Msx3 protein recruits histone deacetylase to down-regulate the Msx1 promoter

Msx1 promoter is known to be repressed by Msx1 protein [Shetty, Takahashi, Matsui. Iyengar and Raghow (1999) Biochem, J, 339, 751-758], We show that i n the transiently transfected C2C12 myoblasts, co-expression of Msx3 also c auses potent repression of Msx1 promoter that can be relieved by exogenous expression of cAMP-response-element-binding protein-binding protein (CBP) a nd p300 in a dose-dependent manner, Co-immunoprecipitation and Western blot analyses revealed that Msx3 interacts with CBP and p300 and this interacti on significantly decreases the histone acetyltransferase (HAT) activity of both proteins. We also discovered that Msx3-mediated repression of Msx1 pro moter is synergized by the exogenous co-expression of histone deacetylase 1 (HDAC1), Furthermore. the repression of Msx1 promoter by Msx3 could be rel ieved by treating transfected cells with trichostatin A, an inhibitor of HD AC(s). Finally, we show that Msx3 and HDAC1 can be co-immunoprecipitated in a complex that does not contain CBP and that Msx3 and HDAC1 proteins are c o-localized in the nucleus. Taken together, our results strongly suggest th at two distinct multiprotein complexes are present within the nuclei of C2C 12 cells: one containing Msx3 and HDAC(s) and another containing Msx3 and C BP and/or p300. On the basis of these results, we propose a dual mechanism of repression by Msx3 protein that involves the squelching of the HAT activ ity of coactivators, CBP and p300, and recruitment of HDAC(s).