Induction of translationally controlled tumor protein (TCTP) by transcriptional and post-transcriptional mechanisms

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Expression of the human TPT1 gene coding for translationally controlled tumor protein (TCTP) was investigated in Calu-6 and Cos-7 cells under the influence of 4β-phorbol 12-myristate 13-acetate (PMA), forskolin, dioxin and the heavy metals copper, nickel and cobalt. Transcriptional and post-transcriptional aspects of the mechanism were analyzed by TCTP mRNA/protein quantification, luciferase reporter gene assays depending on TPT1 promoter sequences or TCTP mRNA 5′/3′-UTRs and investigation of the interaction of RNA-binding proteins with UTRs by UV-crosslinking. PMA, forskolin, dioxin, cobalt and nickel induced TCTP expression in 24 h in both cell lines about 2.2–3.2-fold at the mRNA level and 1.6–2.2-fold at the protein level. The highest induction rate, 4.5–5.0-fold at the mRNA level and 3.5–4.0-fold at the protein level, was observed with copper. TPT1 promoter assays showed transcriptional activation by PMA, forskolin and dioxin (2.0–3.1-fold) and a 7.0–8.0-fold increase by copper, whereas cobalt and nickel had no effect. Deletion analysis revealed that copper-dependent transcriptional control was transmitted by a metal-responsive element residing in the TPT1 promoter. Post-transcriptional activation of TCTP expression was associated with the action of dioxin, nickel, cobalt (1.8–2.3-fold) and copper (2.5–3.0-fold), whereas stimulation of TCTP synthesis by copper was mediated by the TCTP mRNA 3′-UTR (3.2-fold) but not by the 5′-UTR (0.5-fold). mRNA stabilization was found to mediate these effects of cobalt and nickel. Post-transcriptional regulation was associated with qualitative and quantitative changes in the binding of specific RNA-binding proteins to UTRs.

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