Papillomavirus binding factor binds to SAP30 and represses transcription via recruitment of the HDAC1 co-repressor complex

Papillomavirus binding factor, PBF, identical to the Huntington's disease binding protein 2, HDBP2, is a nuclear-cytoplasmic shuttling factor with the ability to inhibit cell growth. It has been identified by its ability to bind to GC-rich sequence elements within upstream promoter regions of certain human papillomavirus (HPV) types and of the Huntingtin protein, respectively. Here, we show that PBF acts as a repressor of HPV transcription. This repression requires the DNA-binding activity of PBF, which we mapped to two C-terminal four-amino acids motifs conserved to the so-called e-tail of certain T-cell factors. Moreover, we show that PBF directly binds to SAP30 (Sin3-associated polypeptide of 30 kDa) a component of the mSIN3A-HDAC1 complex, via amino acids 263-312. The addition of Trichostatin A, an inhibitor of HDACs, alleviated PBF-mediated repression. Thus, PBF-mediated repression of transcription involves specific DNA-binding and the recruitment of the SIN3A-HDAC1 complex.