High insulin levels do not influence PC-1 gene expression and protein content in human muscle tissue and hepatoma cells.
BACKGROUND
To verify whether insulin levels influence PC-1 tissue content, we studied PC-1 gene expression and protein content in skeletal muscle of patients with insulinoma, a model of primary hyperinsulinemia. Data were compared with those obtained in matched insulin sensitive or resistant healthy subjects. In addition, the effect of high insulin concentration on PC-1 protein content was studied in HepG2 cells.


METHODS
The following measurements were performed: insulin sensitivity by euglycemic clamp; PC-1 protein content and insulin receptor autophosphorylation by specific ELISAs; PC-1 gene expression by competitive polymerase chain reaction (PCR); phosphatidyl-inositol-3 kinase by immunoprecipitation and thin layer chromatography; glycogen synthesis by (14)C-glucose incorporation.


RESULTS
Muscle PC-1 content was similar in the insulinoma patients and in insulin sensitive controls but higher (p<0.01) in insulin resistant controls (21.9+/-4.6 ng/mg protein, 23.8+/-3.9, 48.0+/-8.7, respectively). PC-1 protein content was inversely correlated with insulin sensitivity (r=-0.5, p<0.015) but with neither plasma insulin nor glucose levels. PC-1 protein content was correlated with PC-1 gene expression (r=0.53, p<0.05, n=14). Exposure to high insulin (100 nmol/l for 16 h) caused a significant (p<0.05-0.01) impairment of insulin receptor autophosphorylation, phosphatidyl-inositol-3 kinase activity and glycogen synthesis, but not of PC-1 protein content (114+/-3 vs 102+/-14 ng/mg protein) in HepG2 cells.


CONCLUSIONS
These findings suggest that chronic high insulin levels do not influence PC-1 expression.
Frittitta
L
L
Institute of Internal Medicine, Endocrine and Metabolic Diseases, University of Catania, Garibaldi Hospital, Catania, Italy. segmeint@mbox.unict.it
Sbraccia
P
P
Costanzo
B V
BV
Tassi
V
V
D'Adamo
M
M
Spampinato
D
D
Ercolino
T
T
Purrello
F
F
Tamburrano
G
G
Vigneri
R
R
Trischitta
V
V
D006528:Carcinoma, Hepatocellular; D005786:Gene Expression Regulation; D015309:Glucose Clamp Technique; D006003:Glycogen / Q000096:biosynthesis; D006801:Humans; D007328:Insulin / Q000502:physiology*; D007333:Insulin Resistance; D007340:Insulinoma / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008113:Liver Neoplasms; D008562:Membrane Glycoproteins / Q000235:genetics*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases; D010766:Phosphorylation; D011755:Pyrophosphatases / Q000235:genetics; D011972:Receptor, Insulin / Q000378:metabolism; D012016:Reference Values; D014407:Tumor Cells, Cultured
D007328:Insulin; D008562:Membrane Glycoproteins; D006003:Glycogen; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases