Endocrine Abstracts

AT-rich interacting domain (ARID) subunits can interact with the glucocorticoid receptor (GR) and therefore may be essential for gene transcription dependent on receptor signalling. Glucocorticoids are steroid hormones important for regulating a variety of physiological processes through the binding and activation of GR. GR associates with numerous co-regulators, such as chromatin remodelling factors, to mediate gene induction or repression. One chromatin remodelling complex which interacts with GR is the ATPase driven SWItch/Sucrose NonFermentable (SWI/SNF) complex. ARID1a is an essential subunit of the SWI/SNF complex thought to be responsible for interacting with GR and recruitment of the complex to DNA. ARID1a mutations have been discovered in a wide range of human carcinomas including ovarian, uterine, liver, lung, breast, pancreatic, renal and colon cancers. A subset of GR dependent genes require the SWI/SNF remodelling complex for regulation, therefore absence of the functional ARID1a protein may impair GR signalling pathways. We hypothesise that inactivating ARID mutations could interfere with GR dependent gene regulation potentially through disrupting GR binding to target sequences. We have used two human cell lines, HeLa cells which possess the endogenous ARID1a and SKOV3 cells which contain an inactivating ARID1a mutation, to assess the impact of the absence of the functional ARID1a on GR dependent transcription. Using chromatin immunoprecipitation (ChIP) assays in the SKOV3 cells compared to HeLa cells, we show a lack of GR binding at the Per1 binding site known to require chromatin remodelling. We further demonstrate a delay in the transcriptional induction of GR dependent genes, including Per1, in response to dexamethasone treatment in the SKOV3 cells in comparison to HeLa cells. The findings from this study strongly implicate ARID1A in regulating temporal dynamics of GR transcriptional dynamics, and this is being further assessed by gene knockdown and functional interference studies.