Abstract
Intracellular calcium is one of the important signals that initiates the myogenic program. The calcium-activated phosphatase calcineurin is necessary for the nuclear import of the nuclear factor of activated T cell (NFAT) family members, which interact with zinc finger GATA transcription factors. Whereas GATA-6 plays a role in the maintenance of the differentiated phenotype in vascular smooth muscle cells (VSMCs), it is unknown whether the calcineurin pathway is associated with GATA-6 and plays a role in the differentiation of VSMCs. The smooth muscle-myosin heavy chain (Sm-MHC) gene is a downstream target of GATA-6, and provides a highly specific marker for differentiated VSMCs. Using immunoprecipitation Western blotting, we showed that NFATc1 interacted with GATA-6. Consistent with this, NFATc1 further potentiated GATA-6-activated Sm-MHC transcription. Induction of VSMCs to the quiescent phenotype caused nuclear translocation of NFATc1. In differentiated VSMCs, blockage of calcineurin down-regulated the amount of GATA-6-DNA binding as well as the expression of Sm-MHC and its transcriptional activity. These findings demonstrate that the calcineurin pathway is associated with GATA-6 and is required for the maintenance of the differentiated phenotype in VSMCs.