Neuroprotection by Histone Deacetylase-7 (HDAC7) Occurs by Inhibition of c-jun Expression through a Deacetylase-independent Mechanism

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Histone deacetylase (HDAC) 7 is a member of the HDAC family of deacetylases. Although some of the HDAC proteins have been shown to regulate neuronal survival and death, whether HDAC7 has a similar role is not known. In this study, we show that HDAC7 protects neurons from apoptosis. In cerebellar granule neurons (CGNs) primed to undergo apoptosis by low potassium treatment, expression of HDAC7 protein is reduced. Reduced expression is also observed in CGNs induced to die by pharmacological inhibition of the proteasome, in cortical neurons treated with homocysteic acid, and in the striatum of R6/2 transgenic mice, a commonly used genetic model of Huntington disease. Forced expression of HDAC7 in cultured CGNs blocks low potassium-induced death, and shRNA-mediated suppression of its expression induces death in otherwise healthy neurons. HDAC7-mediated neuroprotection does not require its catalytic domain and cannot be inhibited by chemical inhibitors of HDACs. Moreover, pharmacological inhibitors of the PI3K-Akt or Raf-MEK-ERK signaling pathways or that of PKA, PKC, and Ca(2+)/calmodulin-dependent protein kinase fail to reduce neuroprotection by HDAC7. We show that stimulation of c-jun expression, an essential feature of neuronal death, is prevented by HDAC7. shRNA-mediated suppression of HDAC7 expression leads to an increase in c-jun expression. Inhibition of c-jun expression by HDAC7 is mediated at the transcriptional level by its direct association with the c-jun gene promoter. Taken together, our results indicate that HDAC7 is a neuroprotective protein acting by a mechanism that is independent of its deacetylase activity but involving the inhibition of c-jun expression.