Different molecular profiles are associated with breast cancer cell homing compared with colonisation of bone: evidence using a novel bone-seeking cell line

Abstract

Advanced breast cancer is associated with the development of incurable bone metastasis. The two key processes involved, tumour cell homing to and subsequent colonisation of bone, remain to be clearly defined. Genetic studies have indicated that different genes facilitate homing and colonisation of secondary sites. To identify specific changes in gene and protein expression associated with bone-homing or colonisation, we have developed a novel bone-seeking clone of MDA-MB-231 breast cancer cells that exclusively forms tumours in long bones following i.v. injection in nude mice. Bone-homing cells were indistinguishable from parental cells in terms of growth rate in vitro and when grown subcutaneously in vivo. Only bone-homing ability differed between the lines; once established in bone, tumours from both lines displayed similar rates of progression and caused the same extent of lytic bone disease. By comparing the molecular profile of a panel of metastasis-associated genes, we have identified differential expression profiles associated with bone-homing or colonisation. Bone-homing cells had decreased expression of the cell adhesion molecule fibronectin and the migration and calcium signal binding protein S100A4, in addition to increased expression of interleukin 1B. Bone colonisation was associated with increased fibronectin and upregulation of molecules influencing signal transduction pathways and breakdown of extracellular matrix, including hRAS and matrix metalloproteinase 9. Our data support the hypothesis that during early stages of breast cancer bone metastasis, a specific set of genes are altered to facilitate bone-homing, and that disruption of these may be required for effective therapeutic targeting of this process.

Molecular alterations that drive breast cancer metastasis to bone

“…2 Using a similar approach in which bone-homing clones of MDA-MB-231 cells were compared with parental cells, we and others have found that bone homing is associated with decreased cellcell adhesion and migration, coupled with significantly reduced levels of the cell adhesion molecule fibronectin and calcium signal binding protein S100A4. 65,66 Interestingly, we also found a strong link between IL-1B expression and bone homing in both MDA-MB-231 cells and primary tumours from breast cancer patients, indicating that this molecule may promote an invasive and motile phenotype in breast cancer cells. 66 In fitting agreement with the hypothesis that breast cancer cells acquire genotypic similarities to cancer stem cells during EMT and progression to bone metastasis, Hiraga et al 67 showed that CD44 overexpression in breast, myeloma and prostate cancer cells promotes bone metastasis by enhancing tumourigenicity, cell migration, invasion and production of extracellular matrix haluronan.…”

“…65,66 Interestingly, we also found a strong link between IL-1B expression and bone homing in both MDA-MB-231 cells and primary tumours from breast cancer patients, indicating that this molecule may promote an invasive and motile phenotype in breast cancer cells. 66 In fitting agreement with the hypothesis that breast cancer cells acquire genotypic similarities to cancer stem cells during EMT and progression to bone metastasis, Hiraga et al 67 showed that CD44 overexpression in breast, myeloma and prostate cancer cells promotes bone metastasis by enhancing tumourigenicity, cell migration, invasion and production of extracellular matrix haluronan. Whether high expression of CD44 is because of these cell lines having high numbers of cancer stem cells or whether this is a result of EMT-induced expression of CD44 remains to be established.…”

“…2 However, it should be noted that expression of CXCR4 is not a universal feature in breast cancer bone homing. We and others have generated bone-homing clones of MDA-MB-231 cells (BO2 and MDA-IV cells) using the same method as described by Kang et al 2,65,66 Interestingly, CXCR4 was not detected in either of these bone-homing cell lines by microarray or PCR analysis.…”

“…Once in the bone microenvironment, it is hypothesised that breast cancer cells compete for the HSC niche, and once within this niche, they can be stimulated to proliferate. 66,75 In addition to molecules with well-defined roles in bone colonisation, discussed below, we have previously demonstrated that this process is also associated with increased levels of MMP9, HRAS and fibronectin. 66 MMP9 has strong associations with increased tumour cell invasion in a number of cancer types, 63 and increased MMP9 expression has been shown to increase the capacity of tumour cells to extravasate as well as to cause activation of bone-resorbing osteoclasts.…”

Tumour-derived miRNAs and bone metastasis

“…5 Following tumour cell dissemination into the blood and/or lymphatic system, if the cancer cells are resistant to anoikis and escape the immune surveillance, these cells must express a specific gene signature to disseminate to bone, invade the bone marrow, adapt to the local microenvironment and finally exit the dormancy step to further colonise the tissue. 2,6,7 Each of the molecular pathways underlining these steps is regulated by multiple factors, through the tight control of genes expressed by cancer cells interacting with cells of the bone microenvironment. 8,9 Small non-coding microRNAs (miRNAs) are master regulators of gene expression which have the capacity to regulate multiple genes and thus to redirect or reprogram biological pathways.…”