TMPRSS6 expression is induced by BMP6. (A) Hep3B cells were treated with 5, 25, and 50 ng/mL of human BMP6 for 16 hours and were analyzed for hepcidin and TMPRSS6 relative to RPL19 mRNA expression by quantitative real-time RT-PCR. The mean of 3 to 8 (depending of the dose) independent experiments is presented. Results are reported as the mean ± SEM for the fold change from mock, and significant changes represent the comparisons with mock. (B-C) Hep3B cells were transfected with siRNA control (5nM), siRNA TMPRSS6 (5nM), or TMPRSS6-FLAG (8 μg), and treated with 25 ng/mL of BMP6 for 48 hours. Cells were analyzed for matriptase-2 level relative to pan-cadherin protein by Western blot (B) followed by chemiluminescence quantification (C). (B) *A shorter exposure of lane 5 to better distinguish the 2 bands. (C) The mean of 3 experiments is presented, and results are reported as the mean ± SEM. (D) A total of 15 μg of protein from conditioned media of Hep3B cells transfected with siRNA control (5nM) and siRNA TMPRSS6 (5nM) and treated with BMP6 (25 ng/mL) for 48 hours were incubated with 666μM of N-(tert-butoxycarbonyl)-Gln-Ala-Arg-p-nitroanilide. Activity of matriptase-2 was assessed by measurement of the release of the dye p-nitroaniline during up to 20 minutes at a wavelength of 405 nm at 37°C using a spectrophotometer. The resulting activities (1 U corresponds to a release rate of 1 mmol of p-nitroaniline per minute) were measured in duplicate in 3 independent experiments. Results are reported as the mean ± SEM. (A,C-D) Significant changes are as follows: *P < .05; **P < .01; and ***P < .005.