Abstract 2733: Novel function of the RAI2 protein in genomic integrity of breast cancer cells

Abstract

Abstract We have recently identified the RAI2 protein as putative metastasis-suppressor related to dedifferentiation, early occurring bone metastasis formation, and survival of hormone dependent breast carcinomas. Nevertheless, low RAI2 expression is also predictive for poor patient outcome in hormone independent tumors and is furthermore associated with mutation of p53 in primary breast tumors. Thus, besides sustaining luminal differentiation, RAI2 might possess a general function as tumor suppressor that is, as indicated by association with p53 status, possibly related to maintenance of genomic stability. In order to characterize its potential role in genomic integrity, we screened lysates from RAI2 depleted MCF-7 and KPL-1 breast cancer cell lines with phosphorylation-specific antibody arrays. Additionally, we analyzed changes in expression of cell cycle related genes and proteins by qPCR and Western Blot analysis. We also conducted cytogenetic assays to investigate whether RAI2 depletion affects chromosomal stability and mitotic progression. Finally, we evaluated a possible association of RAI2 expression with aneuploidy in published expression data sets from breast cancer patients. As revealed by antibody array analysis, RAI2 depletion causes activation of p53 protein in MCF-7 and KPL-1 breast cancer cells, which was accompanied by a significant increase of senescent cells in the corresponding cell populations. Furthermore RAI2 depletion causes downregulation of several key factors of G2/M transition, like Aurora kinases A and B as well as Cyclins A2, B1 and B2. Concomitantly, we found in RAI2-depleted cell cultures reduction of mitotic index, increase of unattached chromosomes in metaphase and lagging chromosomes and during anaphase. This finding was further approved by an increase of numerical aberrations in RAI2 knockdown cells. Finally, we could show an association between low RAI2 expression and higher level of chromosomal instability in primary tumors from breast cancer patients. In conclusion, we found that loss of RAI2 function is associated with decreased mitotic fidelity. Thus, besides sustaining differentiation in hormone dependent breast tumor, RAI2 also acts as general tumor suppressor that maintains genomic integrity. Reference: Werner S et al., Cancer Discovery. 2015 May;5(5):506-19 Citation Format: Stefan Werner, Kerstin Borgmann, Klaus Pantel, Harriet Wikman. Novel function of the RAI2 protein in genomic integrity of breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2733.