Cross-talk between signal transducer and activator of transcription (Stat5) and thyroid hormone receptor-β 1 (TRβ1) signaling pathways

Abstract

PRL and T3 are involved in antagonistic regulations during various developmental processes in vertebrate species. We have studied cross-talk between transcription factors activated by these signaling pathways, i.e. signal transducer and activator of transcription 5 (Stat5) and thyroid hormone receptor β1 (TRβ1). Liganded TRβ1 in the presence of its heteredimeric partner, retinoid X receptor γ (RXRγ), inhibited the PRL-induced Stat5a- and Stat5b-dependent reporter gene expression by up to 60%. This T3-inhibitory effect studied on Star5 activity was partly reversed by overexpression of a TRβ1 dominant negative variant mutated within its nuclear localization signal (TR2A). We next showed that TRβ1 and TR2A in the presence of RXRγ increased and decreased, respectively, Stat5 localization into the nucleus regardless of hormonal stimulation. Thus, our data suggest that TRβ1 can be associated with Stat5 in the cytoplasm and may be involved in Stat5 nuclear translocation. In PRL-treated cells over-expressing TRβ1/RXRγ, both Stat5 and TRβ1 were coimmunoprecipitated, indicating physical association of the two transcription factors. In these cells, addition of T3 with ovine (o)PRL decreased the amounts of total and tyrosine-phosphorylated Stat5 in the cytoplasm compared with oPRL-treated cells. In the nucleus, no clear difference was observed on Stat5 DNA-binding after treatment with PRL and T3 vs. PRL alone in TRβ1/RXRγ transfected cells. However, antibodies directed against TRβ1 lowered Stat5-DNA binding and addition of the deacetylase inhibitor trichostatin A (TSA) relieved T3 inhibition on Stat5 transcriptional activity. Thus, we postulated that the negative cross-talk between TR and Stat5 on target genes could involve histone deacetylase recruitment by liganded TRβ1.