Identification of DeltaN isoform and polyadenylation site choice variants in molluscan p63/p73-like homologues

Transcriptomics of mussel transmissible cancer MtrBTN2 suggests accumulation of multiple cancer traits and oncogenic pathways shared among bilaterians

Transmissible cancer cell lines are rare biological entities giving rise to diseases at the crossroads of cancer and parasitic diseases. These malignant cells have acquired the amazing capacity to spread from host to host. They have been described only in dogs, Tasmanian devils and marine bivalves. The Mytilus trossulus bivalve transmissible neoplasia 2 (MtrBTN2) lineage has even acquired the capacity to spread inter-specifically between marine mussels of the Mytilus edulis complex worldwide. To identify the oncogenic processes underpinning the biology of these atypical cancers we performed transcriptomics of MtrBTN2 cells. Differential expression, enrichment, protein-protein interaction network, and targeted analyses were used. Overall, our results suggest the accumulation of multiple cancerous traits that may be linked to the long-term evolution of MtrBTN2. We also highlight that vertebrate and lophotrochozoan cancers could share a large panel of common drivers, which supports the hypothesis of an ancient origin of oncogenic processes in bilaterians.

Transcriptomic effects of the non-steroidal anti-inflammatory drug Ibuprofen in the marine bivalve Mytilus galloprovincialis Lam

The transcriptomic effects of Ibuprofen (IBU) in the digestive gland tissue of Mytilus galloprovincialis Lam. specimens exposed at low environmental concentrations (250 ng L(-1)) are presented. Using a 1.7 K feature cDNA microarray along with linear models and empirical Bayes statistical methods 225 differentially expressed genes were identified in mussels treated with IBU across a 15-day period. Transcriptional dynamics were typical of an adaptive response with a peak of gene expression change at day-7 (177 features, representing about 11% of sequences available for analysis) and an almost full recovery at the end of the exposure period. Functional genomics by means of Gene Ontology term analysis unraveled typical mussel stress responses i.e. aminoglycan (chitin) metabolic processes but also more specific effects such as the regulation of NF-κB transcription factor activity.

p63 gene structure in the phylum mollusca

Roles of p53 family ancestor (p63) in the organisms' response to stressful environmental conditions (mainly pollution) have been studied among molluscs, especially in the genus Mytilus, within the last 15 years. Nevertheless, information about gene structure of this regulatory gene in molluscs is scarce. Here we report the first complete genomic structure of the p53 family orthologue in the mollusc Mediterranean mussel Mytilus galloprovincialis and confirm its similarity to vertebrate p63 gene. Our searches within the available molluscan genomes (Aplysia californica, Lottia gigantea, Crassostrea gigas and Biomphalaria glabrata), found only one p53 family member present in a single copy per haploid genome. Comparative analysis of those orthologues, additionally confirmed the conserved p63 gene structure. Conserved p63 gene structure can be a helpful tool to complement or/and revise gene annotations of any future p63 genomic sequence records in molluscs, but also in other animal phyla. Knowledge of the correct gene structure will enable better prediction of possible protein isoforms and their functions. Our analyses also pointed out possible mis-annotations of the p63 gene in sequenced molluscan genomes and stressed the value of manual inspection (based on alignments of cDNA and protein onto the genome sequence) for a reliable and complete gene annotation.

Biomarkers and transcription levels of cancer-related genes in cockles Cerastoderma edule from Galicia (NW Spain) with disseminated neoplasia

Disseminated neoplasia (DN) is a pathological condition reported for several species of marine bivalves throughout the world, but its aetiology has not yet been satisfactorily explained. It has been suggested that chemical contamination could be a factor contributing to neoplasia. The aim of the present study was to compare cell and tissue biomarkers and the transcription level of cancer-related genes in cockles (Cerastoderma edule) affected by DN with those of healthy cockles in relation to chemical contaminant burdens. For this, cockles were collected from a natural bed in Cambados (Ria de Arousa, Galicia) in May 2009. The prevalence of DN was 12.36% and 3 degrees of DN severity were distinguished. No significant differences in metal accumulation, non-specific inflammatory responses and parasites were observed between healthy and DN-affected cockles. Lysosomal membrane stability was significantly reduced in cockles affected by DN, which indicates a poorer health condition. Very low frequencies of micronuclei were recorded and no significant differences were detected between DN severity groups. Haemolymph analyses showed a higher frequency of mitotic figures and binucleated cells in cockles affected by moderate and heavy DN than in healthy ones. Neoplastic animals showed significantly higher transcription levels of p53 and ras than healthy cockles and mutational alterations in ras gene sequence were detected. Low concentrations of metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls and phthalate esters were measured in cockles from Cambados. In conclusion, cockles affected by DN suffer a general stress situation and have altered patterns of cancer-related gene transcription. Further studies are in progress to elucidate mechanisms of carcinogenesis in this species.

