The Effect of Bacterial Peptide p28 on Viability and Apoptosis Statusof P53-null HeLa Cells

Despite all the efforts for discovery of efficient anti-cancer therapeutics, cancer is stilla major health concern worldwide. p28 is a bacterial small peptide which has been widelyinvestigated due to its preferential cell internalization and anti-cancer activities. Intracellularly,p28 offers its anti-cancer traits by impeding the degradation of tumor-suppressor protein "p53".In this study, we investigated the potency of p28 in inducing apoptosis or decreasing cellviability in p53-null "HeLa" cell line.

The coding sequence for p28 peptide was obtained from Pseudomonas aeruginosaby PCR amplification of the p28 gene. The coding gene was cloned in pET-28a vector andtransformed into E. coli bacterial host. Subsequently, the expressed peptide was purified usingNi-NTA chromatography system and introduced into the target cells. The anti-proliferative andapoptotic activity of p28 on HeLa and HEK-293 cells were investigated using MTT and PEAnnexinV Flowcytometry assays.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Westernblotting confirmed the expression of p28 peptide in the bacterial host. Bradford assay revealeda concentration of 0.05 mg/mL for the purified p28. MTT assay of cells treated with p28 atconcentrations of 0, 0.5, 1, 2 and 2.5 μM indicated 24h viability values of 97%, 89%, 88%,87% and 84% for HeLa cells, respectively. Data obtained from flowcytometry analyses revealed24h apoptosis rate of 7.17%, 8.05%, 8.63% and 8.84% for HeLa cells treated with 0, 0.5, 1,and 2 μM p28, respectively.

MTT and flowcytometry apoptosis assays suggest no statistically significant effectof p28 on the viability and apoptosis status of p53-null HeLa cells when results compared todata obtained from HEK-293 cells (P > 0.05). These results imply that anti-cancer efficacy of p28is directly dependent on the presence of p53, suggesting p28 as an inappropriate therapeuticagent for treatment of cancers with negative p53 status.