Expression and function of receptors for insulin-like growth factor-I and insulin in human coronary artery smooth muscle cells.
OBJECTIVE
Hyperinsulinaemia and insulin resistance, as well as low IGF-I, have been implicated in the pathogenesis of cardiovascular disease. Little is known about direct effects of IGF-I and insulin on human coronary artery smooth muscle cells (HCASMCs). Our aim was to characterise the expression and function of IGF-I receptor (IGF-IR) and insulin receptor (IR) in HCASMCs.


METHODS
Cultured HCASMCs were used. mRNA expression was measured by quantitative real-time RT-PCR analysis. Receptor proteins, phosphorylation of beta-subunits and the presence of hybrid IR/IGF-IR were analysed by immunoprecipitation and western blotting. DNA synthesis and glucose metabolism were assessed using [3H]thymidine incorporation and D-[U-14C]glucose accumulation respectively.


RESULTS
The mRNA expression of IGF-IR was approximately eight-fold higher than that of IR in HCASMCs. The presence of IGF-IR and IR could be demonstrated by immunoprecipitation and western blot analysis. Phosphorylation of the IGF-IR beta-subunit was obtained by IGF-I at 10(-10)-10(-8) mol/l and insulin at 10(-8) mol/l. Insulin and IGF-I at 10(-10)-10(-9) mol/l phosphorylated the IR beta-subunit. When immunoprecipitated with monoclonal anti-IR alpha-subunit or IGF-IR alpha-subunit antibodies, we found bands in slightly different positions, suggesting the presence of hybrid IR/IGF-IR. IGF-I at 10(-9)-10(-8) mol/l significantly stimulated [3H]thymidine incorporation and at a concentration of 10(-9)-10(-7) mol/l also D-[U-14C]glucose accumulation in HCASMCs. Insulin at 10(-9)-10(-7) mol/l had no effect on DNA synthesis, but increased glucose accumulation at 10(-7) mol/l.


CONCLUSIONS
Our study provides experimental evidence that IGF-IR and possibly hybrid IR/IGF-IR play a role in HCASMCs.
Chisalita
S I
SI
Division of Cell Biology, Department of Biomedicine and Surgery, Faculty of Health Sciences, Linköping University, S-58185 Linköping, Sweden.
Arnqvist
H J
HJ
D015153:Blotting, Western; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism*; D018076:DNA, Complementary / Q000096:biosynthesis; D005947:Glucose / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D010766:Phosphorylation; D012313:RNA / Q000096:biosynthesis; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis* / Q000235:genetics; D011972:Receptor, Insulin / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013936:Thymidine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D018076:DNA, Complementary; D014443:Tyrosine; D012313:RNA; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D005947:Glucose; D013936:Thymidine