Tumor suppressive function of E2F-1 on PTEN-induced serrated colorectal carcinogenesis

Many human cancers present Phosphatase and tensin homolog (PTEN) deficiency and between 20 and 30% of colorectal tumors show PTEN loss. The transcription factor, E2 promoter binding factor 1 (E2F-1), exhibits tumor promoter or suppressive functions depending on cellular type and tissue context, but its role in the progression and development of colorectal carcinogenesis was largely unknown. Here, using a tamoxifen-inducible PTEN knockout mouse model, we have demonstrated that loss of PTEN leads to the development of colorectal tumorigenesis through the serrated pathway. Next, we studied PTEN loss-driven colorectal lesions in the context of E2F-1 deficiency in vivo. Our results revealed that monoallelic and biallelic absence of E2F-1 led to an increased incidence and progression of serrated tumorigenesis induced by PTEN loss. Finally, we investigated the mechanisms by which double PTEN/E2F-1 deficiency leads to enhanced tumorigenesis. We found that colorectal tumors from PTEN/E2F-1 double knockout mice and the human colorectal carcinoma cell line HT29 with shRNA-mediated downregulation of PTEN and E2F-1 exhibit hyperactivation of the RAS-MAPK pathway, accumulation of DNA damage and resistance to apoptosis. To date, this is the first preclinical study evaluating the effect of genetic deletion of E2F-1 in colorectal malignancies driven by PTEN deficiency. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.