Identification of relevant cancer related-genes in the flat oyster Ostrea edulis affected by disseminated neoplasia

Disseminated neoplasia (DN), an oyster disease resembling leukaemia, has been reported in a number of species of marine bivalve molluscs. The disease is characterised by a proliferation of abnormal circulating cells of unknown origin resulting in the invasion of tissues and organs, frequently with a fatal end of the affected individuals. To obtain a more comprehensive view of bivalve cancer processes, suppressive subtracted hybridisation (SSH) and quantitative RT-PCR (q-PCR) approaches were combined to investigate changes in the transcriptome of Ostrea edulis haemolymph cells associated to DN. Two SSH libraries were constructed and 587 expressed sequence tags (ESTs) were sequenced, obtaining 329 ESTs which showed expression changes in neoplastic process. Transcription expression analyses (q-PCR) were done for a total of 24 genes that could be relevant in neoplastic process, including genes with role in the regulation of cell cycle, apoptosis or chromosomal defects. Most of those genes had not been reported in association with cancer in non-vertebrate organisms. The over-expression and under-expression of some of those genes in DN-affected oysters was in agreement with observations in vertebrate cancer. The results herein reported contribute to cancer understanding in bivalve molluscs.

Recognition and suppression of transfected plasmids by protein ZNF511-PRAP1, a potential molecular barrier to transgene expression

Nonviral vectors present considerable advantages over viral counterparts in gene transfer. However, the poor expression efficiency of the transfected genes poses a challenge for their use in gene therapy, primarily due to the inability of these vectors to overcome various barriers, including the biological barriers. Here, we report that ZNF511-PRAP1 may be involved in the recognition and inactivation of transfected plasmids. ZNF511-PRAP1 is induced by transfection of plasmid DNA and suppresses the transcription of transfected plasmids. It binds directly to the p21 promoter in transfected plasmids but not the endogenous counterpart. Similarly, ZNF511-PRAP1 suppresses the expression of the green fluorescent protein reporter gene on transiently transfected plasmids but not an integrated red fluorescence reporter gene with the same cytomegalovirus (CMV) promoter. Therefore, ZNF511-PRAP1 is able to differentiate between exogenous/nonintegrated and endogenous/integrated DNA. The suppression by ZNF511-PRAP1 is independent of DNA methylation and can be abolished by trichostatin A (TSA) treatment and knockdown of HDAC2 and/or ZNF511-PRAP1. Furthermore, ZNF511-PRAP1 interacts directly with HDAC2. Our results revealed that transfected plasmids are recognized by ZNF511-PRAP1 and suppressed by a repressor complex comprising ZNF511-PRAP1 and HDAC2 and suggest that ZNF511-PRAP1 could play a role as a potential molecular barrier in nonviral transgene expression.

