Effect of nutrient stress on stem cell transcription factor NANOG in ovarian cancer cells

Abstract

Background: Ovarian cancer is one of the most lethal gynaecological cancers in the world. Due to the lack of effective screening strategies, it is usually diagnosed at late stage. Recurrent chemoresistant disease often develops despite positive initial response to therapy. Targeting ovarian cancer stem cells (CSCs) have become the goal of many cancer researchers as they are known to be associated with cancer initiation, proliferation and therapeutic resistance. NANOG is one of the stem cell transcription factors crucial for maintenance of self-renewal and pluripotency of stem cells. It has been found highly expressed in many cancers. A number of studies suggested that cancer cells are capable of reprogramming their metabolism in response to different nutrient conditions (e.g. glucose and glutamine restriction) to support growth, but there are very little or no studies regarding the involvement of NANOG in nutrient stress response. Therefore, we have sought to investigate how nutrient stress affects NANOG level in ovarian cancer in vitro. Materials and methods: This study investigated the expression level of NANOG in an ovarian cancer cell line, OVCAR-3, under full, glucose-free and glutamine-free medium at 0, 24, 48 and 72 hours. Both protein and mRNA of NANOG at various time points were collected and their expression levels were measured by Western Blot analysis and quantitative real-time polymerase chain reaction (qPCR) respectively. Results: Our results demonstrated that NANOG protein expression level was increased in OVCAR-3 under glutamine deprivation, in comparison with nutrient-rich and glucose-free conditions. This might contribute to the increase number of cells over time. Abnormal morphology of OVCAR-3 was observed in glucose-deprived condition despite overexpression of NANOG mRNA was demonstrated. Conclusion: The stem cell transcription factor, NANOG of ovarian cancer cells may be involved in coping with nutrient stress, in particularly glutamine restriction. NANOG-mediated mechanism may be activated to sustain cell proliferation, through reprogramming of metabolism. Further studies will be worthwhile to elucidate the underlying mechanism of NANOG in the proliferation and survival of ovarian cancer cells under nutrient stress.