Grass carp (Ctenopharyngodon idella) RSK2 protects cells anti-apoptosis by up-regulating BCL-2

Molecular characterization and expression analysis of B-cell lymphoma-2 in Trachinotus ovatus and its role in apoptotic process

Introduction

B-cell lymphoma-2 (Bcl-2) is the first identified member of the Bcl-2 family that performs an anti-apoptotic function in mammals. However, its role in teleosts is not fully understood. In this study, Bcl-2 of Trachinotus ovatus (TroBcl2) was cloned, and its role in apoptosis was investigated.

Methods

In this study, Bcl-2 of Trachinotus ovatus (TroBcl2) was cloned by PCR. Quantitative real-time PCR (qRT-PCR) was used to detect its mRNA expression level in healthy condition and after LPS stimulation. Subcellular localization was performed by transfecting the pTroBcl2-N3 plasmid into golden pompano snout (GPS) cells and observed under an inverted fluorescence microscope DMi8 and further verified by immunoblotting. In vivo overexpression and RNAi knockdown method were performed to evaluate the role of TroBcl2 in apoptosis. The anti-apoptotic activity of TroBcl2 was detected by flow cytometry. The effect of TroBcl2 on the mitochondrial membrane potential (MMP) was measured by an enhanced mitochondrial membrane potential assay kit with JC-1. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method was performed to evaluate the role of TroBcl2 in the DNA fragmentation. Immunoblotting was used to verify whether TroBcl2 inhibits the release of cytochrome c from mitochondria into the cytoplasm. The Caspase 3 and Caspase 9 Activity Assay Kits were used to investigate the effect of TroBcl2 on caspase 3 and caspase 9 activities. The effects of TroBcl2 on the expression of apoptosis-related and nuclear factor- κB (NF-κB) signaling pathway-related genes in vitro were evaluated by qRT-PCR and Enzyme linked immunosorbent assay (ELISA). Luciferase reporter assay was used to evaluate the activity in NF-κB signaling pathway.

Results and discussion

The full-length coding sequence of TroBcl2 contains 687 bp and encodes a protein containing 228 amino acids. Four conserved Bcl-2 homology (BH) domains and one invariant “NWGR” motif located in BH1 were identified in TroBcl2. In healthy T. ovatus, TroBcl2 was widely distributed in the eleven tested tissues, and higher expression levels were found in immune-related tissues, such as spleen and head kidney tissues. After stimulation with lipopolysaccharide (LPS), the expression of TroBcl2 in the head kidney, spleen, and liver was significantly upregulated. In addition, subcellular localization analysis revealed that TroBcl2 was localized in both the cytoplasm and nucleus. Functional experiments showed that TroBcl2 inhibited apoptosis, possibly by reducing mitochondrial membrane potential loss, decreasing DNA fragmentation, preventing cytochrome c release into cytoplasm, and reducing the caspase 3 and caspase 9 activations. Moreover, upon LPS stimulation, overexpression of TroBcl2 suppressed the activation of several apoptosis-related genes, such as BOK, caspase-9, caspase-7, caspase-3, cytochrome c, and p53. Furthermore, knockdown of TroBcl2 significantly increased the expression of those apoptosis-related genes. In addition, TroBcl2 overexpression or knockdown induced or inhibited, respectively, the transcription of NF-κB and regulated the expression of genes (such as NF-κB1 and c-Rel) in the NF-κB signaling pathway as well as the expression of the downstream inflammatory cytokine IL-1β. Overall, our study suggested that TroBcl2 performs its conserved anti-apoptotic function via the mitochondrial pathway and may serve as an anti-apoptotic regulator in T. ovatus.

Expression of p38MAPK and its regulation of apoptosis under high temperature stress in the razor clam Sinonovacula constricta

p38MAPK is a key branch of the MAPK (mitogen-activated protein kinase) pathway that plays an important role in physiological processes such as apoptosis, cell proliferation and growth. In this experiment, we screened and identified one p38MAPK gene in the razor clam Sinonovacula constricta, which encoded 359 amino acids and was widely expressed in various adult tissues. After 24 h of high temperature stress at 34 °C, the transcript expression of p38MAPK showed significant changes in all tested tissues. In particular in the gill and hepatopancreas tissues, where the expression increased 1.81 and 7.83 times compared with the control group, respectively (P < 0.01). Furthermore, we examined the expression of the apoptosis suppressor gene Bcl-2 and pro-apoptosis gene Bax by knock-down of p38MAPK with dsRNA interference in the gill and hepatopancreas tissues. The obvious up-regulation expression of Bcl-2 and significant suppression of Bax were observed, respectively (P < 0.01). Moreover, the TUNEL staining technique was used to detect apoptosis before and after interference. The degree of apoptosis in the gill and hepatopancreas tissues was reduced after interference with p38MAPK, and the ROS content was significantly reduced (P < 0.01). The results suggested that p38MAPK had a regulatory role in the heat tolerance of razor clams.