p53 Superfamily proteins in marine bivalve cancer and stress biology

The human p53 tumour suppressor protein is inactivated in many cancers and is also a major player in apoptotic responses to cellular stress. The p53 protein and the two other members of this protein family (p63, p73) are encoded by distinct genes and their functions have been extensively documented for humans and some other vertebrates. The structure and relative expression levels for members of the p53 superfamily have also been reported for most major invertebrate taxa. The functions of homologous proteins have been investigated for only a few invertebrates (specifically, p53 in flies, nematodes and recently a sea anemone). These studies of classical model organisms all suggest that the gene family originally evolved to mediate apoptosis of damaged germ cells or to protect germ cells from genotoxic stress. Here, we have correlated data from a number of molluscan and other invertebrate sequencing projects to provide a framework for understanding p53 signalling pathways in marine bivalve cancer and stress biology. These data suggest that (a) the two identified p53 and p63/73-like proteins in soft shell clam (Mya arenaria), blue mussel (Mytilus edulis) and Northern European squid (Loligo forbesi) have identical core sequences and may be splice variants of a single gene, while some molluscs and most other invertebrates have two or more distinct genes expressing different p53 family members; (b) transcriptional activation domains (TADs) in bivalve p53 and p63/73-like protein sequences are 67-69% conserved with human p53, while those in ecdysozoan, cnidarian, placozoan and choanozoan eukaryotes are ≤33% conserved; (c) the Mdm2 binding site in the transcriptional activation domain is 100% conserved in all sequenced bivalve p53 proteins (e.g. Mya, Mytilus, Crassostrea and Spisula) but is not present in other non-deuterostome invertebrates; (d) an Mdm2 homologue has been cloned for Mytilus trossulus; (e) homologues for both human p53 upstream regulatory and transcriptional target genes exist in molluscan genomes (missing are ARF, CIP1 and BH3 only proteins) and (f) p53 is demonstrably involved in bivalve haemocyte and germinoma cancers. We usually do not know enough about the molecular biology of marine invertebrates to address molecular mechanisms that characterize particular diseases. Understanding the molecular basis of naturally occurring diseases in marine bivalves is a virtually unexplored aspect of toxicoproteomics and genomics and related drug discovery. Additionally, increases in coastal development and concomitant increases in aquatic pollutants have driven interest in developing models appropriate for evaluating potential hazardous compounds or conditions found in the aquatic environment. Data reviewed in this study are coupled with recent developments in our understanding the molecular biology of the marine bivalve p53 superfamily. Taken together, they suggest that both structurally and functionally, bivalve p53 family proteins are the most highly conserved members of this gene superfamily so far identified outside of higher vertebrates and invertebrate chordates. Marine bivalves provide some of the most relevant and best understood models currently available for experimental studies by biomedical and marine environmental researchers.

Variations in p53-like cDNA sequence are correlated with mussel haemic neoplasia: A potential molecular-level tool for biomonitoring

Several bivalve species, including mussels (Mytilus spp.) and clams (Mya spp.), are susceptible to a leukemia-like disease called haemic neoplasia that has been known to decimate whole populations. Previous studies of molecular processes associated with late stages of this disease have implicated analogs of the p53 tumour suppressor protein family in disease etiology. We detected synonymous single nucleotide polymorphisms (SNPs) in the coding region sequence of p53-like cDNA from Mytilus trossulus (bay mussel) that differ between normal and neoplastic haemolymph. SNPs were located at positions 182, 392 and 821 bp. Most (94%) of the late leukemic animals sampled from cages in Burrard Inlet (British Columbia, Canada) had the same p53-like genotype, C182T G392G C821T, whereas 75% of the healthy animals were homozygous at positions C182C and T821T, independent of the genotype at the 392 bp position. As well, we detected an increased number of allelic variants in the leukemic animals that may arise from separate somatic mutation events in haemocyte precursors or from additional p53-like gene copies in polyploidy. Therefore, detection of these SNPs may provide a useful genetic biomarker for efficient monitoring of mussel population health.

Phylogeny and function of the invertebrate p53 superfamily

The origin of the p53 superfamily predates animal evolution and first appears in unicellular Flagellates. Invertebrate p53 superfamily members appear to have a p63-like domain structure, which seems to be evolutionarily ancient. The radiation into p53, p63, and p73 proteins is a vertebrate invention. In invertebrate models amenable to genetic analysis p53 superfamily members mainly act in apoptosis regulation in response to genotoxic agents and do not have overt developmental functions. We summarize the literature on cnidarian and mollusc p53 superfamily members and focus on the function and regulation of Drosophila melanogaster and Caenorhabditis elegans p53 superfamily members in triggering apoptosis. Furthermore, we examine the emerging evidence showing that invertebrate p53 superfamily proteins also have functions unrelated to apoptosis, such as DNA repair, cell cycle checkpoint responses, compensatory proliferation, aging, autophagy, and innate immunity.

