c-Abl induces stabilization of histone deacetylase 1 (HDAC1) in a kinase activity-dependent manner

c-Abl is a non-receptor-type tyrosine kinase that regulates various cellular events, including cell proliferation, differentiation, and apoptosis, through phosphorylation of cytoplasmic and nuclear targets. Although we showed that c-Abl induces histone deacetylation, the molecular mechanisms of this phenomenon are largely unknown. Here, we analyzed the effect of c-Abl on the expression of histone deacetylase 1 (HDAC1), because c-Abl was shown to be involved in maintenance of nuclear protein levels of HDAC1. Co-transfection of HDAC1 with c-Abl increased the levels of HDAC1 protein in a kinase activity-dependent manner without affecting its mRNA levels. Treatment with the proteasome inhibitor MG132 increased protein levels of HDAC1 in cells transfected with HDAC1 but not in cells co-transfected with HDAC1 and c-Abl. Among class I HDACs, knockdown of endogenous c-Abl preferentially suppressed endogenous protein levels of HDAC1, suggesting that c-Abl stabilizes HDAC1 protein by inhibiting its proteasomal degradation. Subcellular fractionation showed that the stabilization of HDAC1 by c-Abl occurred in the nucleus. Despite the fact that HDAC1 was phosphorylated by co-expression with c-Abl, stabilization of HDAC1 by c-Abl was not affected by mutations in its sites phosphorylated by c-Abl. Co-expression with HDAC1 and nuclear-targeted c-Abl did not affect HDAC1 stabilization. Therefore, these results suggest that c-Abl induces HDAC1 stabilization possibly through phosphorylation of a cytoplasmic target that is involved in proteasomal degradation of HDAC1.