Overexpression, purification, molecular characterization and the effect on tumor growth of ribosomal protein L22 from the Giant Panda (Ailuropoda melanoleuca).

The ribosomal protein L22 (RPL22) protein belongs to the L22E family of ribosomal proteins. It is located in the cytoplasm. The purpose of this paper was to explore the structure and anti-cancer function of RPL22 of the Giant Panda (Ailuropoda melanoleuca). The cDNA of RPL22 was cloned successfully from the Giant Panda using RT-PCR technology. We constructed a recombinant expression vector containing RPL22 cDNA and over-expressed it in Escherichia coli using pET28a plasmids. The expression product obtained was purified by using Ni chelating affinity chromatography. The result indicated that the length of the fragment cloned is 414 bp, and it contains an open-reading frame of 387 bp encoding 128 amino acids. Primary structure analysis revealed that the molecular weight of the putative RPL22 protein is 14.74 kDa with a theoretical pI 9.21. The RPL22 gene can be really expressed in E. coli and the RPL22 protein, fusioned with the N-terminally His-tagged protein, gave rise to the accumulation of an expected 20.1 kDa polypeptide. The data showed that the recombinant protein RPL22 had a time- and dose-dependency on the cell growth inhibition rate. The human laryngeal carcinoma Hep-2 cells treated with 0.05-6 μg/ml of RPL22 for 24 h displayed significant cell growth inhibition (p<0.05, n=8) in assayed using MTT compared to the control (untreated) cells. The data indicate that the effect at low concentrations is better than high concentrations, and the concentration of 1.5 μg/ml has the best rate of growth inhibition of 47.70%. The inhibitory rate in mice treated with 1.5 μg/ml RPL22 protein can reach 43.75%. Histology of tumor organs shows that the tissues arranged looser in RPL22 group than those in control group. Meanwhile, there is no obvious damage to other organs, such as heart, lung and kidney. Further research is on going to determine the bioactive principle(s) of recombinant protein RPL22 responsible for its anticancer activity.