CRISPR/Cas9-Mediated Gene Knockout of ARID1A Promotes Primary Progesterone Resistance by Downregulating Progesterone Receptor B in Endometrial Cancer Cells

Medroxyprogesterone (MPA) is used for the conservative treatment of endometrial cancer. Unfortunately, progesterone resistance seriously affects its therapeutic effect. The purpose of the current study was to investigate the influence of deletion of AT-rich interactive domain 1A (ARID1A) in progesterone resistance in Ishikawa cells. Ablation of ARID1A was conducted through the CRISPR/Cas9 technology. Acquired progesterone-resistant Ishikawa (Ishikawa-PR) cells were generated by chronic exposure of Ishikawa cells to MPA. The sensitivity of the parental Ishikawa, Ishikawa-PR, and ARID1A-deficient cells to MPA and/or LY294002 was determined using the Cell Counting Kit-8 (CCK-8) assay and flow cytometry analysis. In addition, Western blot analysis and reverse transcription-polymerase chain reaction was performed to evaluate the mRNA and protein expression levels of ARID1A, progesterone receptor B (PRB), and P-AKT. Both Ishikawa-PR and ARID1A knockout cells showed insensitivity to MPA, downregulation of PRB, and hyperphosphorylation of AKT compared to the parental Ishikawa cells. Pretreatment with LY294002 significantly enhanced the ability of MPA to suppress proliferation and to induce apoptosis in the parental and Ishikawa-PR cells via the inhibition of AKT activation and upregulation of PRB transcriptional activity. However, the PRB transcriptional activity and insensitivity to MPA were irreversible by LY294002 in ARID1A-deficient cells. Ablation of ARID1A is associated with low PRB expression, which serves an important role in primary progesterone resistance. Akt inhibition cannot rescue PRB or sensitize to MPA in ARID1A knockout cells. These findings suggest that ARID1A may act as a reliable biomarker to predict the response for the combination of AKT inhibitor and MPA treatment.