Retinoic acid (RA) acts as an anti-proliferative and re-differentiation agent in the therapy of thyroid carcinoma but the molecular mechanisms by which RA mediates these effects are not well understood. We have investigated the effect of RA on the production and post-translational modification of the two ENO1 transcriptional products in the human follicular thyroid carcinoma cell line FTC-133. The single ENO1 transcript encodes a 48 kDa ENO1 with its unique N-terminal enolase activity and a truncated 37 kDa MBP-1 which, like ENO1, contains a C-terminal c-myc promotor-binding domain. RA treatment of FTC-133 caused a down-regulation of both ENO1 gene products. Two-dimensional gel detection and mass spectrometric analysis revealed that ENO1 existed as three separate protein spots of distinct isoelectric points (ENO1-A1-A3). Comparative 2D gel analysis of fluorescently labelled protein samples of RA treated and untreated FTC-133 (DIGE) demonstrated a selective down-regulation of ENO1-A1 which we identified as a phosphoprotein. RA caused the dephosphorylation of ENO1-A1. The down-regulation of ENO1 and MBP-1 correlated with reduced intracellular ATP levels and the down-regulation of c-Myc oncoprotein. Specific knock-down of ENO1 resulted in a marked reduction in proliferation of FTC-133. Thus, the RA-induced down-regulation and post-transcriptional modification of the ENO1/MBP-1 gene products may mediate its anti-proliferative effect by distinct molecular mechanisms, including a decrease in enolase activity and suppression of c-Myc oncogene. The glycolytic enzyme and novel RA target molecule ENO1 can facilitate both these mechanisms and may be considered a new marker in human thyroid carcinoma.
03 - 07 May 2008
European Society of Endocrinology