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Fig. 7. Model summarizing cell cycle regulation from mitosis to S phase in N2A and CHO cells. Normal cell cycle progression from mitosis into S phase in the presence of growth factors involves cell spreading, stress fiber formation and focal adhesion assembly and is characterized by both FAK and MAPK signaling and the expression of cyclins D and E (condition d). Growth factor depletion after mitosis induces inhibition of MAPK signaling, the loss of cyclin D and the subsequent prevention of cyclin E expression, leading to growth arrest in G1 (condition e). Post-mitotic transfer to suspension or to a non-supportive substratum that allows only non-specific reattachment and no cell spreading also induces cell cycle arrest, via inhibition of FAK signaling and prevention of cyclin E induction (conditions a and b, respectively). However, cells that are released on a permissive substratum (i.e. supportive for integrin signaling and cell spreading) but are not spread because of improper cytoskeletal reorganization do not arrest in G1 despite a progressive loss of cyclin D levels, presumably because pre-existing cell cycle regulators activate the cell cycle machinery sufficiently early after mitosis (condition c).
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