Abstract 5219: Characterization of the breast cancer resistance protein BCRP in clear cell renal cell carcinoma
Authors: Fisel Pascale , Reustle Anna , Renner Olga , Büttner Florian , Winter Stefan , Kruck Stephan , Rausch Steffen , Nies Anne T. , Hennenlotter Jörg , Scharpf Marcus , Fend Falko , Stenzl Arnulf , Bedke Jens , Schwab Matthias , Schaeffeler Elke 
Published: July 2017

Abstract
Introduction: The breast cancer resistance protein BCRP, encoded by ABCG2, is a member of the ABC transporter family and is well-known for its contribution to multi-drug resistance in cancer. Although BCRP expression is altered in various cancer types, its role and function in cancer, independent from drug efflux, remains largely elusive. In this study, we aimed to elucidate regulatory mechanisms of ABCG2 expression and its biological relevance in clear cell renal cell carcinoma (ccRCC) as well as associations with response to sunitinib treatment in patients with metastatic ccRCC.
Experimental Procedures: Data from the ccRCC cohort of The Cancer Genome Atlas (TCGA) was used to assess ABCG2 mRNA expression (n=463), DNA methylation (n=288) and genetic variants present in tumor tissue (n=326) within the ABCG2 gene region. An independent ccRCC cohort of 64 patients was used for the analysis of ABCG2 mRNA and protein expression by TaqMan quantitative real time PCR or immunohistochemical staining of TMAs, respectively, and for genotyping of 34 variants in the ABCG2 gene by MALDI-TOF mass spectrometry. The influence of miRNAs on ABCG2 expression was investigated in the second cohort and validated in in vitro cell culture experiments performed in the renal cancer cell line A498 to confirm the interaction of selected miRNAs with the ABCG2 3’UTR. ABCG2 mRNA data and treatment information of a third ccRCC cohort was used to elucidate potential links of ABCG2 with sunitinib response.
Results: In the TCGA cohort low ABCG2 mRNA expression was significantly associated with clinicopathological features (T: P=4.79e-11, N: P=9.76e-04, M: P=1.28e-06, G: P=6.61e-15 and tumor necrosis: P=9.76e-04) and with inferior patient survival (HR=0.22; 95%CI: 0.15-0.32; P[logrank]&lt;10e-14). DNA methylation levels within the ABCG2 gene were low and hardly variable in ccRCC patients. Somatic variants were only found in a minority of patients and together with genetic variants had only a moderate influence on ABCG2 expression and patient survival. The link between ABCG2 expression with survival could be confirmed in the second ccRCC cohort. The investigated variants did not significantly affect ABCG2 expression on mRNA or protein level. miR-212-3p and miR-132-3p were identified to be linked to ABCG2 protein expression in ccRCC patients of the second cohort. The interaction of these miRNAs with the ABCG2 3’UTR was confirmed in in vitro cell culture experiments by reporter gene assays. Analysis of a potential association of ABCG2 expression with sunitinib response revealed a better outcome for patients with high ABCG2 levels.
Conclusion: In this study, we found that higher ABCG2 expression contributes to longer survival in ccRCC patients and better response to sunitinib treatment. Whereas genetic variants had only a minor impact on ABCG2 variability in ccRCC, epigenetic regulation by miRNAs, in particular miR-212-3p and miR-132-3p, contributed to aberrant ABCG2 expression.
Citation Format: Pascale Fisel, Anna Reustle, Olga Renner, Florian Büttner, Stefan Winter, Stephan Kruck, Steffen Rausch, Anne T. Nies, Jörg Hennenlotter, Marcus Scharpf, Falko Fend, Arnulf Stenzl, Jens Bedke, Matthias Schwab, Elke Schaeffeler. Characterization of the breast cancer resistance protein BCRP in clear cell renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5219. doi:10.1158/1538-7445.AM2017-5219