Loss of Activating transcription factor 3 restricts KRASG12D’s ability to promote PanIN progression through epithelial specific transcriptional regulation

Pancreatic ductal adenocarcinoma (PDAC) is the 3rd leading cause of cancer-related deaths in North America with ~12% survival 5 years after diagnosis. Risk factors for PDAC, including smoking and chronic pancreatitis, trigger the unfolded protein response (UPR) and global loss of Activating Transcription Factor 3 (ATF3), a mediator of the UPR, restricts preneoplastic progression in mice expressing oncogenic KRAS (KRASG12D). Since ATF3 is expressed in multiple cell compartments during PDAC progression, the goal of this study was to determine epithelial-specific roles for ATF3 during pre-neoplastic stages of PDAC. APK and AacinarPK tissue showed restricted neoplasia progression compared to Ptf1acreERT/+KRASG12D/+ mice. Ptf1acreERT/+KRASG12D/+ and APK organoids showed differential gene expression, and morphology, with APK organoids having reduced viability over time. This study reveals an epithelial-specific role for ATF3 in restricting KRASG12D -mediated PDAC and indicates ATF3 has functions in multiple cell compartments during PDAC progression. Pancreatic epithelial cells from KRASG12D-inducible mice with (Ptf1acreERT/+KRASG12D/+) or without ATF3 (Atf3-/-Ptf1acreERT/+KRASG12D/+; referred to as APK) were isolated 21 days after tamoxifen induced recombination. Gene expression was examined from isolated cells. Isolated cells were also grown in 3D cultures and morphology examined.RNA-seq analysis identified reduced KRAS-signalling in the absence of ATF3, correlating with reduced ADM in APK cultures. Alternatively, we generated mice allowing acinar cell-specific Atf3 deletion at the same time as KRASG12D activation (AacinarPK mice). AacinarPK mice were compared to Ptf1acreERT/+KRASG12D/+ and APK mice two weeks after cerulein-induced pancreatic injury for tissue morphology and gene expression.