Interplay Between TLR4 and Gelatinases in Tumour Growth and Metastasis

The modulation of the tumour microenvironment represents a pivotal step in tumorigenesis and metastasis and results from direct and paracrine cellular interactions. The innate immune Toll-like receptor 4 (TLR4) controls immune and inflammatory signalling in the tumour microenvironment. A growing body of evidence shows that TLR4 activation in cancer, immune and stromal cells upregulate gelatinase expression and activity, linking innate immune responses to extracellular matrix (ECM) remodelling. Gelatinases, or matrix metalloproteinases (MMP2) and (MMP9) play a pivotal role in tumour matrix degradation, thereby facilitating invasion, angiogenesis and metastasis. Interestingly, although TLR4 signalling in cancer cells and tumour-associated macrophages leads to different activation outputs, they can both induce gelatinases through NF-κB, MAPK, and Akt pathways. Evidence from clinical tumour tissues, co-culture models, in vivo and in vitro studies supports the crucial interplay between TLR4 signalling and gelatinases production in tumour growth and metastasis. An in-depth understanding of this crosstalk may reveal new therapeutic opportunities in targeted strategies.