Esophageal squamous cell carcinoma transcriptome reveals the effect of <i>FOXM1</i> on patient outcome through novel PIK3R3 mediated activation of PI3K signaling pathway

Esophageal squamous cell carcinoma (ESCC) presents poor prognosis, and patients diagnosed with this tumor currently lack target treatments. Therefore, in order to identify potential targets for ESCC treatment, we carried out a transcriptome analysis with ESCC and paired nonmalignant surrounding mucosa samples, followed by a master regulator analysis, and further explored the role of the identified central regulatory genes through <i>in vivo</i> and <i>in vitro</i> assays. Among the transcription factors deregulated/enriched in ESCC, we focused on FOXM1 because of its involvement in the regulation of critical biological processes. A new transcriptome analysis performed with ESCC cell lineage TE-1 showed that the modulation of <i>FOXM1</i> expression resulted in <i>PIK3R3</i> expression changes, whereas chromatin immunoprecipitation assay revealed that FOXM1 was capable of binding onto <i>PIK3R3</i> promoter, thus demonstrating that <i>PIK3R3</i> is a new FOXM1 target. Furthermore, FOXM1 overexpression resulted in the activation of PIK3/AKT signaling pathway through PIK3R3-mediated AKT phosphorylation. Finally, the analysis of the clinic-pathological data of ESCC patients revealed that overexpression of both FOXM1 and PIK3R3 was associated with poor prognosis, but only the latter was an independent prognosis factor for ESCC patients. In conclusion, our results show that FOXM1 seems to play a central role in ESCC carcinogenesis by upregulating many oncogenes found overexpressed in this tumor. Furthermore, <i>PIK3R3</i> is a novel FOXM1 target that triggers the activation of the PI3K/AKT pathway in ESCC cells.