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Daniel Kirchhofer Senior Scientist: Protein Engineering |
"Cancer cell surface proteases
We are studying the function of proteases of the 'Type II Transmembrane Serine Protease' (TTSP) family and their endogenous inhibitors in cancer progression. For instance, the TTSP hepsin is highly overexpressed in prostate cancer and promotes tumor progression and metastasis. Recent in-vivo studies with hepsin-overexpressing prostate cancer cells suggest that hepsin is also involved in primary tumor growth. We were able to identify two macromolecular substrates for hepsin, pro-HGF and pro-urokinase as well as the hepsin inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1), a cell surface-expressed bi-Kunitz inhibitor. HAI-1 and its potent Kunitz domain-1 fragment also inhibit the TTSP matriptase and the GPI-anchored serine protease prostasin. Studies by Bin Fan (2007) with HAI-1-/- mice suggested that HAI-1 has a critical role in regulating matriptase and perhaps also prostasin activity in the developing placental labyrinth. We are currently using various in-vitro and in-vivo models to understand the proteases' roles in tumor progression. Moreover, we are utilizing structural and biochemical approaches to gain insight into the molecular function and regulation of hepsin, matriptase and other TTSPs family members.
Hepatocyte growth factor (HGF)/Met signaling
The HGF/Met pathway is not only important for development and tissue regeneration but also for invasive tumor growth and, therefore, an interesting therapeutic target. An important regulatory step for HGF/Met signaling is the processing of single chain HGF into the signaling-competent two-chain form by HGF convertases, such HGF activator (HGFA). Several inhibitory anti-HGFA antibodies were identified by use of phage display technology and the subsequently obtained Fab/HGFA crystal structures provided insight into the molecular inhibition mechanism of allosteric and active site binding antibodies. Based on the structural kinship of the HGF β-chain to the protease domain of serine proteases, we hypothesized that HGF convertase-mediated activation cleavage results in the conformational rearrangement of the "activation domain" on HGF β, leading to the formation of a new Met binding site. The subsequent biochemical, mutagenesis and structural studies (in collaboration with Lazarus and Wiesmann labs) confirmed this and allows us to investigate novel and specific inhibitory approaches to interrupt HGF signaling by targeting the HGF β-chain."