Cloning, characterization and expression of a cDNA encoding a granulin-like polypeptide in Ciona savignyi

Previous study in our laboratory confirmed that a novel polypeptide, CS5931 derived from Ciona savignyi possesses potent antitumor activity. In the present study, the full length cDNA of CS5931 precursor, termed Cs-pgrn-1 was cloned. The complete cDNA sequence of this gene consists of 685 bp containing an open reading frame (ORF) of 522 bp (173 amino acid residues). In silico analysis revealed that the polypeptide consists of two identical domains, similar with granulin (GRN) found in other species, and each of the domain encodes a polypeptide identical with CS5931. Phylogenetic analysis confirmed that CS5931 shares high homology with Ciona intestinalis GRN and is conserved during evolution. The polypeptide also shows high similarity with human GRN A, B, and C. Prediction of 3D protein structure revealed the 3D structure of CS5931 is very similar with human GRN A. The CS5931 was expressed using a prokaryotic expression system and the purified polypeptide inhibited the growth of several tumor cell lines in vitro via apoptotic pathway. Our study revealed that CS5931 has the potential to be developed as a novel antitumor agent.