Anti-apoptotic genes are synergistically activated in OVSAYO cells cultured under conditions of serum starvation and hypoxia

The tumor microenvironment is generally hypoxic because of the limited oxygen supply from inefficient or insufficient vasculature. Hypoxic tumor tissues are also poorly supplied with serum components. We have previously demonstrated that expression of the FVII gene is induced in response to hypoxia in ovarian clear cell carcinoma (CCC) cells. This gene activation is synergistically enhanced when cells are simultaneously subjected to serum starvation, and is dependent on the transcription factor Sp1 directly associating with the FVII promoter. We have identified additional genes activated via a similar Sp1-dependent mechanism by conducting cDNA microarray analysis (GSE55565). ICAM1, which encodes intercellular adhesion molecule-1 (ICAM-1), is one such gene. ICAM-1 confers an anti-apoptotic effect upon CCC cells in vitro and promotes growth of CCC tumors. Here we describe the transcriptome analysis performed in our recently published study (Koizume et al., 2015). We further show that autonomous activation of the TNFα–NFκB axis is responsible for the synergistic activation of ICAM1 under hypoxic and serum starvation conditions. This study provides additional information as to how CCC cell survival can be facilitated under conditions of serum starvation and hypoxia.