Toshiaki Miyazaki

Identification of XAF1 as an antagonist of XIAP anti-Caspase activity.

The inhibitors of apoptosis (IAPs) suppress apoptosis through the inhibition of the caspase cascade and thus are key proteins in the control of cell death. Here we have isolated the protein XIAP-associated factor 1 (XAF1) on the basis of its ability to bind XIAP, a member of the IAP family. XIAP suppresses caspase activation and cell death in vitro, and XAF1 antagonizes these XIAP activities. Expression of XAF1 triggers a redistribution of XIAP from the cytosol to the nucleus. XAF1 is ubiquitously expressed in normal tissues, but is present at low or undetectable levels in many different cancer cell lines. Loss of control over apoptotic signalling is now recognized as a critical event in the development of cancer. Our results indicate that XAF1 may be important in mediating the apoptosis resistance of cancer cells.

c-Myb acetylation at the carboxyl-terminal conserved domain by transcriptional co-activator p300

Transcription factor c-Myb plays important roles in cell survival and differentiation in immature hematopoietic cells. Here we demonstrate that c-Myb is acetylated at the carboxyl-terminal conserved domain by histone acetyltransferase p300 both in vitro and in vivo. The acetylation sites in vivo have been located at the lysine residues of the conserved domain (K471, K480, K485) by the use of the mutant Myb (Myb-KAmut), in which all three lysine residues are substituted into alanine. Electrophoretic mobility shift assay reveals that Myb-KAmut shows higher DNA binding activity than wild type c-Myb and that acetylation of c-Myb in vitro by p300 causes dramatic increase in DNA binding activity. Accordingly, transactivation activity of both mim-1 and CD34 promoters by Myb-KAmut is higher than that driven by wild type c-Myb. Furthermore, the bromodomain of p300, in addition to the histone acetyltransferase (HAT) domain, is required for effective acetylation of c-Myb, and hGCN5 is revealed to be a factor acetyltransferase for c-Myb in vitro. We present a new manner of post-translational modification of the c-Myb protein and the potential significance of the acetylation in c-Myb.