Figure 2.

Control of G1 progression by varying cell shape through FN density. (A) Effects of varying FN coating density on DNA synthesis (cumulative BrdU incorporation into nuclei) and pRb hyperphosphorylation as measured in situ by nuclear extractability of hyperphosphorylated pRb (see MATERIALS AND METHODS). Error bars represent SD. (B) Western blots showing the time course of pRb hyperphosphorylation in spread cells on high FN compared with round cells on low FN. Cells were released from the lovastatin block at the time of plating; the slower-migrating band represents the hyperphosphorylated form of pRb. (C) Western blot demonstrating that decreasing the FN coating density inhibits pRb hyperphosphorylation (pRb-pp) when measured 18 h after release of lovastatin arrest in CE cells. (D) Kinetics of entry into S phase in lovastatin-synchronized cells on high FN as measured by pulse labeling with BrdU. (E) Kinetics of entry into S phase was similar in highly extended cells on high FN (3 μg/cm²; ▪) and in moderately spread cells on an intermediate FN density (100 ng/cm²; ○); highly retracted cells on low FN did not enter S phase.