Frequent somatic mutations of the telomerase reverse transcriptase promoter in ovarian clear cell carcinoma but not in other major types of gynaecological malignancy

Abstract

Up-regulated expression of telomerase reverse transcriptase (TERT) and subsequent maintenance of telomere length are essential in tumour development. Recent studies have implicated somatic gain-of-function mutations at the TERT promoter as one of the mechanisms that promote transcriptional activation of TERT; however, it remains unclear whether this genetic abnormality is prevalent in gynaecological neoplasms. We performed mutational analysis in a total of 525 gynaecological cancers, and correlated TERT promoter mutations with clinicopathological features. With the exception of ovarian clear cell carcinomas, in which mutations were found in 37 (15.9%) of 233 cases, the majority of gynaecological malignancies were wild-type. TERT promoter mutation does not appear to be an early event during oncogenesis, as it was not detected in the contiguous endometriosis associated with ovarian clear cell carcinoma. Ovarian clear cell carcinoma cell lines with TERT promoter mutations exhibited higher TERT mRNA expression than those with wild-type sequences (p = 0.0238). TERT promoter mutation tended to be mutually exclusive with loss of ARID1A protein expression (p = 4.4 × 10(-9) ) and PIK3CA mutation (p = 0.0019) in ovarian clear cell carcinomas. No associations with disease-specific survival were observed for ovarian clear cell carcinoma. The above results, in conjunction with our previous report showing longer telomeres in ovarian clear cell carcinomas relative to other types of ovarian cancer, suggests that aberrations in telomere biology may play an important role in the pathogenesis of ovarian clear cell carcinoma.

Keywords: ARID1A; PIK3CA; TERT promoter; clear cell carcinoma; telomerase; telomere.

Fig. 1

(a) TERT promoter mutations in ovarian clear cell carcinoma. Shown are representative chromatograms of the wild-type TERT promoter and two mutated TERT promoters at two different hot spots. Both mutations create an identical 11bp sequence: CCCCTTCCGGG. (b) An example of ovarian clear cell carcinoma arising from an endometriotic cyst. TERT promoter mutation occurred in clear cell carcinoma but not in the adjacent endometriotic cyst epithelium. (c) Ovarian clear cell carcinoma cell lines with mutated TERT promoter have increased expression of TERT mRNA. Red circles: OV207 and JHOC5 cells with c.−124C>T mutation; blue circle: ES-2 cell with c.[−139C>T;−138C>T] tandem mutation; black horizontal bar: mean; error bar: SEM. (d) Comparison of telomere length between ovarian clear cell carcinomas with and without TERT promoter mutation. Black horizontal bar: mean; error bar: SEM; gray horizontal bar: cutoff for binary analysis.

Fig. 2

(a) Correlation between TERT promoter mutation and ARID1A immunoreactivity in ovarian clear cell carcinomas. (b) Correlation between TERT promoter mutation and PIK3CA mutation in ovarian clear cell carcinomas. (c) Mutation status of TERT promoter and PIK3CA, and immunostaining result of ARID1A in 71 clear cell carcinoma tissues. Blue: TERT promoter mutation; orange: loss of ARID1A expression; green: PIK3CA mutation.

Fig. 3

Kaplan-Meier survival curves of ovarian clear cell carcinoma patients. Overall survival time of patients with TERT promoter mutation is similar to patients with wild-type sequence.