(A, B) Correlation analysis of actin and calcium dynamics in MCF-7 cells undergoing CaAR. (A) Temporal shift between half-maximal decay of calcium (Ca), actin maximum at nuclear periphery (ER) and actin minimum at the cell cortex (Co). (B) Correlation between Ca and ER (red, Pearson correlation coefficient, r = 0.924), Ca and Co (green, r = 0.840) and between ER and Co (black, r = 0.880). Dotted lines: y = x. (C) Stochastic model for actin competition. Filaments at the cortex (green) and ER (red) are represented by arrows (head: barbed end, circle: capped end). Total length of cortical (LC) and ER (LER) actin is indicated. Monomer pool is given by LG. Relevant parameters: Rates of severing (rs per length l), capping (rc), nucleation (rn), velocities of elongation (v+) and depolymerization (v-). See Supplementary material for details of the model. (D) Evolution of F-actin concentration at ER (red) and cortex (green) generated by the model using a simple competition scenario (dotted lines) or including calcium-activated depolymerization of actin (full lines). All simulations were run using the indicated Ca2+ curve (black) as input. (E) Average intensity curves of Lifeact-mCherry at ER (red) and cell cortex (green) of HeLa KO cells expressing wildtype or WH2 mutant GFP-INF2-CAAX (3L: L976A, L977A, L986A). Dotted red and green lines indicate SEM. (F) Effect of different depolymerization rates on maximal actin change at cortex (green) and ER (red). Shown are predictions from simulations (left) and experimental data comparing wildtype and 3L-INF2 expressing HeLa cells (data points, mean and SD). (G) As in (F) but showing the effects of varying depolymerization rate on the time until cortical minimum or ER-maximum is reached.