Fig. 5

Ligand-mediated induction of alkaline phosphatase (ALP) expression. a Dose-dependent induction of ALP gene expression in C2C12 cells. The background absorption signal of 0.08 ± 0.004 at 405 nm was subtracted from all data points. The ALP activity induced by 250 nM of BMP-2 was normalized to 100 %. b Inhibition of BMP-2-induced ALP expression by increasing concentrations of GDF-5 proteins. Half-maximal inhibitory concentrations (IC₅₀) of 70 nM and 5 nM were observed for wild-type GDF-5 (wt) and GDF-5 R57A, respectively. Expression levels (mRNA) of receptors (c) and co-receptors (d) in C2C12 (blue bars) and ATDC-5 (purple bars) cells were determined by real-time reverse transcription polymerase chain reaction. Bars represent mean values of two individual experiments. All values were normalized to HPRT gene expression. (For primer sequences and statistics see Additional file 4: Table S1)