ARID1A Maintains Differentiation of Pancreatic Ductal Cells and Inhibits Development of Pancreatic Ductal Adenocarcinoma in Mice

BACKGROUND & AIMS

The ARID1A gene encodes a protein that is part of the large adenosine triphosphate (ATP)-dependent chromatin remodeling complex SWI/SNF and is frequently mutated in human pancreatic ductal adenocarcinomas (PDACs). We investigated the functions of ARID1A during formation of PDACs in mice.

METHODS

We performed studies with Ptf1a-Cre;Kras^G12D mice, which express activated Kras in the pancreas and develop pancreatic intraepithelial neoplasias (PanINs), as well as those with disruption of Aird1a (Ptf1a-Cre;Kras^G12D;Arid1a^f/f mice) or disruption of Brg1 (encodes a catalytic ATPase of the SWI/SNF complex) (Ptf1a-Cre;Kras^G12D; Brg1^f/fmice). Pancreatic ductal cells (PDCs) were isolated from Arid1a^f/f mice and from Arid1a^f/f;SOX9OE mice, which overexpress human SOX9 upon infection with an adenovirus-expressing Cre recombinase. Pancreatic tissues were collected from all mice and analyzed by histology and immunohistochemistry; cells were isolated and grown in 2-dimensional and 3-dimensional cultures. We performed microarray analyses to compare gene expression patterns in intraductal papillary mucinous neoplasms (IPMNs) from the different strains of mice. We obtained 58 samples of IPMNs and 44 samples of PDACs from patients who underwent pancreatectomy in Japan and analyzed them by immunohistochemistry.

RESULTS

Ptf1a-Cre;Kras^G12D mice developed PanINs, whereas Ptf1a-Cre;Kras^G12D;Arid1a^f/f mice developed IPMNs and PDACs; IPMNs originated from PDCs. ARID1A-deficient IPMNs did not express SOX9. ARID1A-deficient PDCs had reduced expression of SOX9 and dedifferentiated in culture. Overexpression of SOX9 in these cells allowed them to differentiate and prevented dilation of ducts. Among mice with pancreatic expression of activated Kras, those with disruption of Arid1a developed fewer PDACs from IPMNs than mice with disruption of Brg1. ARID1A-deficient IPMNs had reduced activity of the mTOR pathway. Human IPMN and PDAC specimens had reduced levels of ARID1A, SOX9, and phosphorylated S6 (a marker of mTOR pathway activation). Levels of ARID1A correlated with levels of SOX9 and phosphorylated S6.

CONCLUSIONS

ARID1A regulates expression of SOX9, activation of the mTOR pathway, and differentiation of PDCs. ARID1A inhibits formation of PDACs from IPMNs in mice with pancreatic expression of activated KRAS and is down-regulated in IPMN and PDAC tissues from patients.

A novel "oxygen-induced" greening process in a cyanobacterial mutant lacking the transcriptional activator ChlR involved in low-oxygen adaptation of tetrapyrrole biosynthesis

ChlR activates the transcription of the chlAII-ho2-hemN operon in response to low-oxygen conditions in the cyanobacterium Synechocystis sp. PCC 6803. Three genes in the operon encode low-oxygen-type enzymes to bypass three oxygen-dependent reactions in tetrapyrrole biosynthesis. A chlR-lacking mutant, ΔchlR, shows poor photoautotrophic growth due to low chlorophyll (Chl) content under low-oxygen conditions, which is caused by no induction of the operon. Here, we characterized the processes of etiolation of ΔchlR cells in low-oxygen conditions and the subsequent regreening of the etiolated cells upon exposure to oxygen, by HPLC, Western blotting, and low-temperature fluorescence spectra. The Chl content of the etiolated ΔchlR cells incubated under low-oxygen conditions for 7 days was only 10% of that of the wild-type with accumulation of almost all intermediates of the magnesium branch of Chl biosynthesis. Both photosystem I (PSI) and photosystem II (PSII) were significantly decreased, accompanied by a preferential decrease of antenna Chl in PSI. Upon exposure to oxygen, the etiolated ΔchlR cells resumed to produce Chl after a short lag (∼2 h), and the level at 72 h was 80% of that of the wild-type. During this novel "oxygen-induced" greening process, the PSI and PSII contents were largely increased in parallel with the increase in Chl contents. After 72 h, the PSI content reached ∼50% of the wild-type level in contrast to the full recovery of PSII. ΔchlR provides a promising alternative system to investigate the biogenesis of PSI and PSII.