Serum Starvation Induces a Rapid Increase of Akt Phosphorylation in Ovarian Cancer Cells

Background Cellular stress responses can prevent cell death and help cells to survive in adverse environments. Such responses are important for cancer cells, which are often exposed to cellular stressors such as growth factor deprivation. Depletion of growth factor stimulation may occur in situations such as: metastasis when cancer cells encounter a poorly vascularized environment, angiogenesis inhibitor treatment to reduce blood supply to the tumor or solid tumors in which the central part is deprived of adequate nutrient supply. In vitro , serum starvation is commonly used to mimic growth factor deprivation to reduce activation of kinases under growth factor control, such as Akt. Akt is an oncogene that is activated by the growth factor receptor/PI3K/PDK1 pathway via phosphorylation at Thr 308 to promote cell proliferation and inhibit apoptosis. Hyperactivation of Akt has been shown to promote resistance to first line platinum therapy in ovarian cancer. The canonical Akt activation pathway can be modulated by angiogenesis inhibitors, which are in clinical trials to treat platinum resistant ovarian cancer patients, by reducing tumor blood supply to decrease Akt activation. Previous research suggests that calcium/calmodulin‐dependent protein kinase kinase 2 (CaMKK2) can directly phosphorylate Akt at Thr 308 in a PDK1 independent manner. This suggests that Akt can maintain its activity during serum starvation through multiple mechanisms helping cancer cells to survive stressful conditions. The objectives of the present studies were to investigate whether Akt was activated by serum deprivation and to evaluate the potential role of the PI3K/PDK1/Akt and CaMKK2/Akt pathway in this process. Methods OVCAR‐3 cells were serum starved for a series of times, then Akt phosphorylation at Thr 308 and expressions levels of CaMKK2 and PDK1 were assessed by Western Blotting. siRNA mediated knockdown of PDK1 and/or CaMKK2 were used to investigate the role of PI3K/PDK1/Akt and CaMKK2/Akt pathway respectively in serum starvation‐induced cellular responses. Results Serum starvation increased Akt phosphorylation up to fold at Thr 308 in a time dependent manner in OVCAR‐3 cells. Akt phosphorylation was associated with changes in the expression levels of CaMKK2 and PDK1. Current studies are in process using knockdown of CaMKK2 and/or PDK1 to assess their roles in serum deprivation‐induced Akt phosphorylation. Conclusions Serum deprivation in cell culture mimics the cellular stress faced by tumor cells in vivo . We used this model to evaluate the cellular stress response in ovarian cancer cells and observed an increase in Akt phosphorylation as well as changes in expression of its upstream activators CaMKK2 and PDK1. We conclude that Akt activation may be important for cancer cells including ovarian cancer cells to survive stressful environments through multiple activation pathways. Support or Funding Information University at Buffalo Foundation