Characterization of the tilapia p53 gene and its role in chemical-induced apoptosis

Malathion alters the transcription of target genes of the tumour suppressor tp53 and cancerous processes in Colossoma macropomum: Mechanisms of DNA damage response, oxidative stress and apoptosis

Different classes of pesticides such as fungicides, herbicides, and insecticides, can induce differential expression of genes that are involved in tumorigenesis events in fish, including the expression of tumor suppressor tp53. The degree and duration of the stressful condition is decisive in defining which tp53-dependent pathway will be activated. Herein we evaluate the target genes expression that participates in the regulation pathway of the tumor suppressor tp53 and in the cancerous processes in tambaqui after exposure to malathion. Our hypothesis is that malathion promotes a gene response that is differentially regulated over time, with positive regulation of tp53 target genes related to the apoptotic pathway and a negative regulation of genes that promote antioxidant responses. The fish were exposed to a sublethal concentration of the insecticide for 6 and 48 h. Liver samples were used to analyze the expression of 11 genes using real-time PCR. Overall, the malathion promoted over time increases in tp53 expression and differential expression of tp53 related genes. The exposure resulted in the activation of damage response related genes, caused a positive expression of atm/atr genes. The pro-apoptotic gene bax was up-regulated and the anti-apoptotic bcl2 was down-regulated. Increased expression of mdm2 and sesn1 in the first hours of exposure and no effect on the antioxidant genes sod2 and gpx1 were also observed. We also witnessed an increase in the expression of the hif-1α gene, with no effect on ras proto-oncogene. The extension of this stressful condition accentuated tp53 transcription, and minimized the levels of mdm2, sens1 and bax; however, it down regulated the levels of bcl2 and the bcl2/bax ratio, which indicates the maintenance of the apoptotic response to the detriment of an antioxidant response.

Oxidative stress, DNA damage, and cellular response in hydrogen peroxide-induced cell injury of mud crab (Scylla paramamosain)

Oxidative stress is considered as the toxicity mechanism of environmental stressors on aquatic organisms. This study aims to explore the effects of oxidative stress on physiological responses, DNA damage and transcriptional profiles of the mud crabs Scylla paramamosain. In the present study, mud crabs were injected with 0.1% and 1% hydrogen peroxide (H₂O₂) for 72 h. The results showed that superoxide dismutase and catalase activities significantly decreased after H₂O₂ injection. Malondialdehyde content, H₂O₂ content, aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase activity significantly increased after H₂O₂ injection. Moreover, DNA damage occurred after H₂O₂ injection. Transcriptome analysis showed that 531 and 372 differentially expressed genes (DEGs) were identified after 0.1% and 1% H₂O₂ injection, respectively. These DEGs were mainly involved in the oxidative stress response and immune functions. All these results indicated that oxidative stress could impair both antioxidant defense systems and immune systems. Transcriptome analysis provided valuable information on gene functions associated with the response to oxidative stress in the mud crab.

Bioavailability and impacts of estrogenic compounds from suspended sediment on rainbow trout (Oncorhynchus mykiss)

Numerous environmental pollutants have the potential to accumulate in sediments, and among them are endocrine-disrupting chemicals (EDCs). It is well documented that water-borne exposure concentrations of some potent EDCs, more specifically estrogenic- active compounds (ECs), can impair the reproduction of fish. In contrast, little is known about the bioavailability and effects of sediment-associated ECs on fish. Particularly, when sediments are disturbed, e.g., during flood events, chemicals may be released from the sediment and become bioavailable. The main objectives of this study were to evaluate a) whether ECs from the sediment become bioavailable to fish when the sediment is suspended, and b) whether such exposure leads to endocrine responses in fish. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed over 21 days to constantly suspended sediments in the following treatments: i) a contaminated sediment from the Luppe River, representing a "hotspot" for EC accumulation, ii) a reference sediment (exhibiting only background contamination), iii) three dilutions, 2-, 4- and 8-fold of Luppe sediment diluted with the reference sediment, and iv) a water-only control. Measured estrogenic activity using in vitro bioassays as well as target analysis of nonylphenol and estrone via LC-MS/MS in sediment, water, fish plasma, as well as bile samples, confirmed that ECs became bioavailable from the sediment during suspension. ECs were dissolved in the water phase, as indicated by passive samplers, and were readily taken up by the exposed trout. An estrogenic response of fish to Luppe sediment was indicated by increased abundance of transcripts of typical estrogen responsive genes, i.e. vitelline envelope protein α in the liver and vitellogenin induction in the skin mucus. Altered gene expression profiles of trout in response to suspended sediment from the Luppe River suggest that in addition to ECs a number of other contaminants such as dioxins, polychlorinated biphenyls (PCBs) and heavy metals were remobilized during suspension. The results of the present study demonstrated that sediments not only function as a sink for ECs but can turn into a significant source of pollution when sediments are resuspended as during flood-events. This highlights the need for sediment quality criteria considering bioavailability sediment-bound contaminants in context of flood events.

