KLK6-mediated CXCL1 production was required for tumor growth and metastasis. (A) Mouse cytokine array in serum from WT or KLK6−/− mice injected with PBS (control) or B16F10 melanoma cells. (B,C) 1 × 106 of B16F10 cells were subcutaneously (B) or intravenously (C) injected into WT and KLK6−/− mice (n = 8 per group). CXCL1 and CXCL2 levels in serum from WT and KLK6−/− mice injected with B16F10 melanoma cells were measured by ELISA as described in the Materials and Methods. (D,E) 1 × 106 of B16F10 cells were subcutaneously injected into WT mice (n = 6 per group). After 1 h, mice were injected with PBS (control) or CXCL1 neutralizing antibody (5 mg/kg) every other day for 10 days. (D) Representative photograph of the tumors. (E) Tumor volume was measured as described in the Materials and Methods. (F,G) 5 × 105 of B16F10 cells were intravenously injected into the tail vein of WT mice (n = 8 per group). After 1 h, the mice were injected with PBS (control) or CXCL1 neutralizing antibody (5 mg/kg) every other day for 10 days. (F) Representative photograph of metastatic lung nodules. (G) The number of metastatic lung nodules was calculated as described in the Materials and Methods. ** p < 0.01 and * p < 0.05 (Student’s t-test). Data are representative of three experiments.