ECM internalisation as a novel modulator of cancer cell growth/survival

Tumour development is defined as a process in which cells constantly accumulate genetic mutations and epigenetic alterations. However, there is growing evidence that the tumour microenvironment including the extracellular matrix (ECM) also affects cancer cells survival, proliferation, growth, invasion and metastasis through cell-ECM interaction, cytokines, and growth factors. In addition, it is suggested that cancer cells rely on extracellular proteins during starvation, which is often observed in the tumour microenvironment due to elevated tumour growth rate and limited blood supply. Nonetheless, the role of ECM internalisation in cancer metabolism and regulatory mechanisms of this process have not been addressed in detail yet. Here we explored the role of ECM trafficking in terms of controlling breast cancer growth and survival. Our data demonstrate that the mechanisms through which cell-ECM interaction affects cancer cell growth varies by different starvation conditions. Under amino acid (AA) depletion, the presence of ECM could partially rescue the growth of invasive breast cancer cells (MDA-MB-231). Breast cancer cells were able to internalize and degrade collagen I and Matrigel under AA deficiency. In addition, inhibition of ECM uptake prevented cell growth under starvation. Our data show that presence of collagen I and Matrigel promotes cellular anabolic activity under AA starvation conditions by inducing mTORC1 activity. Mass-spectrometry data from AA starved cells on ECMs demonstrated significant increase in AA content as well as the upregulation of different metabolic pathways including phenylalanine and tyrosine metabolism, potentially increasing energy content of cells via fumarate formation. The data under non-essential AA (NEAA) starvation was also consistent to the AA starvation as cells required ECM internalization to rescue their growth. Monitoring candidate genes participating in ECM trafficking revealed three genes, RIN3, MAKP8IP3 and AP3D1 potentially having important role in trafficking of the ECM to the lysosome since their lack of function had adverse impact on invasive breast cancer cell growth under the NEAA deficiency. Under Glucose (Glc) starvation, MDA-MB-231 showed higher growth rate on ECM compared to the plastic. They could internalize ECM followed by lysosomal degradation. However, lack of ECM uptake did not oppose their growth. Whereas inhibition of focal adhesion kinase (FAK) activity substantially reduced their growth rate. Presence of ECM also enhanced mTORC1 activity in Glc starved cells. In contrast, ECM did not change metabolic content of cells after six days of Glc depletion. Thus, it is possible that the presence of ECM can trigger signaling pathways downstream of FAK inducing mTORC1 activity and cell growth. These findings lead to the conclusion that the presence of ECM could facilitate cancer cells growth/survival in nutrient deficient conditions via various mechanisms. There are different types of tumours that are surrounded by a dense and fibrotic stroma including breast, lung, pancreatic, and colon tumours. Therefore, the findings of this study could potentially be generalised to other types of cancers to find a potential therapeutic target in future.