Abstract
BACKGROUND: mac25 is a follistatin (FS)-like protein that has a growth-suppressing effect on a p53-deficient osteosarcoma cell line (Saos-2). The protein exhibits a strong homology to FS, an activin-binding protein, and part of its sequence includes the consensus sequence of the member of the Kazal serine protease inhibitor family. MATERIALS AND METHODS: Localization of mac25 protein was analyzed using mac25 protein fused with green fluorescent protein (GFP). Recombinant mac25 protein was expressed in E. coli and purified. The recombinant mac25 protein was added in culture medium for analysis of growth suppression and cell cycle analysis. Binding of mac25 protein to activin A was studied by immunoprecipitation and Western blots analysis. RESULTS: mac25 protein was localized in the cytoplasm and secreted into culture medium. Addition of recombinant mac25 protein (10-7 M) into the culture medium induced significant suppression of the growth of human cervical carcinoma cells (HeLa) and murine embryonic carcinoma cells (P19), as well as osteosarcoma cells (Saos-2). mac25 protein was co-immunoprecipitated with activin A, a result that suggests that mac25 may be a secreted tumor-suppressor that binds activin A. CONCLUSION: mac25 exhibits homology to insulin-like growth factor-binding proteins (IGF-BPs) and to fibroblast growth factor receptor. The multi-functional nature of mac25 protein may be important for growth-suppression and/or cellular senescence.
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