Poly(ADP-ribose) polymerase is a B-MYB coactivator

B-MYB is implicated in cell growth control, differentiation, and cancer and belongs to the MYB family of nuclear transcription factors. Evidence exist s that cellular proteins bind directly to B-MYB, and it has been hypothesiz ed that B-MYB transcriptional activity may be modulated by specific cofacto rs. In an attempt to isolate proteins that interact with the B-MYB DNA-bind ing domain, a modular domain that has the potential to mediate protein-prot ein interaction, we performed pull-down experiments with a glutathione S-tr ansferase-B-MYB protein and mammalian protein extracts. We isolated a 110-k Da protein associated endogenously with B-MYB in the nuclei of HL60 cells. Microsequence analysis and immunoprecipitation experiments determined that the bound protein was poly(ADP-ribose) polymerase (PARP). Transient transfe ction assays showed that PARP enhanced B-MYB transactivation and that PARP enzymatic activity is not required for B-MYB-dependent transactivation. The se results suggest that PARP, as a transcriptional cofactor of a potentiall y oncogenic protein, may play a role in growth control and cancer.