Myosin phosphatase dephosphorylates HDAC7, controls its nucleocytoplasmic shuttling, and inhibits apoptosis in thymocytes

The repressive activity of histone deacetylase 7 (HDAC7), a class IIa HDAC expressed in CD4(+)CD8(+) double-positive thymocytes, is regulated by its nucleocytoplasmic shuttling. In resting thymocytes, HDAC7 is nuclear and functions as a transcriptional repressor. After T-cell receptor (TCR) activation, the serine/threonine kinase PKD1 phosphorylates HDAC7, resulting in its nuclear export and the derepression of its target genes. Here, we identify protein phosphatase 1 beta (PP1 beta) and myosin phosphatase targeting subunit 1 (MYPT1), two components of the myosin phosphatase complex, as HDAC7-associated proteins in thymocytes. Myosin phosphatase dephosphorylates HDAC7 and promotes its nuclear localization, leading to the repression of the HDAC7 target, Nur77, and the inhibition of apoptosis in CD4(+)CD8(+) thymocytes.