Article

Preincubation of Pituitary Tumor Cells With the Epidrugs Zebularine and Trichostatin A Are Permissive for Retinoic Acid-Augmented Expression of the BMP-4 and D2R Genes

Institute of Science and Technology in Medicine, Keele University School of Medicine, Stoke-on-Trent, Staffordshire, ST4 7QB. UK.
Endocrinology (Impact Factor: 4.64). 03/2013; 154(5). DOI: 10.1210/en.2013-1061
Source: PubMed

ABSTRACT Retinoic acid (RA) induced expression of bone morphogenetic protein (BMP-4) inhibits in vitro and in vivo cell proliferation and ACTH synthesis in corticotroph derived tumour cells. Reduced expression of BMP-4 in this adenoma subtype is associated with epigenomic silencing and similar silencing mechanisms are also associated with the RA responsive dopamine D2 receptor (D2R) in somatolactotroph cells. We now show that pre-incubation with the epidrugs, zebularine and TSA is obligate and permissive for RA induced expression of the BMP-4 and the D2R genes in pituitary tumour cells. Combined epidrug challenges are associated with marginal reduction in CpG island methylation. However, significant change to histone tail modifications toward those associated with expression-competent genes is apparent, whereas RA challenge alone or in combined incubations does not impact on these modifications. Epidrug mediated and RA augmented expression of endogenous BMP-4 increased or decreased cell proliferation and CFE in GH3 and AtT-20 pituitary tumour cells respectively, and recapitulating recent reports of challenges of these cells with exogenous ligand. The specificity of the BMP-4 mediated effects was further supported by knock-down experiments of the BMP-4 antagonist noggin (siRNA). Knock-down of noggin, in the absence and the presence of epidrugs, induced and augmented BMP-4 expression respectively. In cell proliferation assays, challenge with either epidrugs or siRNA led to significant increase in cell numbers at the 72hr time point, however, in siRNA treated cells co-incubated with epidrugs a significant increase was apparent at the 48hr time point. These studies show the potential of combined drug challenges as a treatment option, where epidrug renders silenced genes responsive to conventional therapeutic options.

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