Expression of RBM5-related factors in primary breast tissue.

The aim of this study was to examine the expression of the RBM5 tumor suppressor, in relation to RBM6 and RBM10, to obtain a better understanding of the potential role played by these RBM5-related factors in the regulation of RBM5 tumor-suppressor activity. Paired non-tumor and tumor samples were obtained from 73 breast cancer patients. RNA and protein expression were examined by semi-quantitative reverse transcription-polymerase chain reaction and immunoblot, respectively. Data were analyzed using various statistical methods to test for correlations amongst the RBM5-related factors, and between the factors and various pathological parameters. Most notably, RBM5, RBM10v1, and HER2 protein expression levels were elevated in tumor tissue (P < 0.0001). RBM5 and RBM10v1 protein expression were significantly positively correlated (P < 0.001), as were RBM5 and HER2 protein expression (P < 0.01), in both non-tumor and tumor tissue, whereas RBM10v1 and HER2 protein expression were only marginally correlated, in non-tumor tissue (P < 0.05). Interestingly, RBM5 and RBM10v1 protein expression were both deregulated in relation to RNA expression in tumor tissue. RBM10v2 and RBM6 RNA were highly significantly positively correlated in relation to various factors relating to poor prognosis (P < 0.0001). To our knowledge, this study is the first to examine RBM5 expression at both the RNA and protein level in primary breast tumor tissue, and the first to examine expression of all RBM5-related factors in a comprehensive manner. The results provide a graphic illustration that RBM5-related factors are significantly differentially expressed in breast cancer, and suggest complex inter-related regulatory networks involving alternative splicing, oncogenic expression, and tissue-specific function. J. Cell. Biochem. 100: 1440–1458, 2007. © 2006 Wiley-Liss, Inc.