Microsoft Word - ISJ-2014-365R Uncorrected proofs ISJ 12: 19-21, 2015 ISSN 1824-307X LETTER TO EDITOR Tumors in invertebrates: molluscs as an emerging animal model for human cancer G De Vico, F Carella Department of Biology, University of Naples Federico II, Naples, Italy Accepted December 31, 2014 To the Editor We read with interest the recent paper by Tascedda and Ottaviani (2014) about the occurrence of tumors in invertebrates. In order to further reinforce your statements that “histological and molecular biology studies have proved the existence of tumors in invertebrates” we would like to add to some insights focusing on molluscan neoplasia, an emerging animal model for human cancer (Walker, 2011; Carella et al., 2013). It is known that neoplasia is a pathological process characterized by an overgrowth of a new tissue in the context of a pre-existing one, and consists of atypical cells, a term which incorporates the sum of the differences in morphological, biochemical and functional features of cancer cells relative to normal cells (Carella et al., 2013). Furthermore, neoplastic tissue is characterized by a self-growing, progressive, irreversible and non- finalistic behavior (Dianzani, 2005; De Vico and Carella, 2012). Two predominant types of neoplasia have been reported in marine molluscs, viz. disseminated neoplasia, also called leukaemia or hemic neoplasia (HN), and gonadal neoplasia (Carella et al., 2009). In HN neoplastic cells are represented by atypical hemocytes, which display high nucleus to cytoplasm ratios, diffuse chromatin patterns and pleomorphic nuclei, and usually infiltrate tissues and organs of affected individuals (Auffret and Poder, 1986; Villalba et al., 2001). Since the initial description of the disease (Farley, 1969), its cause has not been clearly defined (Barber, 2004). Viral infection, genetic profile, environmental changes and anthropogenic pollution have been proposed as the causative factors. The prevalence of the disease ranges from 0.5 to 73.3 % , according to the species considered (e.g., Crassostrea virginica, Mytilus spp. and Ostrea edulis) and geographical origins of molluscs. In the affected bivalves HN have been for a long time considered a phenotypically similar proliferative disease in the different shellfish species involved (Walker et al., 2011). However, differences ___________________________________________________________________________ Corresponding author: Gionata De Vico Department of Biology University of Naples Federico II via Mezzocanone, 8, 80134, Naples, Italy E-mail: gionata.devico@unina.it in neoplastic cell morphology, along with descriptions of neoplastic hemocyte subtypes, have frequently contradicted this assumption (Lowe and Moore, 1978; Green and Alderman, 1983). Recently, we described at last two different types of leukemia in two different bivalve species (Mytilus galloprovincialis and Cerastodema edule), showing distinctive morphological and histo-pathogenetic behaviour of cells (Carella et al., 2013). In particular, in mussels, two predominant types of neoplastic cells (A and B) have been described, differently to common cockle where one population of cells have been observed; atypical cells in the respective species also showed a distinct pattern of PCNA (Proliferating Cell Nucler Antigen) expression, nuclear or cytoplasmic (Carella et al., 2013). Such difference could be indicator of a different mechanism of neoplastic cells initiation/progression in early and advanced phase of the disease, respectively, as also strongly supported by Diaz et al. (2013). Gonadal neoplasia is mainly represented by germinoma, which consists of a proliferation of atypical germ cells. Germinoma has been described in several species of marine bivalve molluscs, and most consistently in some populations of Mercenaria mercenaria, Mya arenaria and razor clam, Ensis arcuatus (Barber, 2004; Darriba et al., 2006). In the above species, the prevalence of the disease in a given population could remain underestimated particularly in early cases, where neoplastic cells may still go