Identifying the downstream effectors of E2F7 in squamous cell carcinoma (SCC) cells. Homo sapiens

Advanced head and neck squamous cell carcinomas (HNSCC) are frequently drug resistant and have a mortality rate of 40%. We have previously shown that E2F7 may contribute to drug sensitivity. In the present study, we conducted an –omics screen to identify factors that were responsible for E2F7-dependent resistance to anthracyclines by HNSCC. We provide, in vitro, in vivo and patient data that identifies the existence of a novel E2F7/Sphingosine kinase 1/Sphingosine-1-phosphate/AKT axis that regulates sensitivity to anthracyclines in HNSCC. Specifically, we show that E2F7-dependent sensitivity to doxorubicin occurs via induction of the sphingosine kinase 1/AKT axis. We also show that pharmacological inhibition of Sphingosine kinase 1 or AKT sensitizes SCC cells to the cytotoxic actions of doxorubicin in vitro and in vivo. Combined, these findings highlight a novel mechanism through which SCC cells acquire resistance to anthracyclines and identify specific pharmacological combinations that could be used to treat SCC. Overall design: Duplicate total RNA isolated from i) untreated, KJD cells, ii) 1µM doxorubicin-treated KJD cells, iii) control plasmid (pcDNA3) transfected, untreated KJD cells, iv) control plasmid (pcDNA3) transfected, 1µM doxorubicin-treated KJD cells, v) E2F7 expression plasmid transfected, untreated KJD cells, vi) E2F7 expression plasmid transfected, 1µM doxorubicin-treated KJD cells, vii) untreated, SCC25 cells, viii) 1µM doxorubicin-treated SCC25 cells, ix) control siRNA (GFPsiRNA) transfected, untreated SCC25 cells, x) control siRNA (GFPsiRNA) transfected, 1µM doxorubicin-treated SCC25 cells, xi) E2F7siRNA transfected, untreated SCC25 cells, xii) E2F7siRNA transfected, 1µM doxorubicin-treated SCC25 cells were hybridised to an RNA microarray to identify genes which are downstream of E2F7 and regulate chemosensitivity in SCC.