Apoptin is a protein encoded by the chicken anemia virus and can cause apoptotic cell death. In this study, a secretory protein was designed by adding a secretory signal to the N-terminal of TAT-Apoptin. The study demonstrated that the SP-TAT-Apoptin induces apoptosis only in malignant cells, and its secretory property might greatly increase its potency for cancer therapy in vivo.
New approaches in cancer therapy that facilitate selective targeting of cancers have been emerging in recent years. Apoptin represents a new anti-cancer tool in such new approaches with great potentials. Two routes can be taken using Apoptin or its encoding cDNA, i.e. as protein therapy or gene therapy.
A research team led by Prof. Duan from Life Sciences Institute of Northwest University used molecular biology,to generated a cDNA construct of SP-Tat-Apoptin fusion. Cancer cells transfected with this construct would express the recombinant Apoptin and apoptosis would be induced in them. By incorporating a synthetic signal peptide authors also expected Apoptin to be secreted outside of the transfected cells as Tat-Apoptin fusion protein and re-enter adjacent untransfected HepG2 cells, enabling the construct to act as both protein and gene therapeutic agent and increasing the potency of Apoptin in cancer therapy.
Having a synthetic signal peptide, the recombinant Apoptin was able to be secreted outside of the transfected cells and re-enter adjacent untransfected HepG2 cells. The recombinant protein was detected in the cytoplasm in HepG2 and HUVEC cells shortly after co-culture of the cells with the cell-free supernatant of the transfected CHO cell culture, indicating the secreted Tat-Apoptin fusion protein contained in the CHO cell culture media was able to enter these cells. The fusion protein was later found in the nucleus in HepG2 cells and induced HepG2 cell apoptosis.
The new secretory characteristic increased the possibility of Apoptin being used in cancer gene therapy. However, there are still a large number of unanswered questions regarding the mechanisms and therapeutic usage of Apoptin, and further studies are certainly required.
There are more HCC cell line used to confirm the results in our study, for example, Bel-7402 HCC cell line. The result about Bel-7402 will be discussed in future. Meanwhile in HUVEC cells, SP-Tat-Apoptin remained in the cytoplasm and no induction of apoptosis above the background level was observed.
- Han SX, Ma JL, Lv Y, Huang C, Liang HH, Duan KM. Secretory Tat-Apoptin fusion protein induces apoptosis in hepatocellular carcinoma HepG2 cells. World J Gastroenterol, 2008; 14(23): 3642-3649 [link]
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