Regulation of site-specific liver metastasis by extracellular matrix proteins

Metastatic disease remains the main cause of death from cancer. Few therapeutic options for patients have demonstrated potential in curing metastatic disease. The molecular mechanisms underlying site-specific metastasis and the factors mediating tumor cell homing remain largely unknown. Based on a murine Lewis lung carcinoma tumour model of site-specific metastasis mediated by the expression of the insulin-like growth factor -- I receptor (IGF-IR), we identified ECM components that show particular promise in regulating metastasis to a specific site. Specifically, we identified collagen IValpha1 and alpha2 as differentially expressed in liver- and lung-colonizing cells. The overexpression of these genes caused major changes to cell structure and function including differences in cellular morphology, anchorage-independent growth, and resulted in a switch from a lung- to a liver-metastasizing phenotype. These changes were at least in part due to alpha2-integrin-mediated activation of focal adhesion kinase (FAK) and protection from anoikis. Collagen IV alpha1 suppression resulted in increased anoikis and decreased tumour cell colonization of the liver, making it an essential and sufficient gene in liver metastasis in our model. Moreover, type IV collagen overexpression resulted in major changes to ECM and ECM-degradation genes decreasing MMP-3, MMP-9, MMP-13, and collagen type III. Uveal melanoma cells with distinct metastatic phenotypes also showed major changes to these genes. Finally, by analyzing human specimens of metastatic disease, collagen IV was shown to be expressed only in metastatic and specifically hepatic metastases when compared to primary tumours and metastases to other organs. Collectively, these findings implicate collagen IV as a clinically relevant marker and potential target against site-specific metastasis to the liver.