Insulin-like growth factor-1 increases endothelin receptor A levels and action in cultured rat aortic smooth muscle cells.
Insulin is known to cause an increase in endothelin-1 (ET-1) receptors in vascular smooth muscle cells (SMCs), but the effect of insulin-like growth factor 1 (IGF-1) on ET-1 receptor expression is not known. We therefore carried out the present study to determine the effect of IGF-1 on the binding of ET-1 to, and ET type A receptor (ETAR) expression and ET-1-induced 3H-thymidine incorporation in, vascular SMCs. In serum-free medium, IGF-1 treatment increased the binding of 125I-ET-1 to SMC cell surface ET receptors from a specific binding of 20.1%+/-3.1% per mg of protein in control cells to 45.1%+/-8.6% per mg of protein in cells treated with IGF-1 (10 nM). The effect of IGF-1 was dose-related, with a significant effect (1.4-fold) being seen at 1 nM. The minimal time for IGF-1 treatment to be effective was 30 min and the maximal effect was reached at 6 h. Immunoblotting analysis showed that ETAR expression in IGF-1-treated cells was increased by 1.7-fold compared to controls. Levels of ETAR mRNA measured by the RT-PCR method and Northern blotting were also increased by 2-fold in IGF-1-treated SMCs. These effects of IGF-1 were abolished by cycloheximide or genistein. Finally, ET-1-stimulated thymidine uptake and cell proliferation were enhanced by IGF-1 treatment, with a maximal increase of 3.2-fold compared to controls. In conclusion, in vascular SMCs, IGF-1 increases the expression of the ET-1 receptor in a dose- and time-related manner. This effect is associated with increased thymidine uptake and involves tyrosine kinase activation and new protein synthesis. These findings support the role of IGF-1 in the development of atherosclerotic, hypertensive, and diabetic vascular complications.
Kwok
Ching Fai
CF
Department of Medicine, Division of Endocrinology and Metabolism, Taipei Veterans General Hospital, Taiwan. cfkwok@vghtpe.gov.tw
Juan
Chi-Chang
CC
Shih
Kuang-Chung
KC
Hwu
Chii-Min
CM
Jap
Tjin-Shing
TS
Ho
Low-Tone
LT
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D017931:DNA Primers; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013936:Thymidine / Q000378:metabolism
D017931:DNA Primers; D012333:RNA, Messenger; D044022:Receptor, Endothelin A; D007334:Insulin-Like Growth Factor I; D013936:Thymidine