Fig. 3
Cellular cooperation is driven by soluble growth supporting factors. a Analysis of PE in dependence of the assay volume for all cell lines used in Fig. 1. Four independent biological replicates are presented for all cell lines except MDA-MB231 (three replicates), and p-values were calculated by one-way Kruskal–Wallis ANOVA with the factor “volume per well”. b–d BT20 cells were cultured in standard medium supplemented with 0, 50 or 75% of conditioned medium collected from subconfluent BT20 cultures (four independent biological replicates). b PE of BT20 cells grown in different assay volumes. p-values were determined by one-way Kruskal–Wallis ANOVA with the factor “volume per well”. c Double-logarithmic presentation of clonogenic survival data from BT20 cells. Power regression lines (C = a × Sb) are superimposed, and values of the exponents b are displayed. d Visualization of the b-values as calculated in c. p-values were determined by one-way Kruskal–Wallis ANOVA with the factor “conditioned medium [%]”. e Scenario of cooperative growth behavior depending on the production of soluble growth promoting factors. f–h MDA-MB231 cells were used for the same experiments as shown for BT20 in b–d (four independent biological replicates). f PE of MDA-MB231 cells in different assay volumes. p-values were determined as in b. g Double-logarithmic presentation of clonogenic survival data from MDA-MB231 cells with power regression lines and b-values as in c. h Visualization of the b-values as calculated in g. p-values were determined as in d. i Scheme of non-cooperative cell growth independent of cell-derived factors. j Analysis of population doubling times of BT20 and MDA-MB231 cells harvested after different incubation periods. Four independent biological replicates plated in averaged technical duplicates are shown. k Schematic overview on the growth behavior of cooperatively and non-cooperatively growing cells in vitro. l SF4 values for BT20 and MDA-MB231 for different incubation periods. Calculations were performed by power regression and interpolation as in Fig. 2 and p-values were obtained by one-way Kruskal–Wallis ANOVA with the factor “11d vs. longer incubation times”