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Fig. 7. Increase in Grb2/Sos1 complex at confluence. A, in E10 cells at 100% confluence, compared with 50% confluence, total Grb2 increased slightly (top panel), from 2409 ± 450 relative scan units to 3499 ± 667 (P = 0.08). Total Sos1 doubled, from 989 ± 379 average scan units at 50% to 1882 ± 199 at 100% (P < 0.05; second panel). Grb2/Sos1 association increased 14-fold, from 182 ± 53 to 2593 ± 91 (P < 0.01; third panel). B, in C10 cells, total Grb2 and Sos1 proteins did not change significantly with 100% confluence: 4974 ± 54 relative scan units for Grb2 at 100% versus 4061 ± 1434 for 50% (top panel) and 1480 ± 145 versus 1692 ± 1127 for Sos1 (middle panel). Grb2/Sos1 complex increased at confluence, 925 ± 219 relative scan units versus 708 ± 282 at 50% (lower panel), although this difference was not of statistical significance (P = 0.35). C, in human HPL1D cells at 100% confluence, compared with 50% confluence, total Grb2 increased slightly but significantly (1863 ± 179 to 2440 ± 91; P < 0.01; top panel). Sos1 total doubled at 100% confluence from 1430 ± 84 to 2813 ± 404 (P < 0.01; second panel). Grb2/Sos1 complex increased 6-fold at 100% confluence, from 396 ± 134 to 2284 ± 605 (P < 0.01; third panel).