An invertebrate mdm homolog interacts with p53 and is differentially expressed together with p53 and ras in neoplastic Mytilus trossulus haemocytes

The mussel Mytilus trossulus can develop a neoplasia of the haemolymph, which occurs with high frequency (up to 40%) in nature. Associated with this disease are pro-apoptotic tumor-suppressor protein p53 isoforms, which are highly conserved between molluscs and vertebrates. The vertebrate wildtype p53 protein is maintained at low levels by the MDM2 protein in non-stressed cells to prevent undesired apoptosis. Identification of a putative invertebrate MDM-like homolog suggests early evolution of this mechanism of p53 regulation. The M. trossulus MDM homolog consists of a conserved NH(2)-terminal p53 binding domain, an acidic domain with highly conserved phosphorylation sites, and a highly conserved C-terminal RING-finger Zn-binding domain. Although BLAST queries predict this homologue to be more similar to vertebrate MDM2 than to MDM4, phylogenetic analysis suggests that it may be an ancestral form to both vertebrate MDM genes. Using yeast-two-hybrid assays and pull-down assays, we show that this molluscan MDM is able to bind to its p53 counterpart. We also show that MDM expression levels are directly correlated with p53 expression levels in healthy and in neoplastic haemocytes, but not with other p53 isoforms or with the proto-oncogene RAS. The combination of expression levels of five gene transcripts (p53, mdm, ras, Np63/73, and TAp63/73) is significantly correlated with late-stage haemic neoplasia in M. trossulus.

Proteomics identification of azaspiracid toxin biomarkers in blue mussels, Mytilus edulis

Azaspiracids are a class of recently discovered algae-derived shellfish toxins. Their distribution globally is on the increase with mussels being most widely implicated in azaspiracid-related food poisoning events. Evidence that these toxins were bound to proteins in contaminated mussels has been shown recently. In the present study characterization of these proteins in blue mussels, Mytilus edulis, was achieved using a range of advanced proteomics tools. Four proteins present only in the hepatopancreas of toxin-contaminated mussels sharing identity or homology with cathepsin D, superoxide dismutase, glutathione S-transferase Pi, and a bacterial flagellar protein have been characterized. Several of the proteins are known to be involved in self-defense mechanisms against xenobiotics or up-regulated in the presence of carcinogenic agents. These findings would suggest that azaspiracids should now be considered and evaluated as potential tumorigenic compounds. The presence of a bacterial protein only in contaminated mussels was an unexpected finding and requires further investigation. The proteins identified in this study should assist with development of urgently required processes for the rapid depuration of azaspiracid-contaminated shellfish. Moreover they may serve as early warning indicators of shellfish exposed to this family of toxins.

Expression analysis of the molluscan p53 protein family mRNA in mussels (Mytilus spp.) exposed to organic contaminants

In this study, we report the tissue expression analysis of the p53 protein family mRNA in mussels (Mytilus spp.) by means of quantitative RT-PCR. The tissue specific response was evaluated after 24 h exposure to a sublethal benzo[a]pyrene (B[a]P) concentration (75 nM), showing a 2.6 fold induction in digestive gland cells and a dramatic gene down regulation in circulating hemocytes. The comet assay and DNA gel diffusion tests showed significant effects in hemocytes and negligible differences in the digestive gland nuclei, implicating p53 in DNA damage of molluscan hemocytes. Finally, the kinetics of p53 protein family mRNA expression in the digestive gland of animals exposed to B[a]P and crude oil (0.5 ppm) showed partially overlapping trends, characterised by a common down regulation after 1 week exposure. These data should be carefully considered in view of the biological effects of organic pollutants and particularly following spills.

