Poster Presentation 9th General Meeting of the International Proteolysis Society 2015

Proteome analysis of interstitial fluid from murine breast cancers with differential cathepsin B expression (#120)

Alejandro Gomez Auli 1 2 3 , Larissa Hillebrand 1 3 , Martin Biniossek 1 , Christoph Peters 1 , Oliver Schilling 1 4 , Thomas Reinheckel 1 4
  1. Institute of Molecular Medicine and Cell Research, University of Freiburg, Freiburg, Germany
  2. Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, Germany
  3. Faculty of Biology, University of Freiburg, Freiburg, Germany
  4. BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany

Tumors are complex tissues, mainly constituted by cancer cells and surrounded by a rich tumor micro-environment (TM). The surrounding not only provides physical support; cancer and stromal cells secrete diverse proteins into the TM (cancer secretome), allowing a disturbed expression and secretion profile of proteins. Among these, proteases, such as cysteine cathepsin B, have been associated with tumorigenesis and worst prognosis.

The absence of cathepsin B (Ctsb) or the overexpression of the human cathepsin B (Tg(CTSB)) in the murine PyMT breast cancer model has proven to have contrasting effects. Its deficiency promotes an anti-tumorigenic effect while its overexpression endorses it; yet, the molecular mechanism responsible for the phenotypic change are still not completely understood. 

Sources of the cancer secretome mainly comprise the proximal biological fluids bathing the tumor, i.e. the interstitial fluid (IF), and its in-vitro surrogate, the cell-conditioned media. The former providing more relevant in-vivo information, although its collection and analysis has more challenges due to sample complexity. 

Using a novel strategy to collect the IF of solid tumors from the PyMT model of mice with altered cathepsin B expression coupled to mass-spectrometry based proteomics methods, we have been able to compare secretome changes due to absence of Ctsb or Tg(CTSB) overexpression. Good proteome coverage (~1700 proteins) with enrichment of secreted proteins was observed. A small subset of differentially regulated proteins with opposite regulation were identified. These include plasma glycoproteins like alpha-1B-glycoprotein and proteins from the major urinary protein family, which despite their name, have been observed in plasma, breast, among other locations. 

Breast cancers secretome changes due to cathepsins B expression were analyzed and potential candidates, which may account for the change in phenotype previously reported, have been identified. Further studies are being made to determine the roles the identified proteins may have in this model.