Grass carp (Ctenopharyngodon idellus) PIAS1 inhibits innate immune response via interacting with STAT1

Protein inhibitor of activated signal transducer and activator of transcription (PIAS) family protein involved in gene transcriptional regulation acts as negative regulator in Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway. But until now, the roles of PIAS in fish are not clear. In this study, we identified the two mammalian PIAS1 orthologs from Ctenopharyngodon idellus, namely CiPIAS1a and CiPIAS1b, respectively. They can respond to the stimulation from Polyribocytidylic acid (Poly I:C), Grass Carp Reovirus (GCRV) and Lipopolysaccharides (LPS) respectively, so we suggested that they could participate in interferon (IFN)-mediated antiviral and antibacterial immune response. The subcellular localization and nuclear cytoplasm extraction showed that CiPIAS1a and CiPIAS1b were mainly distributed in the nucleus. In addition, Co-IP showed that they separately inhibited the phosphorylation of STAT1 via interacting with it, which leads to the reduction of IFN1 expression.

IRF9 promotes apoptosis and innate immunity by inhibiting SIRT1-p53 axis in fish

As a NAD⁺-dependent deacetylase, SIRT1 is widely involved in apoptosis and cellular inflammation via multiple pathways such as p53, NF-кB and STAT. More and more studies have shown that p53 is the first non-histone deacetylation target of SIRT1. SIRT1-p53 axis thus plays an important role in mammalian cells. IRF9 is an important member of interferon regulator factor family and performs an important role in innate immunity against foreign virus invasion. More importantly, human IRF9 can suppress the SIRT1-p53 axis. However, the functions and relationship between IRF9 and SIRT1-p53 axis are rarely studied in fish. To this end, we made a preliminary research on the functions of grass carp (Ctenopharyngodon idella) IRF9, SIRT1 and p53 in apoptosis and innate immunity. Firstly, we cloned and identified the ORF of SIRT1 (named CiSIRT1, MN125614) from C. idella and demonstrated that CiIRF9 promoted apoptosis, while CiSIRT1 inhibited apoptosis by flow cytometry and TUNEL experiments. Next, we found the interaction between CiSIRT1 and Cip53 in vivo by co-immunoprecipitation experiments. Moreover, the colocalization analysis also showed CiSIRT1 and Cip53 were mainly distributed in nucleus. Thirdly, we got a conclusion that CiIRF9 can repress the expression of CiSIRT1, implying that CiIRF9 regulates CiSIRT1-p53 axis. Finally, CiSIRT1 mRNA level was significantly up-regulated and the expression reached the highest level at 24 h post poly (I:C) stimulation in CIK cells. So, CiSIRT1 may exert an important function in innate immunity. Furthermore, we found CiSIRT1 down-regulated the expression of CiIFN1. In summary, CiIRF9 promotes apoptosis and innate immunity by inhibiting SIRT1-p53 axis. These findings will provide a new theoretical basis for the research on teleost innate immunity.

Grass carp (Ctenopharyngodon idella) IRAK1 and STAT3 up-regulate synergistically the transcription of IL-10

In vertebrates, IL-10 is an anti-inflammatory factor that serves as a key inhibitory role in a wide range of immune responses. IRAK1 (IL-1 receptor-associated kinase 1), a key molecule in the inflammatory signal of IL-1R/TLR, plays an important pivotal role in regulating the autoimmunity of body. STAT3 (Signal transducer and activator of transcription 3) activated by IRAK1 participates in inflammation, tumorigenesis, metabolic disorders and immune response. Under the stimulation of LPS, IRAK1 enters the nucleus to form a dimer with STAT3 and regulates the expression of IL-10. However, the relationship between fish IRAK1 and STAT3 has not been reported. To explain the anti-inflammation in fish, we amplified and identified the complete open reading frame of grass carp IRAK1 (CiIRAK1) and STAT3 (CiSTAT3) based on the existing sequences. The expression of CiIRAK1 and CiSTAT3 were up-regulated significantly under the stimulation of LPS. This result suggests that both CiIRAK1 and CiSTAT3 may be involved in LPS-induced TLR4 pathway. The subcellular localization experiment revealed that CiIRAK1 is distributed in cytoplasm and enters nucleus after LPS stimulation. CiSTAT3 is distributed in both cytoplasm and nucleus with or without LPS stimulation. Immunoprecipitation assay revealed that CiIRAK1 interacted with CiSTAT3 under LPS stimulation. However in absence of LPS stimulation, CiIRAK1 and CiSTAT3 cannot interact with each other. Subsequently, immunofluorescence colocalization experiment further proved the interaction of CiIRAK1 and CiSTAT3 in nucleus under LPS stimulation. The dual luciferase reporter assays indicated that the binding of CiIRAK1 and CiSTAT3 synergistically enhanced the activity of CiIL-10 promoter.