Although both recombinant KD1 and KD2 of HAI-2 were able to inhibit and interact with matriptase in the in vitro study (Figs 5 and 6), cellular HAI-2 tended to harness its KD1 to represses matriptase activation as well as prostate cancer cell motility, rather than its KD2 (Figs 7 and 8). This evidence concerns the gene SPINT2 and prostate cancer.