undetected if the tissue section examined does not happen to contain them (Barber, 2004). In fact, the probability of correctly diagnosing the presence of gonadal neoplasia in molluscs increases with disease progression (Carella et al., 2009). Three evolutive stages of the disease could be observed in M. arenaria (Barber, 1996; 2004), and four stages in Mercenaria spp. (Bert et al., 1993), according to the percentage of gonadal follicles involved and the extent of tissue invasion. Although the aetiology or causes of neoplasia remains unclear, pollution by carcinogenic agents is implicated in the heavily exploited littoral zones of coastal waters. Germinoma have been described also in the gastropod Patella coerulea, accompanied by other gonadal developmental disorders (Carella et al., 2009). Many genes and pathways critically involved in neoplastic transformation and metastasis are 19 evolutionarily conserved in molluscs. Some molecular evidence regarding stress biology and relationships to human biology is available in relation to the function of p53 superfamily members in bivalves. In particular, literature reports p53 (which is among the best known molecules involved in vertebrates carcinogenesis) is demonstrably involved in both bivalve HNs and germinoma (Olberding et al., 2004; St-Jean et al., 2005; Walker et al., 2011) 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 (protein sequences are 67 - 69 % conserved with human p53). However, while in vertebrates p53, p63 and p73 originating from different genes, isoforms of p53 of bivalve molluscs are splice variants of a single gene (Van Beneden et al., 1997; Kelley et al., 2001; Muttray et al., 2005, 2007; Goodson et al., 2006). The p53 protein was detected in tumor cells of molluscs Mytilus edulis, Mytilus trossulus, M. arenaria, Spisula solidissima, Crassostrea rhizophoae and Crassostrea gigas. In particular, a homologue of the human Hsp53 protein was cloned and characterized in M. arenaria affected by HN (Kelley et al., 2001) and presents a domain II-V DNA-ligand, a transactivation domain and a domain MDM2 stored for 73 % compared to the human p53, suggesting that the molecular mechanisms that regulate the transcription of the p53 gene in mollusks are similar to those involved in the human gene (Kelley et al., 2001). Furthermore, in neoplastic hemocytes of M. arenaria, the mortalin (a member of the Hsp70 family whose expression is strongly correlated with the levels of expression of p53 in sick bivalve) (Wadhwa et al., 2002; Siah et al., 2008) sequesters inactivated p53 in the cytoplasm. A similar phenotype, characterized by Hsp70 cytoplasmic sequestration of p53 protein, has been observed in several human cancers (undifferentiated neuroblastoma, retinoblastoma, colorectal and hepatocellular carcinomas, and glioblastoma). Moreover, clam hemocyte cancer is the only animal model thus far investigated where cytoplasmically sequestered wild-type p53 can be reactivated both in vitro and in vivo using both genotoxic and non-genotoxic therapies. Results suggest that mortalin-based cytoplasmic sequestration of wild-type p53 in cancerous clam hemocytes can be reversed by treatment with antineoplastic drugs also employed against similar human diseases and will result either in transcription based apoptosis when the nucleus is accessible or non-transcription-based apoptosis when nuclear access is blocked (Walker et al., 2012). Based on these data, leukemic clam hemocytes is regarded as novel and easily accessible in vivo and in vitro models for human cancers displaying a mortalin-based phenotype, and marine bivalves as the most relevant and best understood model currently available for experimental studies by biomedical and marine environmental researchers. References Auffret M, Poder M. Sarcomatous lesion in the cockle Cerastoderma edule. II. Electron microscopical study. Aquaculture 58: 9-15, 1986. Barber B. Effects of gonadal neoplasms on oogenesis in softshell clams, Mya arenaria. J. Invertebr. Pathol. 67: 161-168, 1996. Barber BJ. Neoplastic diseases of commercially important marine bivalves. Aquat. Living Resour. 