Tissue inhibitor of metalloproteinases-1-induced scattered liver metastasis is mediated by hypoxia-inducible factor-1 α

The "protease web", representing the network of proteases, their inhibitors, and effector molecules, arises as a pivotal determinant of tissue homeostasis. Imbalances of this network, for instance caused by elevated host levels of tissue inhibitor of metalloproteinases-1 (TIMP-1), have been shown to increase the susceptibility of target organs to scattered metastasis by inducing the hepatocyte growth factor (HGF) pathway. Increased expression of the hypoxia-inducible factor-1a-subunit (HIF-1α) is also associated with tumour progression and is also known to induce HGF-signaling via up-regulation of the HGF receptor Met, namely under canonical stress conditions like lack of oxygen. Here, we aimed to identify a possible metastasis-promoting connection between TIMP-1, HIF- 1α, and HGF-signaling. We found that HIF-1α and HIF- 1-signaling were increased during liver metastasis of L-CI.5s T-lymphoma cells in TIMP-1 overexpressing syngeneicDBA/2 mice. In vitro, exposure of L-CI.5s cells to recombinant TIMP-1 revealed that TIMP-1 itself was able to induce HIF-1α and HIF-1-signaling. Knock-down of HIF-1α identified tumour cell-derived HIF-1α as mediator of this TIMP-1-induced invasiveness in vitro. In vivo, HIF-1α knock-down significantly impaired Met expression as well as Met phosphorylation and inhibited scattered liver metastasis. Furthermore, HGF-dependent TIMP-1-promoted Met phosphorylation and HGF-dependent TIMP- 1-induced invasiveness in vitro was mediated by HIF-1α. We conclude that elevated levels of TIMP-1 in the microenvironment of tumour cells can promote metastasis by inducing HIF-1α-dependent HGF-signaling. This connection between a protease inhibitor (TIMP-1) and a classically stress-related factor (HIF-1α) is a so far undiscovered impact of the "protease web" on tissue homeostasis with important implications for metastasis.