Figure 1: Expression of matriptase in the MMTV-PymT mammary carcinoma model and matriptase hypomorphic model.

(a) A knock-in mouse with a promoterless β-galactosidase marker gene inserted into the endogenous matriptase gene was used for precise assessment of endogenous matriptase expression in the mammary gland by X-gal staining (blue colour). Matriptase is expressed in the mammary gland epithelium (arrowhead in a) with no detectable expression in the stroma (*) in whole mounts from normal glands (left panel) and MMTV-PymT-induced carcinomas (middle panel). Histological analysis shows matriptase expression in the mammary cancer cells of MMTV-PymT transgenic mice (arrowhead, right panel). (b) Mammary epithelial cells from normal glands and tumour-bearing glands were isolated and analysed by western blotting (top panel) and gelatin zymography (lower panel) demonstrating increased levels of active matriptase in mammary carcinoma cells. (c) Western blot analysis of whole mammary gland extracts from matriptase hypomorphic mice (Mat^hypo) and control (Mat⁺) littermates with anti-matriptase (upper panel) or anti-HAI-1 (middle panel) antibodies. The levels of matriptase are greatly reduced in the Mat^hypo mice. Importantly, levels of the epithelia-specific, physiological matriptase inhibitor, HAI-1, are comparable in Mat^hypo and Mat⁺ glands. (d) Relative matriptase expression in Mat^hypo mice (N=3) and Mat⁺ mice (N=3) was determined by densitometry. Matriptase levels were normalized to HAI-1. Error bars represent s.d. P<0.04, Student’s t-test. (e) Immunohistochemical staining of mammary glands from virgin females with a sheep anti-matriptase antibody confirming that matriptase protein expression in the ductal epithelium is greatly reduced in the Mat^hypo mice. Scale bars, 50 μm.