Transforming growth factor beta targeted inactivation of cyclin E:cyclin-dependent kinase 2 (Cdk2) complexes by inhibition of Cdk2 activating kinase activity.
Proc Natl Acad Sci U S A
; 96(26): 14961-6, 1999 Dec 21.
Article
em En
| MEDLINE
| ID: mdl-10611320
ABSTRACT
Transforming growth factor beta (TGF-beta)-mediated G(1) arrest previously has been shown to specifically target inactivation of cyclin Dcyclin-dependent kinase (Cdk) 4/6 complexes. We report here that TGF-beta-treated human HepG2 hepatocellular carcinoma cells arrest in G(1), but retain continued cyclin DCdk4/6 activity and active, hypophosphorylated retinoblastoma tumor suppressor protein. Consistent with this observation, TGF-beta-treated cells failed to induce p15(INK4b), down-regulate CDC25A, or increase levels of p21(CIP1), p27(KIP1), and p57(KIP2). However, TGF-beta treatment resulted in the specific inactivation of cyclin ECdk2 complexes caused by absence of the activating Thr(160) phosphorylation on Cdk2. Whole-cell lysates from TGF-beta-treated cells showed inhibition of Cdk2 Thr(160) Cdk activating kinase (CAK) activity; however, cyclin HCdk7 activity, a previously assumed mammalian CAK, was not altered. Saccharomyces cerevisiae contains a genetically and biochemically proven CAK gene, CAK1, that encodes a monomeric 44-kDa Cak1p protein unrelated to Cdk7. Anti-Cak1p antibodies cross-reacted with a 45-kDa human protein with CAK activity that was specifically down-regulated in response to TGF-beta treatment. Taken together, these observations demonstrate that TGF-beta signaling mediates a G(1) arrest in HepG2 cells by targeting Cdk2 CAK and suggests the presence of at least two mammalian CAKs one specific for Cdk2 and one for Cdk4/6.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Fase G1
/
Fator de Crescimento Transformador beta
/
Proteínas Serina-Treonina Quinases
/
Quinases Ciclina-Dependentes
/
Ciclina E
/
Quinases relacionadas a CDC2 e CDC28
Tipo de estudo:
Prognostic_studies
Limite:
Humans
Idioma:
En
Revista:
Proc Natl Acad Sci U S A
Ano de publicação:
1999
Tipo de documento:
Article