Increased expression of a set of genes enriched in oxygen binding function discloses a predisposition of breast cancer bone metastases to generate metastasis spread in multiple organs

Bone is the preferential site of distant metastasis in breast carcinoma (BrCa). Usually patients with metastasis restricted to bone (BO) show a longer overall survival compared to patients who rapidly develop multiple metastases involving also liver and lung. Hence, molecular predisposition to generate bone and visceral metastases (BV) represents a clear indication of poor clinical outcome. We performed microarray analysis with two different chip platforms, Affymetrix and Agilent, on bone metastasis samples from BO and BV patients. The unsupervised hierarchical clustering of the resulting trascriptomes correlated with the clinical progression, segregating the BO from the BV profiles. Matching the 2-fold significantly regulated genes from Affymetrix and Agilent chips resulted in a 15 gene signature with 13 up- and 2 down-regulated genes in BV versus BO bone metastasis samples. In order to validate the resulting signature, we isolated different MDA-MB-231 clonal subpopulations that metastasize only in the bone (MDA-BO) or in bone and visceral tissues (MDA-BV). Six of the signature genes were also significantly up-regulated in MDA-BV compared to MDA-BO clones. A group of up-regulated genes, including Hemoglobin B (HBB), were involved in oxygen metabolism, and in vitro functional analysis of HBB revealed that its expression in the MDA subpopulations was associated with a reduced production of hydrogen peroxide. Expression of HBB was detected in primary BrCa tissue but not in normal breast epithelial cells. Metastatic lymph nodes were frequently more positive for HBB compared to the corresponding primary tumors, while BO metastases had a lower expression than BV metastases, suggesting a positive correlation between HBB and ability of bone metastasis to rapidly spread to other organs. We propose that HBB, along with other genes involved in oxygen metabolism, confers a more aggressive metastatic phenotype in BrCa cells disseminated to bone. \ua9 2012 American Society for Bone and Mineral Research. Copyright \ua9 2012 American Society for Bone and Mineral Research. PMID:22714395[PubMed - as supplied by publisher