Abstract 14600: Thiazolidinediones Regulate Internal Ribosome Entry Site Dependent Translation of Insulin-Like Growth Factor-1 Receptor in Human Aortic Smooth Muscle Cells.
The insulin-like growth factor-1 receptor (IGF-1R) stimulates vascular smooth muscle cell (SMC) proliferation, differentiation, and survival. Thiazolidinediones (TZDs), namely rosiglitazone (rosi) and pioglitazone, upregulate SMC IGF-1R. To determine mechanisms we exposed SMC to 0–20 uM rosi for 24 h which upregulated IGF-1R by 117 ± 20 % (P<0.05, n=4) without changing mRNA levels. 10 ug/mL cycloheximide abolished this effect, suggesting a translational mechanism. We have previously shown that the IGF-1R 5′-UTR contains an internal ribosome entry site (IRES), which mediates cap-independent translation. We transfected a basic bicistronic construct (pBiC) or bicistronic construct containing the IGF-1R 5′-UTR (pBiC943) between Renilla luciferase (R Luc) and Firefly luciferase (F Luc) into SMC, which were then exposed to 0–20 uM rosi for 24 h. pBiC-943 transfected SMC expressed 4.3-fold higher F/R Luc activity than pBiC transfected cells (n=6), consistent with basal IRES-dependent IGF-1R translation. However, the F/R Luc ratio was markedly increased by 10 uM rosi (12-fold increase, n=6), indicating that rosi promoted IRES dependent translation. Adenoviral overexpression of PPARγ did not mimic the TZD effect on IGF-1R expression, but downregulated IGF-1R by 62 ± 3 % (P<0.05, n=4), indicating that the TZD effect was PPARγ independent. To examine the physiological relevance of TZD upregulation of IGF-1R, we examined the effect of rosi on SMC survival and differentiation. 20 uM rosi reduced oxLDL induced apoptosis by 40 % and neutralizing antibody to IGF-1R (αIR3) counteracted this rescue, suggesting the rosi survival effect is mediated by IGF-1R. 50 ng/mL IGF-1 markedly increased smooth muscle contractile protein expression (α-smooth muscle actin (SMA); 4.2 ± 1.0 -fold, P<0.05, calponin; 2.0 ± 0.2 -fold, P<0.05), and 20 uM rosi likewise upregulated α-SMA (1.8 ± 0.1-fold, P<0.05) and calponin (1.6 ± 0.1-fold, P<0.01) expression, consistent with IGF-1R upregulation. In conclusion, TZDs upregulate IGF-1R by enhancing IRES dependent translation, contributing to SMC contractile protein expression and survival. Because the IGF-1R has a pleiotropic effects on vascular cells, our finding are important for understanding cardiovascular effects of TZDs.
- © 2010 by American Heart Association, Inc.