Epigenetic modulation of the protein kinase A RII alpha (PRKAR2A) gene by histone deacetylases 1 and 2 in human smooth muscle cells

Recently we reported that the expression of the protein kinase A (PKA) regulatory subunit RII alpha is dynamically regulated in human smooth muscle cells of the uterus. We showed that expression levels of mRNA/protein were substantially increased during pregnancy and decreased upon labour, changes that were mirrored by particulate type II PKA activity. This implied an important role for RII alpha in maintaining uterine quiescence during pregnancy. Consequently the purpose of the present study was to identify potential mechanisms by which expression of the RII alpha gene was regulated in this tissue. We indicate here that the three SpI-III (GC) binding domains within the proximal promoter region of the human RII alpha gene may play important roles in modulating expression of the gene in human myometrial cells. We show that all three GC binding domains are involved in binding Sp1, Sp3, histone deacetylase (HDACs) 1/2 and RbAp48 transcriptional complexes. The functional significance of these binding domains was further analysed employing in vitro luciferase reporter assays with full-length/truncated RII alpha promoter constructs. Importantly we show that treatment of primary human myometrial cell cultures with the general class I/II HDAC inhibitor trichostatin A results in an increase in mRNA/protein levels. Moreover the increase in mRNA levels appeared to be preceded by an increase in aH3, PolIIa, Sp3 and HDAC 2 binding to the three SpI-III (GC) binding sites within the RII alpha promoter. These results enable us to provide a model whereby RII alpha expression is epigenetically regulated in human myometrial smooth muscle cells by histone deacetylase(s) activity within the GC-rich proximal promoter region of the gene.