Role of Survivin and Hexokinase II in the regulation of Autophagy and Apoptosis in Oral Squamous Cell Carcinoma

Abstract

Survivin, an inhibitor of apoptosis and hexokinase II, a key enzyme in glycolysis are under-expressed in normal oral tissue; while they are over-expressed in oral squamous cell carcinoma (OSCC). Previous studies in our lab have shown a direct correlation between survivin and hexokinase II, using bromo-pyruvic acid, a known hexokinase II inhibitor. Additionally, it has also been shown that there is an increase in the expression of these two biomarkers with the increase in severity of premalignant lesions. These data were obtained from our patient database at Oral Pathology Consultants (OPC) which was compared to the Maryland Cancer Registry (MCR) for a cancer match. Based on this previous work, we decided to study two of the cancer hallmarks in OSCCs; dysregulation of apoptosis and altered cellular metabolism, and molecules associated with them; survivin and hexokinase II. Interestingly, survivin was found to be over-expressed in 80% of OSCCs. Hence, our hypothesis was that in cells during survivin over-expression, treatments with DNA damaging agents will lead to induction of autophagy in OSCCs. To prove this hypothesis, two well known DNA damaging drugs, cisplatin and paclitaxel were used. The basic aim of the study was to down-regulate survivin and study the effect of this down-regulation on autophagy proteins, beclin-1 and mammalian light chain protein kinase, LC3 (autophagy marker). Using a premalignant cell line (Leuk-1) and malignant cell lines (SCC 9 and SCC 25), we have shown down-regulation of survivin using cisplatin and paclitaxel. Survivin is known to inhibit caspases, hence its down-regulate is likely to activate the process of apoptosis. Our western blot results represent down-regulation of beclin-1 as well as the active form of LC3, LC3-II. However, beclin-1 forms a complex with anti-apoptotic proteins, Bcl-2/xL and its down-regulation with chemotherapeutic drugs disturbs the complex, increasing the loss of mitochondrial membrane integrity and ultimately apoptosis. Also, LC3 is a high turn-over protein which can be incorrectly reflected on a western blot. However, further validation of the processes activated due to beclin-1 and LC3 down-regulation will raises a strong possibility of cross-talk between autophagy and apoptosis. Further, literature studies have shown that activation of one signaling pathway regulates key players at transcription and translational levels, which in turn activate or down-regulate other signaling pathways. Our findings support the novel role of the survivin/hexokinase II axis in the regulation of autophagy and apoptosis, in both dysplastic oral lesions and in OSCC.