KRAS Promotes GLI2-Dependent Transcription during Pancreatic Carcinogenesis

Abstract

Aberrant activation of GLI transcription factors has been implicated in the pathogenesis of different tumor types including pancreatic ductal adenocarcinoma (PDAC). However, the mechanistic link with established drivers of this disease remains in part elusive. Here, using a new genetically-engineered mouse model overexpressing constitutively active mouse form of GLI2 and a combination of genome wide assays, we provide evidence of a novel mechanism underlying the interplay between KRAS, a major driver of PDAC development, and GLI2 to control oncogenic gene expression. These mice, also expressing KrasG12D, show significantly reduced median survival rate and accelerated tumorigenesis compared to the KrasG12D only expressing mice. Analysis of the mechanism using RNA-seq demonstrate higher levels of GLI2 targets, particularly tumor growth promoting genes including Ccnd1, N-Myc and Bcl2, in KrasG12D mutant cells. Further, ChIP-seq studies showed that in these cells KrasG12D increases the levels of H3K4me3 at the promoter of GLI2 targets without affecting significantly the levels of other major active chromatin marks. Importantly, Gli2 knockdown reduces H3K4me3 enrichment and gene expression induced by mutant Kras. In summary, we demonstrate that Gli2 plays a significant role in pancreatic carcinogenesis by acting as a downstream effector of KrasG12D to control gene expression.