Maintenance of acinar cell organization is critical to preventing Kras-induced acinar-ductal metaplasia

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers owing to a number of characteristics including difficulty in establishing early diagnosis and the absence of effective therapeutic regimens. A large number of genetic alterations have been ascribed to PDAC with mutations in the KRAS2 proto-oncogene thought to be an early event in the progression of disease. Recent lineage-tracing studies have shown that acinar cells expressing mutant KrasG12D are induced to transdifferentiate, generating duct-like cells through a process known as acinar-ductal metaplasia (ADM). ADM lesions then convert to precancerous pancreatic intraepithelial neoplasia (PanIN) that progresses to PDAC over time. Thus, understanding the earliest events involved in ADM/PanIN formation would provide much needed information on the molecular pathways that are instrumental in initiating this disease. Since studying the transition of acinar cells to metaplastic ductal cells in vivo is complicated by analysis of the entire organ, an in vitro 3D culture system was employed to model ADM outside the animal. KrasG12D-expressing acinar cells rapidly underwent ADM in 3D culture, forming ductal cysts that silenced acinar genes and activated duct genes, characteristics associated with in vivo ADM/PanIN lesions. Analysis of downstream KRAS signaling events established a critical importance for the Raf/MEK/ERK pathway in ADM induction. Additionally, forced expression of the acinar-restricted transcription factor Mist1, which is critical to acinar cell organization, significantly attenuated KrasG12D-induced ADM/PanIN formation. These results suggest that maintaining MIST1 activity in KrasG12D-expressing acinar cells can partially mitigate the transformation activity of oncogenic KRAS. Future therapeutics that target both the MAPK pathway and Mist1 transcriptional networks may show promising efficacy in combating this deadly disease.

GRP78 haploinsufficiency suppresses acinar-to-ductal metaplasia, signaling, and mutant Kras -driven pancreatic tumorigenesis in mice

“…GRP78 has been shown to costain with p-AKT in PDAC (26); thus, similar mechanisms may apply. ERK activation is also critical for ADM induction and PDAC development formation, and ERK inhibitor blocks TGFα-induced ADM (33,49). Silencing GRP78 in hepatocellular carcinoma cells and glioblastoma cells reduced ERK activation, suggesting a causative effect (50,51).…”

RAB26 coordinates lysosome traffic and mitochondrial localization

“…Loss of MIST1 results in increased susceptibility to pancreatitis (Alahari et al, 2011;Kowalik et al, 2007;Zhu et al, 2004), and, in wild-type mice, pancreatitis leads to silencing of Mist1 (Shi et al, 2013;Shi et al, 2009). Acute pancreatitis is caused by inappropriate interaction between lysosomal enzymes and zymogen constituents of secretory granules (Gaiser et al, 2011;Halangk et al, 2000;Saluja et al, 1997), which leads to mitochondrial disorganization (Mareninova et al, 2006;Odinokova et al, 2009).…”

IER3 supports KRASG12D-dependent pancreatic cancer development by sustaining ERK1/2 phosphorylation

“…However, since IER3 is a multifunctional factor, additional work is required to define whether this protein exerts additional protumoral effects through interference with other signaling pathways, in particular NF-κB (10,48) and PI3K/AKT (17). Similarly, with respect to cellular mechanisms, it is possible that this protein additionally modulates pancreatic carcinogenesis by modifying immunological responses (49,50) and apoptosis (10,11,28,51), which are well-characterized players in the process of pancreatic cell transformation. Thus, our present findings not only extend the existing knowledge in the field, but also generate the rational for additional studies.…”

“…Primary cultures of acini from LSL-Kras G12D ;Ier3 +/+ or LSL-Kras G12D ;Ier3 -/-animals was performed as previously described (49). Briefly, mouse pancreas was immediately removed after euthanasia, cut into small pieces, and digested with 200 μg/ml collagenase P (Sigma-Aldrich) for 20 minutes at 37°C.…”