Ecophysiology, genotoxicity, histopathology, and gene responses of naphthalene injected Colossoma macropomum (Cuvier, 1818) exposed to hypoxia

The present study aimed to evaluate the biological responses of Colossoma macropomum to naphthalene injection and subsequent hypoxia exposure, emphasizing the expression of the tumor suppressor gene tp53. Tambaquis were intraperitoneally injected with naphthalene (50 mg/kg) and, after 96 hours, the fish were transferred to respirometry chambers and, submitted to progressive hypoxia for the determination of critical PO₂. In a subsequent experiment, the fish received an intraperitoneal injection of naphthalene and were kept for 96 hours under normoxia. Successively, fish were challenged with acute hypoxia (PO₂<PO₂ crit) during 6 hours. We observed that the PO₂ crit was not affected by naphthalene injection. Moreover, hematological parameters were modulated only in response to hypoxia. Fish with naphthalene injection plus hypoxia exposure presented altered activity of the GST and CAT enzymes. Exposure to naphthalene also resulted in DNA damages, which was not influenced by hypoxia. Hypoxia accentuated the hepatic lesions caused by naphthalene, as well as it also impaired the transcription of tp53 in naphtalene injected fish, demonstrating the risks of contaminating aquatic environments, especially environments where hypoxic conditions are common and occur on a daily or on seasonal basis, as in the Amazon basin.

Putative histiocytic sarcoma in redfin needlefish Strongylura notata (Beloniformes: Belonidae) in Florida, USA

Redfin needlefish Strongylura notata from Florida coastal waters were observed with unusual neoplastic lesions. Affected specimens were collected from 1 Atlantic estuary (Indian River Lagoon, prevalence = 0.32%, n = 5314) and 2 Gulf of Mexico estuaries (Tampa Bay, prevalence = 0.02%, n = 10762; Charlotte Harbor, prevalence = 0.02%, n = 5112) during routine fisheries-independent monitoring surveys conducted from 1999-2009. Grossly, each lesion manifested as a large (18-30 mm × 20-50 mm), raised (approximately 10 mm), white, creamy, or pinkish nodule on the flank, dorsal trunk, base of the pectoral fin, or head. Multiple small (<5 mm) nodules possessing poorly demarcated borders with neighboring tissues on the external jaw surface and at the base of the teeth were also observed. Histopathologically, neoplastic cells were found in the dermis, beneath the skeletal muscle, and in the soft tissue at the base of teeth of the premaxilla and the dentary jaw processes. Neoplastic cells usually had prominently invaded among the myosepta of the skeletal muscle. Neoplastic parenchymal cells had the basic characteristics of atypical, mononuclear, round, histiocytic cells with an eccentric, reniform nucleus and abundant cytoplasmic vacuolation, while some exhibited bizarre nuclear pleomorphism. Transmission electron microscopy revealed that neoplastic cells had a grooved nucleus and cytoplasmic organelles with rough endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes. Neoplastic cells had possibly metastasized to liver, spleen, and kidney. Positive immunohistochemical staining with Ki67, p53, S-100, and CD163 support neoplastic features and a putative diagnosis of histiocytic sarcoma.

RGNNV-induced cell cycle arrest at G1/S phase enhanced viral replication via p53-dependent pathway in GS cells

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Infection of RGNNV redistributed NPM1, stabilized p53 and inhibited cell proliferation by inducing G1 arrest.

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Infection of RGNNV activated p53-dependent pathway, resulting in G1/S phase cell cycle arrest in host cells and directly impacting viral replication.

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NPM1 knockdown could abrogate RGNNV-induced cell proliferation inhibition and cell cycle arrest.

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Our results revealed that RGNNV infection could perturb the progression of cell cycle via the NPM1-p53 pathway and facilitate virus gene replication.

