Functional assays on different CHO, HCC1937, and HeLa cell populations. (A) Speed frequency histogram for HeLa versus HeLa–EGFP-centrin cells (means ± SEM; n = 12). X-axis values are upper bounds for each speed bin. Overexpression of EGFP-centrin did not affect the motility behavior of HeLa cells. (B) Speed frequency histogram for HCC1937 versus HCC1937–EGFP-CTD (means ± SEM; n = 8). Both cell lines showed indistinguishable motility. (C) Single-cell motility assay on human breast cancer cell lines. Graphs showing the mean speed (means ± SEM; n = 120) for different cell populations (left). HCC1937 rescued with full-length BRCA1 (HCC1937-WT) displayed a highly significant lower mean speed than their native HCC1937 counterpart. On the contrary, HCC1937 rescued with full-length ubiquitin ligase–dead BRCA1 (HCC1937-I26A) displayed a highly significant increase in mean speed over HCC1937. No change in mean speed is seen in MCF-7 cell lines expressing full-length BRCA1, but MCF-7 expressing the ubiquitin ligase–dead mutation (MCF-7–I26A) displayed a highly significant higher mean speed than their native MCF-7 counterpart. All of the mean speed differences for HCC1937 cell types rendered P < 0.01; all of the mean speed differences for MCF-7 cell types rendered P < 0.01; the mean speed difference of HCC1937-WT versus MCF-7 was not significant (P = 0.3). Speed frequency histograms for different cell populations (right). HCC1937 shows higher motility than MCF-7; expressing full-length BRCA1 in HCC1937 resulted in a left shift of the motility pattern to resemble that of MCF-7 cells. Expression of the I26A mutant in either cell type gave a right shift to increased motility, higher than the native or BRCA1-expressing cells. X-axis values are upper bounds for each speed bin.