Transforming growth factor beta facilitates beta-TrCP-mediated degradation of Cdc25A in a Smad3-dependent manner.
Ubiquitin-dependent degradation of Cdc25A is a major mechanism for damage-induced S-phase checkpoint. Two ubiquitin ligases, the Skp1-cullin-beta-TrCP (SCFbeta-TrCP) complex and the anaphase-promoting complex (APCCdh1), are involved in Cdc25A degradation. Here we demonstrate that the transforming growth factor beta (TGF-beta)-Smad3 pathway promotes SCF(beta-TrCP)-mediated Cdc25A ubiquitination. Cells treated with TGF-beta, as well ... as cells transfected with Smad3 or a constitutively active type I TGF-beta receptor, exhibit increased ubiquitination and markedly shortened half-lives of Cdc25A. Furthermore, Cdc25A is stabilized in cells transfected with Smad3 small interfering RNA (siRNA) and cells from Smad3-null mice. TGF-beta-induced ubiquitination is associated with Cdc25A phosphorylation at the beta-TrCP docking site (DS82G motif) and physical association of Cdc25A with Smad3 and beta-TrCP. Cdc25A mutant proteins deficient in DS82G phosphorylation are resistant to TGF-beta-Smad3-induced degradation, whereas a Cdc25A mutant protein defective in APCCdh1 recognition undergoes efficient degradation. Smad3 siRNA inhibits beta-TrCP-Cdc25A interaction and Cdc25A degradation in response to TGF-beta. beta-TrCP2 siRNA also inhibits Smad3-induced Cdc25A degradation. In contrast, Cdh1 siRNA had no effect on Cdc25A down-regulation by Smad3. These data suggest that Smad3 plays a key role in the regulation of Cdc25A ubiquitination by SCFbeta-TrCP and that Cdc25A stabilization observed in various cancers could be associated with defects in the TGF-beta-Smad3 pathway.
Mesh Terms:
Animals, Cell Line, Tumor, DNA-Binding Proteins, Half-Life, Humans, Immunoprecipitation, Mice, Mutation, Neoplasms, Phosphorylation, Proteasome Endopeptidase Complex, RNA, Small Interfering, Receptors, Transforming Growth Factor beta, Smad3 Protein, Trans-Activators, Transfection, Transforming Growth Factor beta, Ubiquitin, beta-Transducin Repeat-Containing Proteins, cdc25 Phosphatases
Animals, Cell Line, Tumor, DNA-Binding Proteins, Half-Life, Humans, Immunoprecipitation, Mice, Mutation, Neoplasms, Phosphorylation, Proteasome Endopeptidase Complex, RNA, Small Interfering, Receptors, Transforming Growth Factor beta, Smad3 Protein, Trans-Activators, Transfection, Transforming Growth Factor beta, Ubiquitin, beta-Transducin Repeat-Containing Proteins, cdc25 Phosphatases
Mol. Cell. Biol.
Date: Apr. 01, 2005
PubMed ID: 15798217
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