Nervous necrosis virus (NNV) is a ubiquitous pathogen in the aquaculture worldwide. Little is known about the relationship between NNV virus and host cells. Our studies showed that RGNNV infection could induce cell cycle arrest via activation of p53 signaling in cultured host cells. Infection of RGNNV redistributed NPM1, stabilized p53 and inhibited cell proliferation by inducing G1 arrest. RGNNV infection also led to phosphorylation and accumulation of p53 in a time-dependent manner. Furthermore, RGNNV infection upregulated cyclin-dependent kinase inhibitor 1 A (p21) and downregulated cyclin E and cyclin-dependent kinase 2 (CDK2). The expression of genes in the p53 pathway did not change significantly after p53 knockdown by pifithrin-α during RGNNV infection. However, NPM1 knockdown could abrogate RGNNV-induced cell proliferation inhibition, activation of p53 signaling and cell cycle arrest. In addition, RGNNV infection of the cells synchronized in various stages of cell cycle showed that viral genomic RNA and virus titer were higher in the cells released from G1 phase- or S phase-synchronized cells than that in the cells released from the G2 phase-synchronized or asynchronous cells after 18 h p.i. Therefore, our study reveals that RGNNV infection induces the p53-dependent pathway, resulting in a cell cycle arrest at G1 phase in host cells, which might provide a favorable condition for viral replication.

Benzo[a]pyrene induced p53-mediated cell cycle arrest, DNA repair, and apoptosis pathways in Chinese rare minnow (Gobiocypris rarus)

The p53 pathways play an important role in carcinogenesis. In mammals, p53 and p53 target genes have been extensively studied, but little is known about their functions and regulation in fish. In this study, the cDNA fragments of p53 network genes, including p53, p21, mdm2, gadd45α, gadd45β, igfbp-3, and bax, were cloned from Chinese rare minnow (Gobiocypris rarus). These genes displayed high amino acid sequence identities with their zebrafish orthologs. The mRNA levels of p53 network genes and pathological changes in the liver were determined after adult rare minnow were exposed to 0.4, 2, and 10 µg/L of benzo[a]pyrene (BaP) for 28 days. The results showed that p53, p21, mdm2, gadd45α, and bax mRNA expressions in the livers from males and females were significantly upregulated compared with those of the controls (p < 0.05), but gadd45β and igfbp-3 expression was not significantly changed. Microphotographs revealed enlargement of the cell nuclei and cellular degeneration in males, while atrophy and vacuolization of hepatocytes were observed in females (10 µg/L). These results suggested that BaP induced liver DNA repair and apoptosis pathways and caused adverse pathological changes in rare minnow. The strongly responsive p53 network genes in the livers suggest that rare minnow is suitable as an experimental fish to screen environmental carcinogens. In addition, the p53 network genes in rare minnow could feasibly be used to identify the mechanism of environmental carcinogenesis. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 979-988, 2017.

Identification, characterization and expression analysis of tumor suppressor protein p53 from pufferfish (Takifugu obscurus) after the Vibrio alginolyticus challenge

The tumor suppressor protein p53 plays a critical role in cell cycle, apoptosis and DNA repair. In this study, the full-length pufferfish p53 (Pf-p53) was obtained, containing an open reading frame of 1095 bp, a 5'UTR of 157 bp and a 3'UTR of 285 bp with a poly (A) tail. The Pf-p53 encoded a polypeptide of 364 amino acids with a theoretical isoelectric point of 8.03 and predicted molecular weight of 40.6 kDa. Pf-p53 was ubiquitously expressed in various tissues with a high-level expression in kidney, liver and gill. Vibrio alginolyticus challenge could induce ROS production and disrupt Ca²⁺ homeostasis, subsequently leading to the induction of DNA damage and apoptosis, while the Vibrio alginolyticus-induced oxidative stress can also increase the non-specific immunity. The pufferfish challenged with Vibrio alginolyticus showed a sharp increase of Pf-p53 transcript in liver. Subcellular localization analysis revealed that Pf-p53 was primarily localized in nucleus. Furthermore, overexpression of Pf-p53 in Hela cells could inhibit cell proliferation and the transcriptional activities of the NF-ĸB promoter. Taken together, our results indicated that Pf-p53 may play an important role in the immune response to Vibrio alginolyticus challenge.

