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Vol. 19, Issue 2, 655-667, February 2008

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PP2A Regulates HDAC4 Nuclear Import

Gabriela Paroni^*, Nadia Cernotta^*, Claudio Dello Russo, Paola Gallinari, Michele Pallaoro, Carmela Foti^*, Fabio Talamo, Laura Orsatti, Christian Steinkühler, and Claudio Brancolini^*

*Dipartimento di Scienze e Tecnologie Biomediche, Sezione di Biologia and MATI Center of Excellence, Universita' di Udine, 33100 Udine, Italy; and IRBM/Merck Research Laboratories Rome, 00040 Pomezia, Italy

Submitted June 29, 2007; Revised November 12, 2007; Accepted November 20, 2007
Monitoring Editor: Karsten Weis

Different signal-regulated serine/threonine kinases phosphorylate class II histone deacetylases (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 or RNA interference 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.

Address correspondence to: Claudio Brancolini (cbrancolini{at}makek.dstb.uniud.it)