Abstract 2372: The metastasis efficiency modifier ribosomal RNA processing 1 homologue (RRP1B) is a chromatin-associated factor

Abstract

Abstract Previous experiments using the polyoma middle T (PyMT) mouse model of mammary tumorigenesis have demonstrated that host germline variation modulates metastasis in breast cancer. Recent work using the PyMT model has identified novel metastasis susceptibility genes, an example of which includes Rrp1b (ribosomal RNA processing 1 homolog B). Over-expression of Rrp1b in a mouse mammary tumor cell line induces a gene expression signature that predicts survival in a well characterized Dutch breast cancer dataset. Additionally, a polymorphism was identified within human RRP1B (G1421A; P436L), which is associated with differential survival in multiple breast cancer cohorts. Here we extend the analysis of RRP1B function by demonstrating that the Rrp1b activation gene expression signature accurately predicts survival in three additional publicly available breast carcinoma gene expression datasets. We have also investigated the mechanism of action of RRP1B by defining protein binding partners for this germline-encoded metastasis modifier. Tandem affinity purification demonstrated that RRP1B physically interacts with many nucleosome binding factors, all of which have been implicated in regulation of gene expression. Examples include the linker histone H1X, poly(ADP-ribose) polymerase 1, tripartite motif-containing 28 (TIF-1β/KAP1), and cold shock domain protein A. These interactions were confirmed by co-immunofluorescence (Co-IF) and co-immunoprecipitation (Co-IP). Additionally, co-IF experiments demonstrated that RRP1B is localized to the perinuclear and perinucleolar regions, which is a particularly interesting given that factors localized to these regions are often involved in heterochromatinization and gene silencing. Furthermore, co-IP and co-IF demonstrated that RRP1B interacts with heterochromatin protein-1α and acetyl-histone H4 lysine 5, suggesting that RRP1B may well regulate gene expression through interactions with heterochromatin and euchromatin. Finally, we investigated the effects of ectopic expression of the 436Pro and 436Leu RRP1B allelic variants that have previously been associated with differential survival in breast cancer. Gene expression analyses demonstrate that, compared with ectopic expression of wildtype 436 Pro RRP1B in HeLa cells, the variant 436Leu RRP1B differentially modulates various transcription factors controlled by TRIM28 and CSDA. These data suggest that RRP1B, a tumor progression and metastasis susceptibility candidate gene, is potentially a dynamic modulator of transcription and chromatin structure. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2372.