Protein Kinase D1 Phosphorylates HDAC7 and Induces Its Nuclear Export after T-cell Receptor Activation

HDAC7, a class II histone deacetylase that is highly expressed in thymocytes, inhibits both transcription of the orphan steroid nuclear receptor Nur77 and induction of apoptosis in response to activation of the T-cell receptor (TCR). Here, we report that HDAC7 is exported to the cytoplasm by a calcium-independent signaling pathway after TCR activation. Protein kinase D1 (PKD1) was activated after TCR engagement, interacted with HDAC7, and phosphorylated three serines (Ser155, Ser318, and Ser448) at its N terminus, leading to its export from the nucleus. Mutation of Ser155, Ser318, and Ser448 blocked the nucleocytoplasmic shuttling of HDAC7 in response to TCR activation, as did overexpression of a kinase-inactive form of PKD1. Consistent with the regulatory role of HDAC7 in Nur77 expression, PKD1 activation led to the transcriptional activation of Nur77 via myocyte enhancer factor 2-binding sites in its promoter. In a mouse model of negative selection, PKD1 was activated during thymocyte activation. These observations indicate that PKD1 regulates the expression of Nur77 during thymocyte activation at least in part by phosphorylating HDAC7.