Abstract
TRAIL/Apo2L (tumor necrosis factor-related apoptosis-inducing ligand) is a multifunctional protein regulating homeostasis of the immune system, infection, autoimmune diseases, and apoptosis. However, its function in normal, nontransformed tissues is not clear. Here we show that TRAIL increases vascular smooth muscle cell (VSMC) proliferation in vitro, effects that can be blocked with neutralizing antibodies to TRAIL receptors DR4 and DcR1. In aortocoronary saphenous vein bypass grafts in vivo, TRAIL co-localizes with VSMC, proliferating cell nuclear antigen, and insulin-like growth factor type 1 receptor (IGF1R) expression but not active caspase-3. TRAIL is required for serum-inducible IGF1R expression, and antisense IGF1R inhibits TRAIL-induced VSMC proliferation. At 1 ng/ml, TRAIL stimulates IGF1R mRNA expression greater than insulin-like growth factor-1 and also activates the IGF1R promoter 7-fold. TRAIL-inducible IGF1R expression requires NF-kappaB activation. Consistent with this, ammonium pyrrolidine dithiocarbamate, a pharmacological inhibitor of NF-kappaB, blocks TRAIL-induced IGF1R expression, and p65 overexpression increases IGF1R protein levels. In addition, NF-kappaB binds a novel TRAIL-responsive element on the IGF1R promoter. Our findings suggest that the biological functions of TRAIL in VSMC extend beyond its role in promoting apoptosis. Thus, TRAIL may play an important role in atherosclerosis by regulating IGF1R expression in VSMC in an NF-kappaB-dependent manner.
Highlights
Our findings suggest that the biological functions of TRAIL in vascular smooth muscle cell (VSMC) extend beyond its role in promoting apoptosis
This study suggests that TRAIL may protect VSMC, it is not clear if the increase in VSMC content was a direct effect of TRAIL or due to changes in other cell types
Human plaque-derived VSMC have reduced insulin-like growth factor type 1 receptor (IGF1R) expression and a subsequent defect in IGF1R-dependent survival [21]. This may be potentially detrimental in advanced atherosclerosis, given that apoptosis of VSMC can lead to plaque vulnerability and rupture [22], processes that can precipitate myocardial infarction and sudden death
Summary
The following day, cells were starved for 24 h followed by the addition of human recombinant TRAIL (R&D Systems) for a further 24 h in serum-free medium. For antisense (AS) and sense (S) assays targeting the IGF1R [24], human VSMC were starved in serum-free medium for 6 h prior to transfection with AS or S using FuGENE6. The following day, a second transfection with AS and S was performed in either TRAIL-containing medium (1 ng/ml, for proliferation assays) or DMEM containing 20% fetal calf serum (for protein expression). Flow Cytometry for Annexin V/Propidium Iodide (PI) Staining—At 60 –70% confluence, human VSMC were starved for 24 h followed by the addition of TRAIL at the indicated concentrations for a further 24 h. Recombinant protein or nuclear extract was incubated at mRNA expression /β-actin Total cell counts. Comparisons between three or more unpaired groups were made using analysis of variance. p Ͻ 0.05 was considered significant
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
