Characterizing the Discordance between AT-Rich Interacting Domain 1A Protein and Genotype in Endometrioid-Type Endometrial Tumors.

ARID1A is one of the most frequently mutated genes in endometrial cancer, with approximately 40% of patients harboring an ARID1A mutation. However, relatively little is known about how AT-rich interacting domain 1A (ARID1A) protein loss shapes endometrial cancer pathogenesis. Mounting evidence from other malignancies suggests that ARID1A protein can be regulated post-translationally, independent of genotype. However, most studies in endometrial cancer evaluate genotype alone, overlooking the potential for alternative mechanisms of ARID1A loss. To address this gap, ARID1A protein expression and genotype were examined in endometrioid tumors, and associated transcriptional changes were characterized. Evaluation of ARID1A protein in 71 human endometrioid tumors demonstrates that protein loss can occur regardless of ARID1A genotype. Retention or deficiency of ARID1A protein was not significantly related to variant allele frequency or location of mutation in human tumors with mutant ARID1A. A human endometrial cancer cell model suggests that ARID1A protein loss can occur through proteasomal degradation. Furthermore, ARID1A protein expression was found to be a predictor of worse overall survival in The Cancer Genome Atlas cohort of ARID1A wild-type endometrioid tumors. Spatial transcriptomics of 16 human endometrioid tumors revealed that both genotype and protein expression of ARID1A play a role in shaping unique transcriptional signatures in endometrial cancer and can be used to predict patient prognosis. Suggesting evaluation of ARID1A should not be done solely by sequencing techniques.