Fitting the model of ER-dependent gene expression to multi-level experimental data. (A) The equilibrium model of ER binding with the hormone was fitted against the data on equilibrium binding of recombinant hERα with labelled estradiol (17β -[6,7 -3H(N)] estradiol), registered at four different concentrations of hERα: 0.3 (black square); 1.2 (blue triangle); 7 (red circle); and 13 (green diamond) nM. The data were taken from . ER_b is the concentration of ER binding sites, bound with hormone; Ht -total concentration of labelled estradiol. (B) and (C): The equilibrium model was used to fit the data on competitive binding of ligands with ER in the presence of labelled 17β-estradiol. The competitive ligands were: unlabelled 17β-estradiol (B) and tamoxifen (C). The experimental data were taken from . (D) The steady state protein expression (p) was fitted to the data on reporter gene expression (ALP) in HEK293/hERα cell line treated with tamoxifen (black line) and tamoxifen+0.5 nM 17β-estradiol (blue line); data taken from . Points correspond to experimental data, lines – to theoretical curves. More details on the fitting procedure and model calibration can be found in the Additional File 2.