Abstract B28: Cell type-dependent functions of cysteine cathepsins in murine breast cancer progression

Abstract In several human cancers elevated levels of lysosomal cysteine cathepsins correlate with poor prognosis. Transgenic overexpression of cathepsin B (CTSB) in the murine MMTV-PyMT model of breast cancer facilitates tumor invasion and metastasis1 whereas deficiencies of cathepsins B and Z synergistically attenuate these processes2. Notably, cathepsins are expressed in cancer cells as well as in cells of the tumor microenvironment. Our current investigations address the issue of cell-type specific functions of cathepsins B and Z in progression and metastasis of MMTV-PyMT mammary cancers by a combination of in vivo and in vitro approaches. Orthotopic implantation revealed that CTSB overexpression in cancer cells rather than in cells of the stroma affects tumor progression in this transgenic system. In 3D cultures primary PyMT cancer cells overexpressing CTSB revealed an elevated extracellular matrix degradation as well as an enhanced collective cell invasion. Co-cultivation of PyMT cancer cells with bone marrow derived macrophages induced a M2-polarized, tumor associated macrophage (TAM)-like phenotype and enhanced sprouting in tumor spheroids. A doxycycline (DOX)-inducible CTSB expression system was employed to selectively overexpress human CTSB in either cancer cells or in macrophages in 3D-cocultures. Interestingly, in this co-culture system selective overexpression of CTSB in either cancer cells or TAMs resulted in enhanced spheroid sprouting only if CTSB was overexpressed in the cancer cells. The carboxypeptidase cathepsin Z (CTSZ) is the only cysteine cathepsin harboring a RGD integrin binding motif. Expressing mutants of this enzyme revealed that the RGD motif is pro-invasive while the proteolytic activity is suppressing the invasive phenotype. The influence of the cysteine cathepsins CTSB and CTSZ on the secretome of PyMT cancer cells co-cultured with either wild-type or CTSB/CTSZ double knock macrophages was investigated by comparative proteomics. This approach revealed that the lysosomal glycoprotein CREG1 involved in cell proliferation and differentiation was significantly elevated in the secretome of the co-cultures with the double knock out macrophages. These results underline that cysteine cathepsins can have an impact on tumor invasion and metastasis on different levels, direct modification of the extracellular matrix as well as interference with putative signaling molecules. 1. Sevenich L, et al. Oncogene 2011; 30:54-64. 2. Sevenich L, et al. Proc Natl Acad Sci U S A 2010; 107: 2497-2502 Citation Format: Christoph Peters, Fee Bengsch, Kathrin Sachse, Alejandro Gomez-Auli, Oliver Schilling, Thomas Reinheckel. Cell type-dependent functions of cysteine cathepsins in murine breast cancer progression. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B28.