Identification of protease inhibitors in the softshell clam (Mya arenaria) and effects of disseminated sarcomas

M. Faisal, DVM, PhD a E. Elsayed, PhD a, and S.M. McLaughlin, PhD b

aDepartment of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI, b National Oceanic and Atmospheric Administration, National Ocean Service, Cooperative Oxford Laboratory, Oxford, MD

Protease inhibitors (PI), a group of proteins believed to play a role in host defense mechanisms against infections and proliferative diseases, have been recently identified in bivalve mollusks. In this study, plasma of the softshell clam was assessed for protease inhibitory activities and the effect of sarcoma progression on PI activities examined. Plasma samples from non-sarcomatous and sarcomatous clam groups were analyzed for inhibitory activities against four proteases representing all mechanistic classes: papain (cysteine protease), pepsin (aspartic protease), thermolysin (metalloprotease), and trypsin (serine protease). Levels of PI activities were measured in a spectrophometer using a hide power azure assay. Inhibitory activities were found in plasma of non-sarcomatous clams against all tested proteases. Clams with early stages of sarcoma showed a non-significant decrease in PI levels. Clams with advanced stages of sarcoma showed a significant decrease in the ability to inhibit trypsin and papain, while the PI activity levels against aspartic and metalloprotease were completely exhausted. Methylamine suppression of plasma inhibitory activity in clasm with early sarcomas was lost in clams with advanced sarcomas. Our study provides evidence of PI in softshell clam plasma which belong to both active site and α2-macroglobulin activities. Moreover, we found that PI activities in softshell clam plasma are modulated by different sarcoma stages. In vertebrates, there is increasing data regarding the involvement of PI in surveillance against tumor progression. The role played by PI in malignancy progression in softshell clams remains to be elucidated; however, the possibility of the involvement of PI in surveillance against sarcoma is expected.

KEY WORDS: Proteases, mollusks, immunity, neoplasia.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Environment and Occupation.