Figure 5.

Integrin-mediated activation of JNK is required for progression through the G1 phase of the cell cycle. NIH-3T3 fibroblasts were transiently transfected with 1 μg of vector encoding β-galactosidase alone or in combination with the indicated amounts of plasmids encoding CD2-FAK, CD2-FAK K454R, GST-CAS (wild-type), GST-SD-CAS (substrate region deleted), v-Crk, SH3⁻ v-Crk, GST-Wt MKK4 (wild-type), GST-Dn MKK4, Dn-Jun (Δ3-122), or Dn-RAS (N17). After synchronization in G0 by serum deprivation, the cells transfected only with the β-galactosidase plasmid were plated on coverslips coated with poly-l-lysine (PL, white bar) or fibronectin (Fn, black bar), while those cotransfected with vectors encoding wild-type and constitutively active proteins (stippled bars) or corresponding dominant-negative versions (gray bars) were plated only on fibronectin. After 16 h of incubation in defined medium supplemented with PDGF and BrdU, the cells were fixed and stained with anti-BrdU mAb. The number of transfected cells entering S phase was evaluated as described in Materials and Methods. Under these conditions, none of the cells plated on fibronectin in the absence of PDGF enter into S phase. The diagram shows the mean value and standard deviation from triplicate samples.