Molecular signature associated with bone marrow micrometastasis in human breast cancer

Metastasis is the leading cause of cancer-related death, and bone marrow (BM) is a prominent metastatic site in solid tumors. Here, we focused on the onset of metastasis, using BM as an indicator organ for micrometastatic tumor cells in breast cancer patients without overt metastases (tumor-node-metastasis stage M0). Expression analysis with cDNA arrays showed distinct profiles between primary tumors from BM-positive and BM-negative patients. The differentially expressed genes are involved in extracellular matrix remodeling, adhesion, cytoskeleton plasticity, and signal transduction (in particular RAS and hypoxia-inducible factor la pathway). The BM signature was mainly characterized by transcriptional repression and different from the expression signature associated with lymphatic metastasis. Thus, BM micrometastasis is a selective process with a specific molecular signature of the primary tumor

Regulation of estrogen-dependent transcription by the LIM cofactors CLIM and RLIM in breast cancer

Mammary oncogenesis is profoundly influenced by signaling pathways controlled by estrogen receptor alpha (ERalpha). Although it is known that ERalpha exerts its oncogenic effect by stimulating the proliferation of many human breast cancers through the activation of target genes, our knowledge of the underlying transcriptional mechanisms remains limited. Our published work has shown that the in vivo activity of LIM homeodomain transcription factors (LIM-HD) is critically regulated by cofactors of LIM-HD proteins (CLIM) and the ubiquitin ligase RING finger LIM domain-interacting protein (RLIM). Here, we identify CLIM and RLIM as novel ERalpha cofactors that colocalize and interact with ERalpha in primary human breast tumors. We show that both cofactors associate with estrogen-responsive promoters and regulate the expression of endogenous ERalpha target genes in breast cancer cells. Surprisingly, our results indicate opposing functions of LIM cofactors for ERalpha and LIM-HDs: whereas CLIM enhances transcriptional activity of LIM-HDs, it inhibits transcriptional activation mediated by ERalpha on most target genes in vivo. In turn, the ubiquitin ligase RLIM inhibits transcriptional activity of LIM-HDs but enhances transcriptional activation of endogenous ERalpha target genes. Results from a human breast cancer tissue microarray of 1,335 patients revealed a highly significant correlation of elevated CLIM levels to ER/progesterone receptor positivity and poor differentiation of tumors. Combined, these results indicate that LIM cofactors CLIM and RLIM regulate the biological activity of ERalpha during the development of human breast cancer