Prostate apoptosis response-4 (Par-4) is a tumor-suppressor protein that induces apoptosis in cancer cells, but not in normal cells. The cancer-specific pro-apoptotic action of Par-4 is encoded in its centrally located SAC domain. In this study, to further enhance the anti-cancer effect of Par-4 in order to overcome the limitations of peptide therapy, a recombinant adeno-associated virus was constructed using the following strategies: the secretory expression of therapeutic peptide, a HA2TAT-mediated cytosolic delivery technique, and an adeno-associated virus gene transfer system. To test the hypothesis that Par-4 has an additive bystander effect as an anti-cancer therapy, we designed a secretory protein by adding a secretory signal peptide NT4(Si) to the Par-4 SAC-HA2TAT peptide gene sequence [NT4(Si)-Par-4 SAC-HA2TAT]. The results indicated that, compared to the normal NIH3T3 cell line, AAV-NT4(Si)-Par-4 SAC-HA2TAT significantly suppressed cell growth and induced rapid cell death in HepG2 cells in a time-dependent manner through successful gene transfer and secretory expression of therapeutic peptide at 48 h post-transfection. In addition, the secretory properties of Par-4 may greatly increase its effectiveness in cancer therapy when delivered in vivo.

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