Mutation and loss of expression of ARID1A in uterine low-grade endometrioid carcinoma

Abstract

ARID1A is a recently identified tumor suppressor gene that is mutated in approximately 50% of ovarian clear cell and 30% of ovarian endometrioid carcinomas. The mutation is associated with loss of protein expression as assessed by immunohistochemistry. In this study, we evaluated ARID1A immunoreactivity in a wide variety of carcinomas to determine the prevalence of ARID1A inactivation in carcinomas. Mutational analysis of ARID1A was carried out in selected cases. Immunoreactivity was not detected (corresponding to inactivation or mutation of ARID1A) in 36 (3.6%) of 995 tumors. Uterine low-grade endometrioid carcinomas showed a relatively high-frequency loss of ARID1A expression, as 15 (26%) of 58 cases were negative. The other tumor that had a relatively high-frequency loss of ARID1A expression was gastric carcinoma (11%). Mutational analysis showed 10 (40%) of 25 uterine endometrioid carcinomas; none of 12 uterine serous carcinomas and none of 56 ovarian serous and mucinous carcinomas harbored somatic ARID1A mutations. All mutations in endometrioid carcinomas were nonsense or insertion/deletion mutations, and tumors with ARID1A mutations showed complete loss or clonal loss of ARID1A expression. In conclusion, this study is the first large-scale analysis of a wide variety of carcinomas showing that uterine low-grade endometrioid carcinoma is the predominant tumor type harboring ARID1A mutations and frequent loss of ARID1A expression. These findings suggest that the molecular pathogenesis of low-grade uterine endometrioid carcinoma is similar to that of ovarian low-grade endometrioid and clear cell carcinoma, tumors that have previously been shown to have a high-frequency loss of expression and mutation of ARID1A.

Fig. 1

Specificity of the antibody in detecting ARID1A. Western blot analysis shows a predominant protein band with a molecular mass corresponding to ARID1A protein (~280kD) in HeLa cell lysate. Protein expression is significantly decreased in shRNA-2 and shRNA-3 treated HeLa cells compared to control shRNA treated cells (A). Immunohistochemistry using this anti-ARID1A antibody on an ovarian clear cell carcinoma with known bi-allelic somatic insertion/deletion mutations of ARID1A (B). The tumor cells demonstrate undetectable ARID1A immunoreactivity while the stromal cells show intense nuclear staining.

Fig. 2

ARID1A immunoreactivity in representative carcinoma types (right panel) and their normal tissue counterparts (left panel). Negative staining (undetectable level) of ARID1A in a FIGO grade I endometrioid carcinoma (A), an infiltrating ductal carcinoma of the breast (B), a cervical squamous carcinoma (C), and a pancreatic carcinoma (D).

Fig. 3

Pattern of ARID1A immunoreactivity in two uterine endometrioid carcinomas. A. The carcinoma (UEM-5) harbors biallelic ARID1A mutations (nonsense and deletion mutation) and demonstrates a clonal loss of ARID1A expression (asterisk). B. The carcinoma (UEM-3) contains monoallelic nonsense mutation show a clonal loss of ARID1A expression (asterisk). C. The carcinoma with wild-type ARID1A exhibits a diffuse and intense pattern of ARID1A staining. D. The carcinoma with wild-type ARID1A demonstrates diffuse but less intense ARID1A immunoreactivity than the tumor in C. Occasionally, patchy staining can be observed (inset).