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 hypothesized that spatio-temporal perturbations in the ECM facilitate progression in mammary tumourigenesis.
To map the ECM through tumour development we used the Polyoma Middle-T (PyMT) mammary mouse tumour model, comprising staged tumours (early, mid, and late) and age-matched healthy mammary tissue. Tumour histology ranged from benign hyperplasia to advanced metastatic carcinoma. 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’. Differentially expressed proteins were cross-referenced to expression and survival data in the ‘The Cancer Genome Atlas’ (TCGA) and ‘Gene Expression Omnibus’ human breast cancer cohorts to reveal potential targets in breast cancer. Matrisomal proteins were then correlated to known drivers of progression within the matrix (i.e. collagen I) via histological staining and multi-photon microscopy. Single-cell RNA sequencing was used to delineate stromal cell expression of matrisomal proteins, and key proteins were 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. We have identified a subset of matrisomal proteins demonstrating paralleled increased expression in the human setting, with protein expression negatively correlating with progression 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, progression, and metastasis.
This exploratory analysis of the matrisome in breast cancer progression is facilitating the development of new potential stromal therapies to improve patient outcomes in breast cancer.