S. C. Wang1,2, X. Sun2, I. Nassour1,2, X. Luo2, J. Chuang2, L. Li2, T. Maples2, C. Celen2, L. H. Nguyen2,3, S. Zhang2, H. Zhu2 1University Of Texas Southwestern Medical Center,Division Of Surgical Oncology,Dallas, TX, USA 2University Of Texas Southwestern Medical Center,Children’s Research Institute,Dallas, TX, USA 3Howard Hughes Medical Institute,Chevy Chase, MD, USA
Introduction:
ARID1A, a component in the SWI/SNF chromatin-remodeling complex, is one of the most commonly mutated genes in cancer. Because a majority of the mutations are loss-of-function, ARID1A is widely assumed to be a tumor suppressor. However, the functional effect of ARID1A loss is unclear. Here, we used a genetically engineered mouse model to dissect the effects of Arid1a loss in liver cancer.
Methods:
A liver-specific Tet-Off MYC overexpression liver cancer model was used. The tetracycline transactivator was driven by the liver activator protein promoter and MYC expression was under the control of the tetracycline response element (LAP-tTA; TRE-MYC, referred heretofore as LAP-MYC mice). MYC was induced at birth by removal of doxycycline. Liver specific Arid1a knockout (LKO) was achieved by crossing in Albumin-Cre; Arid1af/f . A lentiviral system was used to stably express shArid1a in the mouse hepatoma Hepa1c1c7 cell line. The Arid1a overexpression construct was delivered with adenovirus.
Results:
LAP-MYC LKO mice had significantly improved survival as compared to LAP-MYC mice (Figure A; HR: 0.45; 95% CI: 0.28 to 0.80, P < 0.01) suggesting that Arid1a had oncogenic properties. When we overexpressed Arid1a in LAP-MYC mice, we found increased tumor burden, confirming that Arid1a could be oncogenic (Figure B; P < 0.01). Next, we transplanted Hepa1c1c7 cell lines that stably expressed shArid1a in the subcutaneous tissue of immunocompromised mice. The tumors grew at the same rate as cells that had normal Arid1a expression. These data suggest that Arid1a was required for normal initiation of liver cancer but did not constrain the growth of established cancer cells.
RNA-seq of LAP-MYC and LAP-MYC LKO tumors demonstrated pro-invasion and metastasis gene programs were upregulated in the LAP-MYC LKO tumors, signifying that in this context, Arid1a had tumor suppressive effects. To test the functional metastatic effects of Arid1a loss, we delivered the shArid1a expressing Hepa1c1c7 cells systemically via tail vein injections and found that the Arid1a knockdown cells resulted in more lung metastases than control cells (Figure C; P < 0.001). This showed that in established cancers Arid1a was tumor suppressive and its loss conferred increased metastatic potential.
Conclusions:
Arid1a in liver cancer has both oncogenic and tumor suppressive properties dependent on temporal context. It potentiates tumor initiation and constrains metastases. Other contexts, such as tissue type and dosage, should also be explored to fully characterize the role that Arid1a plays in cancer.
