Abstract
Class II histone deacetylases (HDACs) play a role in myogenesis and inhibit transcriptional activation by myocyte enhancer factors 2. A distinct feature of class II HDACs is their ability to shuttle between the nucleus and the cytoplasm in a cell type- and signal-dependent manner. We demonstrate here that treatment with the 26 S proteosome inhibitors, MG132 and ALLN, leads to detection of ubiquitinated HDAC7 and causes accumulation of cytoplasmic HDAC7. We also show that treatment with calyculin A, a protein phosphatase inhibitor, leads to a marked increase of HDAC7 but not HDAC5. The increase in HDAC7 is accompanied by enhanced interaction between 14-3-3 proteins and HDAC7. HDAC7 mutations that prevent the interaction with 14-3-3 proteins also block calyculin A-mediated stabilization. Expression of constitutively active calcium/calmodulin-dependent kinase I stabilizes HDAC7 and causes an increased association between HDAC7 and 14-3-3. Together, our results suggest that calcium/calmodulin-dependent kinase I-mediated phosphorylation of HDAC7 acts, in part, to promote association of HDAC7 with 14-3-3 and stabilizes HDAC7.
Highlights
Acetylation and deacetylation of histone tails are critical mechanisms regulating gene expression
Inhibitors of 26 S Proteosome Stabilize Cytoplasmic HDAC7—To determine whether class II histone deacetylases (HDACs) are subject to proteosome-mediated degradation, HEK293 cells were treated with ALLN and MG132, inhibitors of the 26 S proteosome
We found that MG132 caused an accumulation of HDAC7 in the cytoplasmic but not the nuclear fraction (Fig. 3A)
Summary
Acetylation and deacetylation of histone tails are critical mechanisms regulating gene expression. Association and dissociation of sequence-specific DNA-binding transcription factors with histone acetyltransferases or HDACs in response to signaling represents an important mechanism regulating gene expression [7, 8]. Association of class II HDACs down-regulates myocyte enhancer factor 2-mediated transcription activity and thereby controls myoblast differentiation (16, 19 –22). We proposed that CaMK I-mediated phosphorylation on these serine residues promotes association of class II HDACs with cytoplasmic 14-3-3 proteins [12]. We demonstrate that cytoplasmic HDAC7 is a target of ubiquitin-mediated proteolysis. Increased phosphorylation leads to a marked increase of endogenous and transfected HDAC7 This phosphorylation-dependent activity requires the N-terminal conserved serine residues of HDAC7. Our data suggest a concerted regulation of HDAC7 activity by phosphorylation-mediated nuclear export and ubiquitin-regulated proteolysis
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