E2F-1
AG490, a member of the tryphostin family of protein kinase inhibitors, repressed G(0)-G(1)
traverse in BALB/c-3T3 cells. While the early induction of STAT activity was
repressed by AG490, extracellular signal-regulated kinase (ERK) activation was unaffected and a pattern of
gene expression suggested that cells exited G(0) in
the presence of the inhibitor. Although AG490 did not alter the induction of cyclin D1 protein, neither cyclin
D1- nor cyclin D3-associated kinase
activity was observed in growth-inhibited cells. Surprisingly, p130 was
partially phosphorylated, and E2F3A protein was
expressed in mitogen-stimulated AG490-treated cells
despite the lack of cyclin D-associated kinase activity. These data suggest that AG490 inhibits a
cellular pathway required for mid-G(0)-G(1) traverse
that is located after the induction of early processes potentially mediated by
E2F (although independent of cyclin D-associated kinase activity) but before the late G(1) increase in
E2F-dependent transcription. Infection of AG490-treated cells with an E2F-1
adenovirus caused the induction of cyclin A, but
could not overcome the drug-induced cell cycle arrest that was coincident with
the repression of cyclin-dependent kinase 2 (cdk2)-associated kinase
activation. We conclude that cdk2-associated kinase
activity is modulated by a cellular process repressed by AG490. Furthermore, this
cdk2-associated kinase activity is required for G(0)-G(1) traverse in some role other than the regulation of
E2F-dependent transcription.
PMID: 14985461 [PubMed - in process]