Association of ARID1A deficiency with invasive transformation in metastatic bladder cancer.

Abstract

656 Background: ARID1A is an essential component of the BAF complex, a large SWI/SNF chromatin-remodeling complex which is implicated in bladder cancer (BC) pathogenesis. While ARID1A mutations are more highly represented in metastatic rather than localized tumors, the biological consequences of ARID1A loss in BC remain to be elucidated. We hypothesize that ARID1A deficiency primes an invasive transformation in BC, thus increasing the likelihood of disease progression and metastases. We used CRISPR/Cas9-mediated gene editing to knockout (KO) the ARID1A gene in several BC cell lines, thus providing a platform for cellular function assays. We show that ARIDA1 loss potentiates an invasive phenotype in these cell lines, giving evidence for its transformative role in the development of higher stage and metastatic BC. Methods: A CRISPR-Cas9 KO was performed with three cell lines with wild-type (WT) ARID1A (T24, SW1710, and 5637). This was accomplished by developing sgRNAs against ARID1A with a GFP marker and carrying out single-cell fluorescence-activated cell sorting (FACS) following nucleofection to identify ARID1A-deficient clones. Western blot analysis was performed on the resulting clones to confirm complete loss of ARID1A. Baseline proliferation studies were performed on the KO and WT cell lines. Finally, invasion studies were performed on the KO and WT cells with a scratch assay. Results: CRISPR-Cas9 directed KO of ARID1A yielded ARID1A-deficient clones for SW1710, T24, and 5637. The proliferation rates for each cell line were analyzed and compared which showed no significant differences. A scratch assay was performed with the cell lines in triplicate, with each ARID1A-deficient cell line showing a trend towards more rapid wound closure than its matched WT cell line (WT=31.5% vs. KO=53.5% for SW1710, p=0.15; WT=17.2% vs. KO=52.0% for T24, p=0.07; WT=10.4% vs. KO=13.9% for 5637, p=0.59). Conclusions: To explore the increased frequency of ARID1A alterations in metastatic BC compared to non-invasive tumors, we developed a model of ARID1A-deficient BC using CRISPR-Cas9. We compared the relative invasiveness of the lines using a scratch assay. All lines trended towards a more invasive phenotype following ARID1A KO, which was especially pronounced in T24. Taken together, these data suggest that ARID1A deficiency in BC may prime tumors for a more invasive phenotype, which may help to explain the higher frequency of ARID1A alterations in higher stage and metastatic samples.