Abstract A47: The acinar differentiation factor PTF1A negatively regulates EGFR-mediated acinar cell reprogramming
Authors: Narayanan Shuba M. , Krah Nathan M. , Murtaugh L. Charles 
Published: December 2016

The primary goal of this study is to characterize interactions between the master acinar transcription factor, Ptf1a, and signal transduction pathways implicated in acinar reprogramming.

Animal models suggest that acinar-ductal metaplasia (ADM) is one of the first steps in the initiation of pancreatic cancer. It is now established that acinar-specific activation of the Kras oncogene is sufficient at the whole-organ level to cause ADM and PanIN formation in mice, although it does so only inefficiently at the level of individual cells. Recently, our lab demonstrated that deletion of the master acinar transcriptional regulator, Ptf1a, facilitates ADM. Additionally, loss of Ptf1a dramatically accelerates PanIN formation when compounded with an oncogenic Kras mutation. Mechanistically, loss of Ptf1a activates transcriptional signatures of several signaling pathways that have been implicated in promoting acinar to ductal metaplasia (ADM) as well as PDAC progression. Prime among these candidate pathways is epidermal growth factor receptor (EGFR) signaling, which promotes acinar to ductal metaplasia (ADM) via the Ras-Raf-MEK-ERK pathway. In this study we test whether Ptf1a negatively regulates EGFR signaling to restrain acinar reprogramming and acinar-to-ductal metaplasia.

To test this hypothesis, we performed in vitro culture assays on acinar clusters isolated from mice containing activated oncogenic KRAS alone (KrasG12D) or KrasG12D-Ptf1a cKO double mutant mice. We find that acinar clusters from KrasG12D-Ptf1a cKO double mutant mice undergo reprogramming, giving rise to duct-like cysts, both more rapidly and at a greater frequency than KrasG12D mice. In congruence with previous work, stimulation with the EGFR ligand, TGFα, increases the size and frequency of cyst formation in both KrasG12D and KrasG12D-Ptf1a cKO mice, suggesting that EGFR activation increases the transforming ability of oncogenic KRAS. Consistent with previous studies, blocking EGFR signaling using the pharmacological inhibitor Erlotinib, prevented ADM in acinar clusters from mice expressing oncogenic KRAS alone. Surprisingly, however, Erlotinib does not prevent ADM and cyst formation in KrasG12D-Ptf1a cKO mice, suggesting that acinar differentiation programs are required for the inhibitory effects of this drug. These results additionally indicate that EGFR is dispensable for ADM when Ptf1a is deleted. On the other hand, restriction of downstream signaling using the MEK inhibitor PD-0325901 inhibits reprogramming in acinar clusters, despite deletion of Ptf1a in KrasG12D mice. Since Ptf1a is downregulated in both mouse and human PDAC, these results highlight the potential of MEK inhibitors as feasible therapeutics, and the possibility that varying differentiation competence of tumor cells underlies the variable clinical effectiveness of Erlotinib and other EGFR inhibitors.

Going forward, we will investigate whether reintroducing Ptf1a into dedifferentiated cells is sufficient to reprogram them back to an acinar-like phenotype. Using in vitro culture, we will determine if cells re-differentiate and regain sensitivity to Erlotinib with ectopic expression of Ptf1a. We will also characterize target genes of Ptf1a whose dysregulation leads to EGFR independence. Ultimately, these studies will lead us to investigate if reactivation of Ptf1a expression could represent a novel therapeutic avenue for PDAC.

Citation Format: Shuba M. Narayanan, Nathan M. Krah, L. Charles Murtaugh.{Authors}. The acinar differentiation factor PTF1A negatively regulates EGFR-mediated acinar cell reprogramming. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A47.