Differential gene expression of selective TGF-β family members and osteopontin in breast tumor tissue: Analysis by real-time quantitative PCR

Several cytokines including members of the TGF-β and TNF families have been implicated in the homing mechanism of breast cancer metastasis. We hypothesize that primary breast tumor tissues differentially express modulators of bone cell function that contribute to their aggressive and metastatic potential and to their capacity to establish and grow in bone. We examined the gene expression pattern of the TGF-β family members (activin β-A subunit, inhibin α subunit, and bone morhogenetic protein-2 (BMP-2)), the TNF family members (receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG)), as well as osteopontin (OPN) in normal, non-invasive, invasive, and metastatic human breast cancer specimens. Methods: The level of mRNA transcripts of these genes in 18 normal breast tissues, 5 ductal carcinoma in situ (DCIS), 24 primary breast tumor tissues, and 5 distant metastases were quantitated by reverse transcription (RT) and fluorescent-based kinetic PCR. Results: We observed differential gene expression of the selected TGF-β family members as well as OPN in breast cancer progression. The average gene expression of the putative tumor suppressor, inhibin α, did not significantly change in any of the tumor tissues examined compared to normal breast tissue. The mRNA level of BMP-2, a protein with anti-proliferative effects in breast cancer cell lines and involved in bone formation, significantly decreased in the different stage breast tumor tissues compared to normal breast tissue. Gene expression of activin β-A, a protein involved in cell proliferation and osteoclast induction, increased in invasive tumor tissue and bone metastasis compared to normal and non-invasive breast tissue. The mRNA level of OPN. a bone matrix protein associated with enhanced malignancy, increased in DCIS. primary tumor tissue, and liver and bone metastases compared to normal breast tissue. In contrast, the average gene expressions of the TNF family members. RANKL and OPG. proteins involved in the regulation of osteoclastogenesis. were only slightly if at all changed in the different stage breast tumor tissues. Conclusion: These results suggest that the TGF-β pathway and OPN may play a more significant role than the TNF pathway in breast cancer invasiveness, metastases and its ability to establish and grow in bone.