17: 449-466, 2004. Bert TM, Hesselman DM, Arnold WS, Moore WS, Cruz-Lopez H, Marelli DC. High frequency of gonadal neoplasia in a hard clam (Mercenaria spp.) hybrid zone. Mar. Biol. 117: 97-104, 1993. Carella F, Restucci B, Maiolino P, De Vico G. A case of germinoma in limpet (Patella coerulea). J. Invertebr. Pathol. 101: 154-156, 2009. Carella F, Figueras A, Novoas B, De Vico G. Cytomorphology and PCNA expression pattern in bivalves Mytilus galloprovincialis and Cerastoderma edule with haemic neoplasia. Dis. Aquat. Org. 105: 81-87, 2013. Darriba S. Razor clams and aquaculture: studies in Galicia (NW Spain). In: Counago SD (ed.), World Aquaculture Society, Aqua 2006, Aqua- Meeting Abstract 797, 2006. De Vico G, Carella F. Argomenti di patologia comparata dei molluschi: aspetti ecologici e sanitari, Loffredo editore, Naples, 2012. Díaz S, Villalba A, Insua A, Soudant P, Fernández- Tajes J, Méndez J, et al. Apoptosis frequency in cockles Cerastoderma edule. J. Invertebr. Pathol. 113: 214-219, 2013. Dianzani UM, Dianzani I, Dianzani U. Istituzioni di patologia generale, Utet Edizioni, Torino, 2005. Goodson MS, Crookes-Goodson WJ, Kimbell JR, Mcfall-Ngai MJ. Characterization and role of p53 family members in the symbiont-induced morphogenesis of the Euprymna scolopes light organ. Biol. Bull. 211: 7-17, 2006. Green M, Alderman DJ. Neoplasia in Mytilus edulis L. from United Kingdom waters. Aquaculture 30: 1-10, 1983. Kelley ML, Winge P, Heaney JD, Stephens RE, Farell JH, Van Beneden RJ, et al. Expression of homologues for p53 and p73 in the softshell clam (Mya arenaria), a naturally-occurring model for human cancer. Oncogene 20: 748- 758, 2001. Lowe DM, Moore MN. Cytology and quantitative cytochemistry of a proliferative atypical haemocytic condition in Mytilus edulis. J. Natl. Cancer Inst. 60: 1455-1459, 1978. Muttray AF, Cox RL, St-Jean S, van Poppelen P, Reinisch CL, Baldwin SA. Identification and phylogenetic comparison of p53 in two distinct mussel species (Mytilus). Comp. Biochem. Physiol. 140C: 237-250, 2005. Muttray AF, Cox RL, Reinisch CL, Baldwin SA. Identification of Delta N isoform and polyadenylation site choice variants in molluscan p53/73-like homologs. Mar. Biotech. 9: 217-230, 2007. Olberding KE, Kelley ML, Butler RA, Van Beneden RJ. A HECT E3 ubiquitin-protein ligase with sequence similarity to E6AP does not target p53 for degradation in the softshell clam (Mya arenaria). Mutat. Res. 552: 61-71, 2004. Siah A, Delaporte M, Pariseau J, McKenna P, Berthe FC. Patterns of p53, p73 and mortalin gene expression associated with haemocyte 20 polyploidy in the soft-shell clam, Mya arenaria. J. Invertebr. Pathol. 98: 148-152, 2008. Walker CW, Van Beneden RJ, Muttray AF, Böttger SA, Kelley ML, Tucker AE, et al. p53 superfamily proteins in marine bivalve cancer and stress biology. Adv. Mar. Biol. 59: 1-36, 2011. St-Jean SD, Stephens RE, Courtenay SC, and Reinisch CL. Detecting p53 family proteins in leukemia cells of Mytilus edulis from Pictou Harbour, Nova Scotia. Can. J. Fish. Aquat. Sci. 62; 2055-2066, 2005. Walker CW. Mortalin in invertebrates and the Induction of apoptosis by wild-type p53 following defeat of mortalin-based cytoplasmic sequestration in cancerous clam hemocytes. In: Kaul SC, Wadhwa R (eds), Mortalin Biology: life, stress and death, Chapter 6, 97 DOI 10.1007/978-94-007-3027-4_6, © Springer Science+Business Media, 2012. Tascedda F, Ottaviani E. Tumors in invertebrates. Inv. Surv. J. 11: 197-203, 2014. Van Beneden RJ,Walker CW, Laughner ES. Characterization of gene expression of a p53 homologue in the sift-shell clam (Mya arenaria). Mol. Mar. Biol. Biotechnol. 6: 116-122, 1997. Villalba A, Carballal MJ, Lopez C. Disseminated neoplasia and large foci indicating heavy haemocytic infiltration in cockles Cerastoderma edule from Galicia (NW Spain). Dis. Aquat. Org. 46: 213-216, 2001. Wadhwa R, Sugihara T, Hasan MK, Taira K, Reddel RR, Kaul SC. A major functional difference between the mouse and human ARF tumor suppressor proteins. J. Biol. Chem. 277: 36665- 36670, 2002. 21