A role for cell cycle-regulated phosphorylation in Groucho-mediated transcriptional repression.
Transcriptional corepressors of the Groucho/transducin-like Enhancer of split (Gro/TLE) family are involved in a variety of cell differentiation mechanisms in both invertebrates and vertebrates. They become recruited to specific promoter regions by forming complexes with a number of different DNA-binding proteins thereby contributing to the regulation of multiple genes. To understand how the functions of Gro/TLE proteins are regulated, it was asked whether their ability to mediate transcriptional repression might be controlled by cell cycle-dependent phosphorylation events. It is shown here that activation of p34(cdc2) kinase (cdc2) with okadaic acid is correlated with hyperphosphorylation of Gro/TLEs. Moreover, pharmacological inhibition of cdc2 activity results in Gro/TLE dephosphorylation. In agreement with these findings, a purified cdc2-cyclin B complex can directly phosphorylate Gro/TLEs in vitro. Two separate Gro/TLE domains, the CcN and SP regions, contain sequences that are phosphorylated by cdc2. Deletion of these sequences is correlated with loss of Gro/TLE phosphorylation by cdc2 in vitro and okadaic acid-induced Gro/TLE hyperphosphorylation in vivo. In addition, Gro/TLEs are phosphorylated during the G(2)/M phase of the cell cycle, and this is correlated with a decreased nuclear interaction. Finally, the transcription repression ability of Gro/TLEs is enhanced by pharmacological inhibition of cdc2. Taken together, these results demonstrate that Gro/TLE proteins are phosphorylated as a function of the cell cycle and implicate phosphorylation events occurring during mitosis in the negative regulation of Gro/TLE activity.
Nuthall
Hugh N
HN
Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
Joachim
Kerline
K
Palaparti
Anuradha
A
Stifani
Stefano
S
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila; D004742:Enhancer Elements, Genetic; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008938:Mitosis; D019319:Okadaic Acid / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D051792:Basic Helix-Loop-Helix Proteins; D016203:CDC2 Protein Kinase; D004268:DNA-Binding Proteins; D019319:Okadaic Acid; D010710:Phosphates; D011994:Recombinant Proteins; D012097:Repressor Proteins; C091023:gro protein, Drosophila