LOX activity assay.

LOX activity of recombinant human LOXL2 or conditioned medium collected from cells expressing LOXL2 was measured using a Fluorometric Lysyl Oxidase Activity Assay Kit (ab112139, Abcam) following a protocol provided by the manufacturer. Briefly, 50 μl of sample was mixed with an equal volume of assay reaction mixture containing LOX substrate, HRP, and HRP substrate in the presence and absence of testing inhibitors and d-penicillamine (DPA), a LOX inhibitor. The mixture was incubated for 30 minutes at 37°C in darkness. The fluorescence increase was then measured with a fluorescence plate reader (BMG LabTech FLUOstar) at excitation (Ex)/emission (Em) = 540/590 nm. Sample buffer or medium alone without LOXL2 was used for determination of the background fluorescence.