Molecular characterization and expression pattern of tumor suppressor protein p53 in mandarin fish, Siniperca chuatsi following virus challenge

In recent years, the tumor suppressor protein p53, which is crucial for cellular defense against tumor development, has also been implicated in host antiviral defense. In the present study, a 1555 bp full-length cDNA of p53 from mandarin fish (Siniperca chuatsi) (Sc-p53) was cloned and characterized. Quantitative real-time PCR assays revealed that Sc-p53 was expressed in all tissues examined, and it was most abundant in the gill and kidney. Recombinant Sc-p53 fused with a His·Tag was expressed in Escherichia coli BL21 (DE3) cells and a rabbit polyclonal antibody was raised against recombinant Sc-p53. In addition, the regulation of Sc-p53 gene expression after experimental viral infection was determined and characterized. The mRNA and protein expression of Sc-p53 were significantly up-regulated in the Chinese perch brain (CPB) cell line and mandarin fish after infection with infectious kidney and spleen necrosis virus (ISKNV). The results showed a biphasic expression pattern of Sc-p53 protein in CPB. However, a different expression pattern of Sc-p53 in response to S. chuatsi rhabdovirus (SCRV) infection was found. The mRNA expression of Sc-p53 was significantly up-regulated in CPB at 6 h and spleen of mandarin fish at 24 h post-infection. The protein expression of Sc-p53 was significantly up-regulated in CPB at 1 h, remained elevated at 4 h, and then decreased to control level at 8 h post-infection by SCRV. All of these data suggested that Sc-p53 plays a critical role in immune defense and antiviral responses.

Expression of bcl-2 and p53 in induction of esophageal cancer cell apoptosis by ECRG2 in combination with cisplatin

AIM

To investigate the mechanisms of induction of apoptosis of esophageal cancer cells by esophageal cancer-related gene 2 (ECRG2) in combination with cisplatin (DDP).

METHODS

Hoechest staining was performed to analyze the effects of single ECRG2 and ECRG2 in combination with DDP on apoptosis of EC9706 cells. The expression levels of p53 and bcl-2 mRNA and protein were determined by RT-PCR and Western blotting, respectively.

RESULTS

The number of apoptotic cells after the treatment with ECRG2 in combination with DDP for 24 hours was more than that after the treatment with single ECRG2. RT-PCR and Western blotting showed that the expression levels of bcl-2 mRNA and protein were both down-regulated, while p53 mRNA and protein were both up-regulated in the cells treated with ECRG2 in combination with DDP compared with those given ECRG2 alone.

CONCLUSION

ECRG2 in combination with DDP can enhance the apoptosis of EC9706 cells, possibly by down-regulating bcl-2 expression and up-regulating p53.

Age at cancer onset in germline TP53 mutation carriers: association with polymorphisms in predicted G-quadruplex structures

Germline TP53 mutations predispose to multiple cancers defining Li-Fraumeni/Li-Fraumeni-like syndrome (LFS/LFL), a disease with large individual disparities in cancer profiles and age of onset. G-quadruplexes (G4s) are secondary structural motifs occurring in guanine tracks, with regulatory effects on DNA and RNA. We analyzed 85 polymorphisms within or near five predicted G4s in TP53 in search of modifiers of penetrance of LFS/LFL in Brazilian cancer families with (n = 35) or without (n = 110) TP53 mutations. Statistical analyses stratified on family structure showed that cancer tended to occur ~15 years later in mutation carriers who also carried the variant alleles of two polymorphisms within predicted G4-forming regions, rs17878362 (TP53 PIN3, 16 bp duplication in intron 3; P = 0.082) and rs17880560 (6 bp duplication in 3' flanking region; P = 0.067). Haplotype analysis showed that this inverse association was driven by the polymorphic status of the remaining wild-type (WT) haplotype in mutation carriers: in carriers with a WT haplotype containing at least one variant allele of rs17878362 or rs17880560, cancer occurred ~15 years later than in carriers with other WT haplotypes (P = 0.019). No effect on age of cancer onset was observed in subjects without a TP53 mutation. The G4 in intron 3 has been shown to regulate alternative p53 messenger RNA splicing, whereas the biological roles of predicted G4s in the 3' flanking region remain to be elucidated. In conclusion, this study demonstrates that G4 polymorphisms in haplotypes of the WT TP53 allele have an impact on LFS/LFL penetrance in germline TP53 mutation carriers.