Gene expression profiling in mouse fibroblast tumors with overexpression of the homeoprotein SIX1

Six1 is a developmental transcriptional regulator frequently overexpressed in human tumors. Recent results also show that SIX1 acts as a repressor of cell senescence, an antiproliferative response with key roles in tumor suppression, among other physiological and pathological settings. Here, we set to study the impact of SIX1 gain of function in transformation and tumorigenesis of fibroblasts, in connection with senescence. Using transcriptomic, histological, and functional analyses in murine cells and tumors of fibroblast origin, we show that SIX1 has a strong pro-tumorigenic action in this model, linked to the repression of a senescence-related gene signature and the activation of cellular plasticity, mediated at least in part by direct transcriptional regulation of the stemness factor Sox2. Moreover, functional analyses with human glioma cell lines also show that SIX1 controls SOX2 expression, senescence and self-renewal in this model. Collectively, our results support a general link of SIX1 with senescence and SOX2-mediated cell plasticity in tumors.