl transferase (GGT) activities, glutamine (Gln) content and relative mRNA expressions of prophenoloxidase (proPO), β-1,3-glucan binding protein (LGBP), ferrin (Fer) and glucose regulated protein 78 (GRP 78) increased and reached peak levels after 3 h-9 h of air exposure, and then decreased to relatively stable levels in the prolonged period of air exposure. The total hemocyte count (THC) and gene expressions of proPO, Fer and LGBP at the end of waterless storage were significantly lower (p < 0.05) than those in fresh shrimp while no significant difference (p ≥ 0.05) was found between revived and fresh shrimp in PO, Lys, GGT activities, Gln content and gene expression level of GRP 78. Of all the hemocytes, the percentage of semi granular cells (SGC) and granular cells (GC) significantly decreased after 6-9 h of storage, while hyaline cells (HC) dramatically increased after 9 h of storage to compensate the loss of SGC and GC. Results suggested that the low temperature and air exposure caused significant immunological response to the shrimp, but the damages to the immune system were partly reparable.

Molecular cloning, characterization, expression and enzyme activity of catalase from planarian Dugesia japonica in response to environmental pollutants

Catalase (CAT) is an important antioxidant enzyme that protects aerobic organisms against oxidative damage by degrading hydrogen peroxide to oxygen and water. CAT mRNAs have been cloned from many species and employed as useful biomarkers of oxidative stress. In the present study, we cloned the cDNA sequence of CAT gene from freshwater planarian Dugesia japonica (designated as DjCAT) by means of RACE method. Sequence analysis and multiple alignment jointly showed that the full-length cDNA sequence consists of 1734 nucleotides, encoding 506 amino acids. Three catalytic amino acid residues of His71, Asn144 and Tyr354, two CAT family signature sequences of a proximal active site signature (60FDRERIPERVVHAKGGGA77) and a heme-ligand signature motif (350RLFSYRDTQ358) are highly conserved, suggesting that the DjCAT belongs to the NADPH and heme-binding CAT family and has similar functions. In addition, the transcriptional level of CAT gene and activity of CAT enzyme upon acute exposure of environmental pollutants glyphosate and 1-decyl-3-methylimidazolium bromide ([C10mim]Br) were investigated systematically. The variation of CAT mRNA expression in D. japonica was quantified by real-time PCR and the results indicated that it was up-regulated after exposure to glyphosate or [C10mim]Br with a dose-dependent manner but not linearly. Even though the variation trend of CAT activity upon glyphosate stress was not monotonously increased and inconsistent with that after [C10mim]Br exposure on day 1 and 3 sampling time, with the duration prolonged to day 5 they both presented a dose-dependent increase and the differences achieved extreme significance in all treated groups compared to the control. These findings suggested that DjCAT plays an important role in antioxidant defense in D. japonica, and the mRNA expression of CAT would also be used as an effective biomarker to monitor the pollution in aquatic environment just like its corresponding enzyme.

The GRP94 gene of Yesso scallop (Patinopecten yessoensis): Characterization and expression regulation in response to thermal and bacterial stresses

The 94-kDa glucose-regulated protein (GRP94) belonging to the HSP90 family is an endoplasmic reticulum (ER) chaperone. It plays critical roles in ER quality control, and has been implicated as a specialized immune chaperone to regulate both innate and adaptive immunity. In this study, we identified and characterized a GRP94 gene (PyGRP94) from Yesso scallop (Patinopecten yessoensis). The protein sequence of PyGRP94 is highly conserved with its homologs in vertebrates, with a signal sequence in N-terminal, an ER retrieval signal sequence in C-terminal and a HATPase_c domain. Expression analysis suggests that PyGRP94 transcripts in early embryos are maternally derived and the zygotic expression is started from D-shaped larvae. This gene is also expressed in almost all the adult tissues examined except smooth muscle, with the highest expression level in hemocytes. Besides, PyGRP94 was demonstrated to be induced by heat shock and both Gram-positive (Micrococcus luteus) and Gram-negative (Vibrio anguillarum) bacterial infection, with much more dramatic changes being observed after V. anguillarum challenge. Our results suggest the involvement of PyGRP94 in response to thermal stress, and that it might play an important role in the innate immune defense of scallop.

Paclitaxel inhibits selenoprotein S expression and attenuates endoplasmic reticulum stress

The primary effect of the endoplasmic reticulum (ER) stress response or unfolded protein response (UPR) is to reduce the load of unfolded protein and promote survival. However, prolonged and severe ER stress leads to tissue injury and serious diseases. Thus, it is important to identify drugs that can attenuate ER stress for the treatment of diseases. Natural products continue to provide lead compounds for drug discovery and front-line pharmacotherapy for people worldwide. Previous studies have indicated that selenoprotein S (SelS) is a sensitive and ideal maker of ER stress. In the present study, a firefly luciferase reporter driven by the SelS gene promoter was used to screen for natural compounds capable of attenuating ER stress. From this, paclitaxel (PTX) was identified to efficiently inhibit the promoter activity of the SelS gene, and further results revealed that PTX significantly inhibited the tunicamycin-induced upregulation of SelS at the mRNA and protein levels in HepG2 and HEK293T cells. In addition, PTX was able to efficiently inhibit the expression of the ER stress marker, glucose-regulated protein 78, in ER stress, indicating that PTX may reverse ER stress. Taken together, these results suggest that PTX is able to inhibit SelS expression during ER stress and attenuate ER stress.

Molecular characterization of two novel molecular chaperones in bacterial-challenged Apostichopus japonicus

Molecular chaperones of 78 kDa glucose-regulated protein (GRP78) and protein disulfide isomerase (PDI) are involved in protein folding and assembly in the endoplasmic reticulum (ER). Increasing evidences also suggest that these two molecules play an important role in immune response. In the present study, we cloned and characterized GRP78 and PDI genes from Apostichopus japonicus by RNA-seq and RACE approaches (designated as AjGRP78 and AjPDI, respectively). The AjGRP78 cDNA was of 2355bp including an open reading frame (ORF) of 2013 bp encoding a protein of 670 amino acids with three heat shock protein 70 (HSP70) family signatures. AjGRP78 contained a 23-amino acid signal peptide at the N-terminus and a HDEL motif at the C-terminus, which supported the location of the protein in the ER. The full length cDNA of AjPDI was of 1893 bp with a 5' untranslated region (UTR) of 153 bp, a 3' UTR of 228 bp and an ORF of 1512 bp encoding a protein of 503 amino acids. A 17-amino acid signal peptide, two thioredoxin domains with two active sites of CGHC, and KDEL retention signal were totally conserved in the deduced amino acid of AjPDI. Phylogenic analysis and multiple alignments have shown that both genes shared remarkably higher degree of structural conservation and sequence identities with other counterparts from invertebrates and vertebrates, further supporting that the two proteins were novel members of molecular chaperone family. Spatial expression analysis revealed that AjGRP78 mRNA transcripts were dominantly expressed in the tentacle, while AjPDI mRNA levels were abundant in the muscle, intestine and respiratory trees. For Vibrio splendidus challenged sea cucumber, the peak expression of AjGRP78 and AjPDI mRNAs in coelomocytes were detected at 24h with 1.73-fold increase and at 6h with 1.83-fold increase compared with the control group, respectively. Similarly, a significant increase in the relative mRNA levels of AjGRP78 and AjPDI was also identified in 1 μg mL(-1) LPS exposed primary cultured coelomocytes. These results collectively suggested that AjGRP78 and AjPDI were ER chaperones of A. japonicus, of which expression is induced upon bacterial infection.