Mass culture and characterization of tumor cells from a naturally occurring invertebrate cancer model: applications for human and animal disease and environmental health

On the northeastern coast of the United States and Canada, Mya arenaria, the soft shell clam, develops a diffuse, hemopoetic tumor (a fatal leukemia-like cancer) resulting from inactivation of p53-like family member proteins.These malignant cells provide a model for an unrelated set of human cancer cells that are also characterized by mortalin-based cytoplasmic sequestration of wild-type p53 tumor suppressor protein (mortalin is the mitochondrial Hsp70 protein). Here we describe methods for mass culture and long-term storage of tumor cells from this cancer. These are the first successful efforts at maintaining malignant cells from any marine invertebrate in vitro. Following passage (subculture), these cultures undergo transition from primary cultures to non-immortalized cell lines that continue to proliferate and do not re-differentiate the normal hemocyte phenotype. We also characterize normal clam hemocytes and the pathology of cancerous clam hemocytes in vitro and in vivo using light and electron microscopy, cyto- and immunocytochemistry, molecular biology, and a phagocytosis assay. Our protocols provide biomedical and environmental researchers with ready access to this naturally occurring cancer model. We discuss the clam cancer model regarding (a) human health and disease; (b) animal health, disease, and aquaculture; (c) environmental health monitoring; and (d) future research directions.

Invertebrate p53-like mRNA isoforms are differentially expressed in mussel haemic neoplasia

Mussels of the genus Mytilus are widely used in environmental monitoring. They can develop a leukaemia-like disease, haemic neoplasia, which could be induced, in part, by environmental stressors. The molluscan p53 tumor suppressor gene family was previously shown to be involved in haemic neoplasia at the protein level. The purpose of this study was the quantification of molluscan p53-like isoforms at the mRNA level in mussels with haemic neoplasia compared to normal controls. The three isoforms monitored were a p53-like, a TAp63/73-like containing an intact transactivation (TA) domain, and an NH(2)-terminally truncated p63/73 isoform termed DeltaNp63/p73-like that lacks the full TA domain. Using a comprehensive data set of 62 individual Mytilus trossulus and reverse transcription real-time PCR, we found that both the p53 and the DeltaNp63/73 isoforms were up-regulated in neoplastic haemocytes compared to normal haemocytes (p<0.0001). In contrast, the mRNA levels of the non-truncated isoform TAp63/73 did not change significantly in mussels with the disease at alpha=0.01 (p=0.0141), in contrast to previous findings at the protein level. Correlations in mRNA levels between the truncated isoform and the full-length isoforms in normal haemocytes were lost in neoplastic haemocytes. The increase in mRNA concentration of the truncated DeltaNp63/73 isoform in molluscan haemic neoplasia is similar to observations in many human cancers and cell lines and underlines the phylogenetically ancient oncogenic role of this isoform.

Molecular cloning of a new member of the p53 family from the Pacific oyster Crassostrea gigas and seasonal pattern of its transcriptional expression level

Like other sessile filter-feeding molluscs, oysters may be exposed in the natural environment to a variety of contaminants. Long-term exposure to pollutants may be one factor affecting prevalence of cancerous-like disorders, such as neoplasia. Environmentally induced alterations in p53 protein expression, in relation to leukemia, have been reported in various mollusc species inhabiting polluted water, suggesting that p53 proteins can also be used as a marker for environmental research. This work reports the cloning and sequencing of a p53-like cDNA in the mollusc bivalve Crassostreagigas. The deduced amino acid sequences of p53 shared a high degree of homology with the homologues from other mollusc species, including typical eukaryotic p53 signature sequences. We examined the p53 transcription expression pattern during the annual cycle in oyster gills and whole soft tissues in four locations along the French coasts. Real-time PCR analysis suggested that strong variations at p53 mRNA level are probably synchronized with the seasonal cycle at the four locations investigated.

DNp73 a matter of cancer: mechanisms and clinical implications

The p53 family proteins carry on a wide spectrum of biological functions from differentiation, cell cycle arrest, apoptosis, and chemosensitivity of tumors. NH2-terminally truncated p73 (referred to as DNp73) acts as a potent inhibitor of all these tumor suppressor properties, implying that it has oncogenic functions in human tumorigenesis. This was favored by the observation that high DNp73 expression levels in a variety of cancers are associated with adverse clinico-pathological characteristics and the response failure to chemotherapy. The actual challenge is the deciphering of the molecular mechanisms by which DNp73 promotes malignancy and to unravel the regulatory pathways for controlling TP73 isoform expression. This review is focused on recent findings leaving no doubt that N-terminally truncated p73 proteins are operative during oncogenesis, thus underscoring its significance as a marker for disease severity in patients and as target for cancer therapy.