Apoptotic Status in Response to Green Tea Polyphenols in p57/KIP2 Expressing Oral Carcinoma Cells

We previously reported that green tea polyphenols (GTPPs) are able to selectively induce cell death in oral squamous carcinoma cell lines, while normal epithelial cells survived by an induction of a cyclin-dependent kinase inhibitory protein (p57/KIP2). But whether p57/KIP2 plays a determinant role for cell survival is unknown. Objective: This study compared the impact of GTPPs in p57-expressing subclones (S1 - S4) and their parental cell line (OSC2), to determine whether p57 expression is required for cell survival when treated with an apoptosis-inducing agent in gradual amounts. Methods: The mitochondrial activities were measured by MTT assay; GTPPs-induced apoptosis was monitored by caspase-3 activity assay and light microscopy. Results: The oral squamous carcinoma cells without p57 expression showed a strong correlation to the apoptotic effects of green tea polyphenols (GTPPs) while the p57-expressing subclones survived incubation with GTPPs. Graphical interpretation further illustrates that the quantity of GTPPs treated is proportional to the increase in cellular apoptosis for carcinoma cells lacking p57/KIP2, whereas p57-expressing subclones presented a greater apoptotic resistance. Conclusion: p57/KIP2 is a crucial factor for cell survival during induction of apoptosis, which could be used as a marker for oral cancer prognosis and chemotherapy.