Carcinoma and stromal enzyme activity profiles associated with breast tumor growth in vivo

Abstract

Cancer research depends on the use of human cell lines for both the in vitro (culture) and in vivo (xenograft) analysis of tumor progression and treatment. However, the extent to which cultured preparations of human cancer lines display similar properties in vivo, where important host factors may influence tumor biology, remains unclear. Here, we address this question by conducting a functional proteomic analysis of the human breast cancer line MDA-MB-231 grown in culture and as orthotopic xenograft tumors in the mammary fad pad of immunodeficient mice. Using a suite of activity-based chemical probes, we identified carcinoma (human) enzyme activities that were expressed selectively in culture or in xenograft tumors. Likewise, distinct groups of stromal (mouse) enzyme activities were found that either infiltrated or were excluded from xenograft tumors, indicating a contribution by specific host components to breast cancer development. MDA-MB-231 cells isolated from tumors exhibited profound differences in their enzyme activity profiles compared with the parent cell line, including the dramatic posttranscriptional up-regulation of the serine proteases urokinase plasminogen activator and tissue plasminogen activator and down-regulation of the glycolytic enzyme phosphofructokinase. These altered enzyme activity profiles correlated with significantly greater tumor growth rates and metastases for xenograft-derived MDA-MB-231 cells upon reintroduction into mice. Collectively, these data indicate that the in vivo environment of the mouse mammary fat pad cultivates the growth of human breast cancer cells with elevated tumorigenic properties and highlight the value of activity-based protein profiling for identifying proteomic signatures that depict such changes in cancer cell biology.T umorigenesis involves an intricate crosstalk between cancer cells and the nontumor (stromal) environment (1-3). Host or stromal factors can be both supportive and responsive to tumors and have been shown to play key roles in fostering the development of cancer in several experimental models. For example, both carcinoma-associated fibroblasts (4) and fibroblasts subjected to irradiation (5) have been found to promote transformation of nontumorigenic epithelial cells. Likewise, the deletion of specific host proteases (6) or protease inhibitors (7) impedes tumor progression in vivo. For breast cancer, in particular, the orthotopic host environment appears to play a uniquely supportive role, as the mouse mammary gland and surrounding mesenchymal tissue, the mammary fat pad (mfp), allow human breast cancer cells to form tumors more readily than nonorthotopic sites [e.g., the subcutis (8)]. Although an intimate relationship clearly exists between the growing tumor and surrounding stromal environment, the molecular changes induced in cancer cells by host factors remain largely unknown.Determining the impact of stromal influence on the molecular and cellular properties of tumor cells is especially relevant for the study of human cancer cell lines, ...

Preclinical evaluation of 213Bi-labeled plasminogen activator inhibitor type 2 in an orthotopic murine xenogenic model of human breast carcinoma

“…Tumors xenografted into the mammary fat pads of mice using human MDA-MB-231 express human uPA and uPAR (4,27). As previously shown (28), we found heterogeneous human uPA immunoreactivity in sections of the tumor xenografts and the overall degree of staining varied between individual tumors (Fig.…”

Tumor–stromal interactions reciprocally modulate gene expression patterns during carcinogenesis and metastasis

“…Recently, convincing evidence of interactions between individual genes or categories of genes (e.g., enzymes) in neoplastic and nonneoplastic cells within tumors has appeared in some reports. 16,[36][37][38][39][40] Moreover, Creighton et al 41 conducted global gene expression analysis and showed a network of tumor-stromal molecular interactions in a primary tumor xenograft model of lung cancer. Our current report now provides specific evidence that, during metastasis, labeled cancer cells and neighboring host cell lineages of 3 different organs (breast, lung and lymph node), reproducibly and reciprocally alter the expression of multiple groups of genes coordinately, upon encountering each other and/or the intercellular materials that they produce.…”

Posttranslational Protein Modifications

“…Proteases, kinases, and phosphatases have been investigated by this approach. Serine hydrolases, a class of protease, and sialyl acetylesterase, an enzyme modifying sugar moieties of glycoproteins, were analyzed by certain fluorophosphonate probes to characterize breast and melanoma cancer cell lines (44,45). Distinctions in their subcellular distribution and activity expression patterns within each class of enzymes were found to distinguish the source of tumors and predict the invasive nature of the cancer cells.…”