Over the years our laboratory has been working on understanding the role of intracellular redox status on cell death and survival signaling in tumor cells, using a variety of model systems, such as receptor-mediated death signaling, drug-induced apoptosis, oncogene-induced cell proliferation/carcinogenesis, anti-apoptotic members of the Bcl-2 family, and glucose deprivation-induced apoptosis. Results obtained from these studies have challenged the age-old dogma linking intracellular reactive oxygen species (ROS) exclusively to cell and tissue damage and death. Through these set of studies, we provide convincing evidence that the effect of cellular redox status on cell fate decisions is a function of a tight balance between intracellular superoxide (O2-) and hydrogen peroxide (H2O2), the two major ROS species. A slight increase in intracellular O2-inhibits cell death signaling on the one hand and stimulates cell proliferation on the other. This has been demonstrated using models of Ras and Bcl-2-mediated oncogenesis. In the quest to decipher the mechanism underlying the pro-oxidant activity of the death inhibitory protein Bcl-2, we have recently unraveled novel function of Bcl-2 in stimulating mitochondrial oxygen consumption and cytochrome C oxidase (complex IV of electron transport chain) activity, and identified novel interacting partners of Bcl-2 within the mitochondria. The biological relevance of this/these interactions, specifically in terms of the redox-related oncogenic activity of Bcl-2 and its effect on mitochondrial physiology, is the focus of our ongoing studies.
Contrary to the pro-survival activity of O2-, an increase in intracellular H2O2, invariably observed during exposure of tumor cells to anti-cancer drugs, engages and amplifies mitochondrial death pathway via pH-dependent conformational change and activation of the pro-apoptotic Bcl-2 family protein, Bax. Of late, we have extended these studies to death signaling induced via ligation of the death receptors DR4 and DR5 (TRAIL receptors). We provide evidence that TRAIL sensitivity of tumor cells could be significantly amplified via manipulating the cellular redox status. Interestingly, we have identified a potential intracellular target of ROS-mediated regulation of TRAIL signaling and our ongoing efforts are directed at identifying the transcription factor responsible for redox dependent expression of this protein, which could have tremendous potential for enhancing death sensitivity of TRAIL refractory tumors. Along similar lines, we are investigating the activity of novel small molecules as sensitizers of TRAIL-mediated apoptosis in established cell lines as well as in clinical samples. To that end, our preliminary data on cells obtained from lymphoma patients (collaboration with Dr. Thomas Loh, NUH), strongly corroborate these findings. As an extension of these studies, we are also investigating the role of intracellular ROS in the process of autophagy, with specific focus on the role of c-terminal Jun kinase (JNK) and PI3K pathways. Our preliminary studies, using a novel small molecule compound, provide interesting clues into the connection between autophagy and apoptosis. Deciphering the molecular cross talk between these pathways is the current focus of these investigations. Other areas under study related to cellular redox status include the biological activity of flavonoids (in particular Resveratrol and its derivatives), role of ROS in cancer stem cell self-renewal/differentiation (collaboration with Dr. Carol Tang, NNI, Singapore), redox proteomics, role of ROS in PPAR-gamma ligand-induced apoptosis and in casein kinase II-mediated inhibition of apoptosis.
Shazib Pervaiz (Principal Investigator) phssp@nus.edu.sg +65-6874 6602