Breast cancer, the most common malignancy among women, is closely associated with mutations in the tumor suppressor gene BRCA. DSS1, a component of the TRanscription–EXport-2 (TREX-2) complex involved in transcription and mRNA nuclear export, stabilizes BRCA2 expression. DSS1 is also related to poor prognosis in patients with breast cancer owing to the induction of chemoresistance. Recently, BRCA2 was shown to be associated with the TREX-2 component PCID2, which prevents DNA:RNA hybrid R-loop formation and transcription-coupled DNA damage. This study aimed to elucidate the involvement of these TREX-2 components and BRCA2 in the chemosensitivity of breast carcinomas. Our results showed that compared with that in normal breast tissues, DSS1 expression was upregulated in human breast carcinoma, whereas PCID2 expression was comparable between normal and malignant tissues. We then compared patient survival time among groups divided by high or low expressions of DSS1, BRCA2, and PCID2. Increased DSS1 expression was significantly correlated with poor prognosis in recurrence-free survival time, whereas no differences were detected in the high and low BRCA2 and PCID2 expression groups. We performed in vitro analyses, including propidium iodide nuclear staining, single-cell gel electrophoresis, and clonogenic survival assays, using breast carcinoma cell lines. The results confirmed that DSS1 depletion significantly increased chemosensitivity, whereas overexpression conferred chemoresistance to breast cancer cell lines; however, BRCA2 expression did not affect chemosensitivity. Similar to DSS1, PCID2 expression was also inversely correlated with chemosensitivity. These results strongly suggest that DSS1 and PCID2 depletion is closely associated with increased chemosensitivity via BRCA2-independent DNA damage. Together with the finding that DSS1 is not highly expressed in normal breast tissues, these results demonstrate that DSS1 depletion confers a druggable trait and may contribute to the development of novel chemotherapeutic strategies to treat DSS1-depleted breast carcinomas independent of BRCA2 mutations.
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All data collected and analyzed in this study are available from the corresponding author, KK, upon reasonable request. Some data are publicly available in the Kaplan–Meier plotter database at https://kmplot.com/analysis/.
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We thank Ms. Rie Miura for the technical assistance.
This work was supported by a Grant-in-Aid for challenging Exploratory Research 16K15603 (NG), a Grant-in-Aid for Young Scientists 20K16228 (YS), and Grants-in-Aid for Scientific Research (C) 24590388, 15K10083, and 20K07686 (KK) from the Japan Society for the Promotion of Science; a Grant-in-Aid for Young Scientists from Fujita Health University (YS); and Grants-in-Aid from Aichi Cancer Research Foundation (KK), the 24th General Assembly of the Japanese Association of Medical Sciences (KK), and Aichi Health Promotion Foundation (KK). AR was supported by an Indonesian Directorate General of Higher Education (DIKTI) Scholarship.
Conflict of interest
The authors declare no competing interests.
Ethics approval and consent to participate
The collection of human tissue samples was approved by the Ethics Committee of Nagoya City University Graduate School of Medical Sciences and Fujita Health University. Sample collection was performed in strict accordance with the approved guidelines. All participants signed informed consent documents.
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Gondo, N., Sakai, Y., Zhang, Z. et al. Increased chemosensitivity via BRCA2-independent DNA damage in DSS1- and PCID2-depleted breast carcinomas. Lab Invest (2021). https://doi.org/10.1038/s41374-021-00613-6