Tumor microenvironment constitutes a reservoir for
proteins released from
tumor cells and the host, which can contribute significantly to
tumor growth and invasion. This study aims to apply a method of combining in vivo microdialysis and proteomics to identify
proteins in mammary
tumor interstitial fluids, a major component of tumor microenvironment. In vivo microdialysis was performed in polyomavirus middle
T antigen (PyVmT) transgenic mouse mammary
tumors and age-matched control wild-type mammary glands. Over four hundred
proteins were identified from the microdialysis perfusates, using the Multidimensional
Protein Identification Technology.
Osteopontin (OPN) is one of the
proteins overexpressed in
breast tumor perfusates, as confirmed with immunoassays. OPN was also found to be present in
tumor-associated stroma in both PyVmT and human
breast tumors, using immunohistochemistry. Specifically, fibroblasts were further shown to express OPN at both
mRNA and
protein levels. In vitro assays showed that OPN can stimulate PyVmT
breast carcinoma cell proliferation and migration. Finally, the expression of OPN was significantly higher in the peripheral blood of mice bearing
breast tumors, compared to wild-type mice. Overall, microdialysis combined with proteomics is a unique technique for identifying
proteins in a tumor microenvironment in vivo. Mammary fibroblasts can secrete OPN, and its overexpression in mammary tumor microenvironment may contribute significantly to mammary
tumor progression.
ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12307-010-0046-3) contains supplementary material, which is available to authorized users.