Mammary tumour development is a complex process regulated by interactions between tumour cells and the surrounding microenvironment, particularly stromal cells and the extracellular matrix (ECM). The ECM exerts a great degree of cell-extrinsic regulation over cellular phenotype, providing cells with context-specific cues that guide cell and tissue programs. However, throughout breast cancer the ECM is spatio-temporally remodelled, providing tumour cells with the essential cues for malignant progression. We therefore hypothesized that stage- and region-dependant perturbations in the ECM facilitate progression in mammary cancer tumourigenesis.
To map the ECM through tumour development we used the Polyoma Middle-T (PyMT) mammary mouse tumour model, consisting of staged tumours (early, mid, and late) and age-matched healthy mammary tissue. Tumour histology ranged from benign hyperplasia to advanced metastatic carcinoma. ECM topology and composition was characterised using histological staining and multi-photon microscopy in order to quantitatively map structural organisation. Label-free quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS) was utilised in order to profile proteins within the evolving ECM system, or ‘matrisome’. Matrix-assisted laser desorption ionisation mass spectrometry imaging (MALDI-MSI) was used to map the spatial distribution of matrisomal protein profiles to breast and tumour histology. Key matrisomal proteins were then validated and targeted for functional investigation in in vitro and vivo models of tumour progression.
Our data identify 113 differentially regulated matrisomal proteins clustering into 4 distinct temporal profiles. Spatial mapping of key matrisomal proteins unveiled discrete localities within different tumour compartments, including stromal and cancer regions. We have identified a subset of matrisomal proteins demonstrating paralleled increased expression in the human setting, with protein expression negatively correlating with metastasis free survival. Systematic targeting of specific matrisomal proteins in stromal and cancer cell compartments has allowed us to dissect their functional role in tumour development and is facilitating the development of new potential stromal therapies to improve patient outcomes in breast cancer.