Proteolysis-a characteristic of tumor-initiating cells in murine metastatic breast cancer.

Larissa E Hillebrand,Julia Bender,Jan Hülsdünker,Jochen Hochrein,Hauke Busch,Melanie Boerries,Fee Bengsch,Marie Follo,Thomas Reinheckel

doi:10.18632/oncotarget.11309

Larissa E Hillebrand, Julia Bender + Show 7 more

Open Access

https://doi.org/10.18632/oncotarget.11309

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Abstract

Tumor initiating cells (TICs) have been identified and functionally characterized in hematological malignancies as well as in solid tumors such as breast cancer. In addition to their high tumor-initiating potential, TICs are founder cells for metastasis formation and are involved in chemotherapy resistance. In this study we explored molecular pathways which enable this tumor initiating potential for a cancer cell subset of the transgenic MMTV-PyMT mouse model for metastasizing breast cancer. The cell population, characterized by the marker profile CD24+CD90+CD45−, showed a high tumorigenicity compared to non-CD24+CD90+CD45− cancer cells in colony formation assays, as well as upon orthotopic transplantation into the mammary fat pad of mice. In addition, these orthotopically grown CD24+CD90+CD45− TICs metastasized to the lungs. The transcriptome of TICs freshly isolated from primary tumors by cell sorting was compared with that of sorted non-CD24+CD90+CD45− cancer cells by RNA-seq. In addition to more established TIC signatures, such as epithelial-to-mesenchymal transition or mitogen signaling, an upregulated gene set comprising several classes of proteolytic enzymes was uncovered in the TICs. Accordingly, TICs showed high intra- and extracellular proteolytic activity. Application of a broad range of protease inhibitors to TICs in a colony formation assay reduced anchorage independent growth and had an impact on colony morphology in 3D cell culture assays. We conclude that CD24+CD90+CD45− cells of the MMTV- PyMT mouse model possess an upregulated proteolytic signature which could very well represent a functional hallmark of metastatic TICs from mammary carcinomas.

Highlights

Malignant tumors consist of heterogeneous cancer cell populations [1]
Tumor cells positive for the cell surface markers CD24 and CD90 are known for their high tumorigenicity in the transgenic MMTV-Wnt1 mouse model and have been called cancer stem cells [15]
Cells expressing the common leukocyte antigen CD45 were always excluded from the CD24+CD90+ population, which resulted in a doublepositive population constituting 0.11 to 1.4 percent of the CD45 negative cells in the tumor (Figure 1A)

Summary

Introduction

Malignant tumors consist of heterogeneous cancer cell populations [1]. Understanding the functional and therapeutic implications of this heterogeneity has become a major challenge for basic and translational cancer research [2, 3]. Cancer stem cells were first identified in hematological malignancies by Bonnet and Dick [5] This concept has been established for a number of epithelial derived www.impactjournals.com/oncotarget cancers, such as colon, prostate, breast, and pancreatic carcinomas [3, 6,7,8,9]. Malignant stem cells from carcinomas are thought to be motile and, able to establish metastases in distant organs [12]. Due to their cancer-forming ability, and in order to distinguish them from physiological stem cells in tissues, these cells are often referred to as tumor initiating cells (TICs); a term which we will use hereafter

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