Abstract 990: Metastasis suppressor CD82/KAI1 expression is dependent on functional SWI/SNF ARID1A/B
Authors: Rusheeswar Challa, Yutaka Shoji, Kelly A. Conrads, Brian L. Hood, Guisong Wang, Kathleen M. Darcy, Chad A. Hamilton, George Larry Maxwell, Thomas P. Conrads, John I. Risinger
Journal: Cancer Research (2014)

Abstract CD82/KAI1 was one of the first metastasis suppressors identified and is capable of inhibiting the metastatic process in orthotopic tumor models. The expression of the CD82/KAI1 is down-regulated during tumor progression in many tumor types including prostate, breast, lung, bladder, and pancreatic cancers, and this down regulation appears to be at the level of transcription or post-transcription. The gene is not mutated, deleted or silenced by promoter methylation. CD82/KAI1 is also down regulated in advanced gynecologic cancers where CD82/KAI1 loss is associated with the poor overall survival in ovarian cancer. The mechanisms controlling the level of CD82/KAI1 expression remains unclear particularly the widespread loss in advanced cancers. The p53 tumor suppressor (TP53) can directly activate the CD82/KAI1 gene by interacting with the 5-prime upstream region of the CD82/KAI1 gene. Mutant TP53 is unable to bind this promoter site and fails to support CD82/KAI1 transcription. Taken together these data support a direct relationship between TP53 and CD82/KAI1 genes and suggested that the loss of TP53 function, which is common in many types of advanced cancer can lead to downregulation of CD82/KAI1, which then may result in metastases. However many cancers without TP53 mutation also exhibit loss of CD82/KAI1 suggesting that the mechanism for CD82/KAI1 loss is not completely explained by mutant TP53. Furthermore the mutant TP53 state and CD82/KAI1 loss is not strongly correlated in ovarian cancer. In some sarcomas the mechanism of CD82/KAI1 loss is related to the increase of the gp-78 E3 ligase and increased proteasomal degradation. Therefore the regulation of CD82/KAI1 in cells is likely complex. The AT Rich DNA binding protein ARID1A gene is frequently mutated in endometrial and ovarian cancers. In order to explore the functions of ARID1A in these cancers we complemented mutant ARID1A in the ACI-98 endometrial cancer cell line. We utilized a doxycycline inducible system and catalogued the protein changes following ARID1A complementation using LC MS/MS. Among the most differentially expressed proteins was CD82/KAI1. Levels of CD82 were dramatically increased following ARID1A induction. ACI-98 cells were found to be TP53 wild-type and CD82 expression null. QRT-PCR assays confirmed the dramatic increase in CD82/KAI1 mRNA levels and western blots also confirmed restoration of CD82/KAI1 protein following Doxycycline induced ARID1A restoration. We performed ChIP and confirmed that ARID1A was bound to the CD82/KAI1 promoter region close to the TP53 interaction area. Interestingly ACI-98 cells are mutant in both ARID1 homologs A and B. Ectopic expression of ARID1B was also able to restore expression of CD82/KAI1. These data suggest that the SWI/SNFARID1A/B complex is necessary for chromatin remodeling and expression of the CD82/KAI1 gene. Citation Format: Rusheeswar Challa, Yutaka Shoji, Kelly A. Conrads, Brian L. Hood, Guisong Wang, Kathleen M. Darcy, Chad A. Hamilton, George Larry Maxwell, Thomas P. Conrads, John I. Risinger. Metastasis suppressor CD82/KAI1 expression is dependent on functional SWI/SNF ARID1A/B. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 990. doi:10.1158/1538-7445.AM2014-990