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Secretory products of breast cancer cells specifically affect human osteoblastic cells: partial characterization of
B Siwek1, M Lacroix, C De Pollak
1Bone Metabolism Unit, Institut J. Bordct, Université Libre de Bruxelles, Belgium.
Abstract:
The pathogenesis of tumor-induced osteolysis (TIO) following breast cancer metastases in bone remains unclear. We postulated that osteoblasts could be target cells for the secretory products of breast cancer cells. We previously showed that serum-free conditioned medium (CM) of the breast cancer cell line MCF-7 inhibits DNA synthesis by 75% of control values in osteoblast-like cells SaOS-2 and that this effect is only in a minor part due to transforming growth factor beta secretion. To establish the specificity of our observations and to look for other biologically active factors, we have tested the effects of medium conditioned by several cancer and noncancer cell lines (breast, colon, placenta, or fibrosarcoma) on the proliferation of osteoblast-like cells (SaOS-2, MG-63), normal human osteoblasts, human fibrosarcoma cells, and normal human fibroblasts. Culture medium (1:2) of the breast cancer cell lines MCF-7, T-47D, MDA-MB-231, and SK-BR-3 inhibited by 25-50% the proliferation of osteoblast-like cells SaOS-2, MG-63, and normal osteoblasts as evaluated by the MTT survival test or [3H]thymidine incorporation. MCF-7 cells completely inhibited the proliferation of normal human osteoblasts in coculture. This inhibitory effect was reversible and not due to cytotoxicity. Moreover, the cyclic adenosine monophosphate (cAMP) response to parathyroid hormone (PTH) of osteoblast-like cells SaOS-2 was also increased by 100-240% by the same CM. Such activities were, however, not detected in medium from the breast noncancer cell line HBL-100 or in the medium conditioned by non-breast cancer cell lines (COLO 320DM, HT-29, JAR, or HT-1080). Medium from the breast cancer cells had no effect on normal human fibroblasts or fibrosarcoma cells (HT-1080), suggesting the specificity of their action on human osteoblasts. After partial purification by ultrafiltration and size-exclusion chromatography, we found that medium of T-47D cells contained at least three nonprostanoid factors of low molecular weights (apparent MW of 700, 1500, and 4000 D) which affected human osteoblast-like cells. These factors were heat stable and could be peptides without disulfide bonds. In summary, our data show that human breast cancer cells release soluble factors that inhibit osteoblast proliferation and increase their cAMP response to PTH, indicating that osteoblasts could be important target cells for breast cancer cells and could be involved in the process of TIO.
Insights
Breast cancer cells release factors that inhibit osteoblast proliferation and alter their response to parathyroid hormone (PTH), suggesting osteoblasts are key targets in tumor-induced osteolysis (TIO).
Area of Science:
- Cell Biology
- Oncology
- Biochemistry
Background:
- Tumor-induced osteolysis (TIO) in breast cancer bone metastases is a significant clinical problem.
- The precise mechanisms driving TIO, particularly the interaction between cancer cells and bone cells, remain incompletely understood.
- Previous research indicated breast cancer cell secretions might affect osteoblast function.
Purpose of the Study:
- To investigate whether breast cancer cells secrete factors that directly impact osteoblast proliferation and function.
- To determine the specificity of these effects on osteoblasts compared to other cell types.
- To identify potential characteristics of these secreted factors.
Main Methods:
- Culturing various breast cancer cell lines (MCF-7, T-47D, MDA-MB-231, SK-BR-3) and non-cancerous cell lines.
- Treating osteoblast-like cells (SaOS-2, MG-63), normal human osteoblasts, fibroblasts, and fibrosarcoma cells with conditioned media (CM).
- Assessing cell proliferation using MTT assays and [3H]thymidine incorporation.
- Measuring cyclic adenosine monophosphate (cAMP) response to parathyroid hormone (PTH) in osteoblast-like cells.
- Partial purification of active factors from conditioned media using ultrafiltration and chromatography.
Main Results:
- Conditioned media from multiple breast cancer cell lines significantly inhibited osteoblast proliferation (25-50%) and normal osteoblast proliferation (up to 100%).
- This inhibitory effect was reversible, non-cytotoxic, and specific to osteoblasts, with no impact on fibroblasts or fibrosarcoma cells.
- Breast cancer cell conditioned media increased the cAMP response to PTH in osteoblast-like cells by 100-240%.
- Active factors were heat-stable, low molecular weight (700, 1500, 4000 D), nonprostanoid, and potentially peptide in nature.
Conclusions:
- Human breast cancer cells secrete soluble factors that inhibit osteoblast proliferation.
- These factors also modulate osteoblast response to parathyroid hormone (PTH).
- Osteoblasts are likely important target cells for breast cancer cells, playing a role in the pathogenesis of tumor-induced osteolysis (TIO).