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A more recent version of this article appeared on February 1, 2008
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Submitted on June 29, 2007
Revised on November 12, 2007
Accepted on November 20, 2007
*Dipartimento di Scienze e Tecnologie Biomediche, Sezione di Biologia and MATI Center of Excellence Università di Udine, 33100 Udine, Italy;
IRBM/Merck Research Laboratories Rome, 00040 Pomezia, Italy
Monitoring Editor: Karsten Weis
Different signal-regulated serine/threonine kinases phosphorylate class II HDACs to promote nuclear export, cytosolic accumulation, and activation of gene transcription. However, little is known about mechanisms operating in the opposite direction, which, possibly through phosphatases, should promote class II HDACs nuclear entry and subsequent gene repression. Here we show that HDAC4 forms a complex with the PP2A holoenzyme C
, A
, B/PR55
. In vitro and in vivo binding studies demonstrate that the N-terminus of HDAC4 interacts with the catalytic subunit of PP2A. HDAC4 is dephosphorylated by PP2A and experiments using okadaic acid (OA) or RNAi have revealed that PP2A controls HDAC4 nuclear import. Moreover, we identified serine 298 as a putative phosphorylation site important for HDAC4 nuclear import. The HDAC4 mutant mimicking phosphorylation of serine 298 is defective in nuclear import. Mutation of serine 298 to alanine partially rescues the defect in HDAC4 nuclear import observed in cells with down-regulated PP2A. These observations suggest that PP2A, via the dephosphorylation of multiple serines including the 14–3-3 binding sites and serine 298, controls HDAC4 nuclear import.