Long Non-Coding RNA and Polycomb Protein Expression Levels Are Increased in Metastatic Versus Primary Breast Carcinoma
Karen M Chisholm, Rui Li, Yue Wan, Howard Chang, Robert B West. Stanford University School of Medicine, Stanford, CA
Background: Tumor development involves the alteration of gene expression patterns due to epigenetic changes. Polycomb group (PcG) proteins work in multiprotein complexes called Polycomb Repressive Complexes (PRCs) that repress transcription of gene expression by modification of chromatin. EZH2, the enhancer of zeste homolog 2, is a PcG protein in the PRC2 complex. Long intervening non-coding RNA (lincRNAs) may be one of the regulators of PcG proteins. Experimental evidence suggests that in cancer, lincRNAs can influence Polycomb repressive complexes to retarget to an occupancy pattern resembling that of the embryonic state. HOTAIR lincRNA has been reported to be increased in primary tumors and metastases, and its expression level in primary tumors a predictor of eventual metastasis and death. The current project is undertaken to determine if HOTAIR lincRNA and EZH2 Polycomb protein have increased expression in matched primary and metastatic breast carcinomas.
Design: An RNA in situ hybridization probe of 400 to 500 nucleotides was created for HOTAIR. EZH2 expressed was evaluated by immunohistochemistry (BD Transduction Laboratories, clone 11). These two markers were examined on two breast cancer microarrays containing 283 primary breast carcinomas and 110 matched metastases. The stains were scored by eye on a three-tiered scoring system, and the scores from matched primary and metastatic breast cancers were correlated. Statistics were performed using a two-tailed Fisher exact test and Chi-squared test.
Results: In matched primary and metastatic cancers, both HOTAIR and EZH2 had increased expression in the metastatic carcinomas. From primary to matched metastatic carcinoma, 93% of pairs had an increased or equivalent EZH2 expression, and 40% had an increased EZH2 expression, while 83% of pairs had an increased or equivalent HOTAIR expression, and 52% had an increased HOTAIR expression. In addition, EZH2 and HOTAIR expression levels were highly correlated (p = <0.0001).
Conclusions: This is the first study to look at matched primary and metastatic breast cancers and correlate EZH2 protein and HOTAIR expressions in archival material. The data support increased expression of both the protein and the lincRNA in metastatic cancer, compared to primary carcinomas. This protein together with this lincRNA may be influencing chromatin remodeling and the expression of other proteins to increase cancer invasiveness.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 61, Wednesday Morning