Arid1a restrains Kras-dependent changes in acinar cell identity

Mutations in members of the SWI/SNF chromatin remodeling family are common events in human cancer, but the mechanisms whereby disruption of SWI/SNF components alters tumorigenesis remain poorly understood. To model the effect of loss of function mutations in the SWI/SNF subunit Arid1a in pancreatic ductal adenocarcinoma (PDAC) initiation, we directed shRNA triggered, inducible and reversible suppression of Arid1a to the pancreas of mice in the setting of oncogenic KrasG12D. Arid1a cooperates with Kras in the adult pancreas as postnatal silencing of Arid1a following sustained KrasG12D expression induces rapid and irreversible reprogramming of acinar cells into mucinous PDAC precursor lesions. In contrast, Arid1a silencing during embryogenesis, concurrent with KrasG12D activation, leads to retention of acinar cell fate. Together, our results demonstrate Arid1a as a critical modulator of Kras-dependent changes in acinar cell identity, and underscore an unanticipated influence of timing and genetic context on the effects of SWI/SNF complex alterations in epithelial tumorigenesis. Identification of the transcritpional changes induced upon dox-inducible Arid1a knockdown in mutant Kras pancreatic epithelial cells: Arid1a-downregulated vs Arid1a-expressing mutant Kras-pancreatic epithelial cells were FACS-sorted from pancreata from p48Cre;RIK;LSL-KrasG12;TRE-shRNA mice (harbouring Arid1a shRNAs -6421 or 1803- or control Renilla shRNA -713-) at day 5 post- doxycycline treatment. Mice were placed on doxycycline diet at 5 weeks of age to induce expression of the indicated shRNAs. 3 biological replicates (independent mice) were used per shRNA condition (713, 6421, 1803).

SWI/SNF染色质重塑家族（SWI/SNF chromatin remodeling family）成员的突变在人类癌症中极为常见，但SWI/SNF组分失调驱动肿瘤发生的具体机制仍未得到充分阐明。为模拟SWI/SNF亚基Arid1a功能丧失突变对胰腺导管腺癌（pancreatic ductal adenocarcinoma, PDAC）发生的影响，我们在致癌性KRASG12D背景下，通过短发卡RNA（short hairpin RNA, shRNA）介导的可诱导且可逆的Arid1a沉默，靶向作用于小鼠胰腺组织。成年小鼠胰腺中，Arid1a与KRAS存在协同效应：在持续表达KRASG12D后对Arid1a进行出生后沉默，可快速且不可逆地将腺泡细胞重编程为黏液性PDAC前体病变。与之相反，胚胎发生期伴随KRASG12D激活的Arid1a沉默，则会保留腺泡细胞的细胞命运。综上，本研究结果证实Arid1a是调控KRAS依赖的腺泡细胞身份改变的关键调节因子，并突显了时序与遗传背景对SWI/SNF复合物失调在上皮肿瘤发生中作用的未预期影响。本数据集旨在鉴定突变KRAS胰腺上皮细胞中多西环素（doxycycline, dox）诱导的Arid1a敲低所引发的转录组变化：将携带Arid1a shRNA（-6421或1803）或对照海肾shRNA（Renilla shRNA，-713）的p48Cre;RIK;LSL-KrasG12;TRE-shRNA小鼠，在多西环素处理后第5天摘取胰腺组织，通过荧光激活细胞分选（fluorescence-activated cell sorting, FACS）分离得到Arid1a低表达与Arid1a正常表达的突变KRAS胰腺上皮细胞。小鼠于5周龄时喂食多西环素饲料以诱导指定shRNA的表达。每个shRNA处理组（713、6421、1803）均使用3个生物学重复（即独立小鼠样本）。