ARID1A is a tumor suppressor gene that belongs to the switch/sucrose non-fermentable chromatin remodeling gene family. It is mutated in many types of human cancer with the highest frequency in endometrium-related ovarian and uterine neoplasms including ovarian clear cell, ovarian endometrioid, and uterine endometrioid carcinomas. We have previously reported that mutations in the promoter of human telomerase reverse transcriptase (TERT) rarely co-occur with the loss of ARID1A protein expression, suggesting a potential role of ARID1A in telomere biology. In this study, we demonstrate that ARID1A negatively regulates TERT transcriptional regulation and activity via binding to the regulatory element of TERT and promotes a repressive histone mode. Induction of ARID1A expression was associated with increased occupancy of SIN3A and H3K9me3, known transcription repressor and histone repressor marks, respectively. Thus, loss of ARID1A protein expression caused by inactivating mutations reactivates TERT transcriptional activity and confers a survival advantage of tumor cells by maintaining their telomeres.
ARID1A3 encodes BAF250 (also known as p270), which interacts with the ATPase subunit, BRG1 or BRM, and a set of core subunits (BAF47, BAF155, and BAF170) to form the switch/sucrose non-fermentable (SWI/SNF) chromatin remodeling complex. By utilizing the energy from ATP hydrolysis, these complexes rearrange the distribution of nucleosomes, thereby modifying chromatin configuration and DNA accessibility to cellular machineries involved in transcription, DNA replication, DNA methylation, and DNA repair (1-3).The discovery of molecular genetic aberrations in chromatin remodelers converged genetic and epigenetic dysregulation, which contributes to the development and progression of numerous diseases, including cancer. Somatic ARID1A mutations were first discovered in ovarian clear cell carcinoma (4, 5) and subsequently reported in endometrium-derived carcinomas and several other cancer types (6, 7). Mutations of ARID1A occur throughout the entire coding sequence, mostly frameshift and nonsense mutations, thereby resulting in a loss of ARID1A protein expression. Hence, ARID1A is implicated as a tumor suppressor, and indeed, functional studies have demonstrated that ARID1A loss can promote tumorigenesis by affecting proliferation, differentiation, and apoptosis (8 -10). At the molecular level, our previous study demonstrated that the ARID1A complex interacted and collaborated with p53 to regulate transcription of several effectors including CDKN1A encoding p21 (8). In genetically engineered mice, whereas Arid1a deletion by itself is insufficient to transform cells, codeletion of Arid1a with either Pten or Pik3ca is required to drive the formation of ovarian endometrioid and clear cell-like carcinomas, respectively (11, 12).To further elucidate molecular mechanisms of ARID1A in preventing tumorigenesis, we sought to identify additional molecular genetic alterations that tend to be absent in ARID1A mutated tumors. The nature of ...