Figure 1.

Vitamin D3 increases legumain expression, activity, and secretion in pre-osteoblastic cells. (A) The nucleotide sequence of the LGMN gene promoter region with annotations of potential vitamin D-responsive elements (VDRE; red) relative to the transcription start site (TSS). (B–F) Human BMSC-TERT cells (20,000 cells/cm²) were incubated with 1,25(OH)₂D₃ (B–F; 10, 50 or 100 nM), 25(OH)D₃ (C–F; 100, 250, 500 or 1000 nM) or an equal volume of ethanol (control, 0 nM) in osteoblast induction medium for seven days before harvesting. (B) Legumain mRNA expression relative to housekeeping control (GAPDH) (2^−ΔΔCT; n = 3). (C) One representative immunoblot of legumain (proform 56 kDa, mature form 36 kDa) and GAPDH (housekeeping) in cell lysates (n = 3). (D) Quantification of the 36 kDa mature legumain immunoband (IB) intensity as arbitrary units (ARBU) relative to GAPDH in immunoblots represented in C (n = 3). (E) Legumain activity (dF/s) in cell lysates adjusted for the total protein concentration (µg/mL) (n = 6–9). (F) Secreted legumain (pg/mL) in conditioned media measured by ELISA and adjusted for the total protein concentration in the corresponding cell lysates (n = 3–5). (B,D–F) Data represent mean ± SEM. (B,D) Kruskal–Wallis test. (E,F) One-way ANOVA. * p < 0.05 vs. 0 nM 1,25(OH)₂D₃ or 25(OH)D₃. Numbers (n) represent individual biological replicates.