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Decreased autophosphorylation of EGF receptor in insulin-deficient diabetic rats
1Research Division, Joslin Diabetes Center, Boston, Massachusetts 02115.
Abstract:
We have previously reported that despite an increase in receptor concentration, there is a decrease in autophosphorylation and tyrosine kinase activity of the insulin receptor in insulin-deficient diabetic rats. To determine if other tyrosine kinases might be altered, we have studied the epidermal growth factor (EGF) receptor kinase in wheat germ agglutinin-purified, Triton X-100-solubilized liver membranes from streptozotocin (STZ)-induced diabetic rats and the insulin-deficient BB rat. We find that autophosphorylation of EGF receptor is decreased in proportion to the severity of the diabetic state in STZ rats with a maximal decrease of 67% (P less than 0.01). A similar decrease in autophosphorylation was observed in diabetic BB rats that was partially normalized by insulin treatment. Separation of tryptic phosphopeptides by reverse-phase high-performance liquid chromatography revealed a decrease in labeling at all sites of autophosphorylation. A parallel decrease in EGF receptor phosphorylation was also found by immunoblotting with an anti-phosphotyrosine antibody. EGF receptor concentration, determined by Scatchard analysis of 125I-labeled EGF binding, was decreased by 39% in the STZ rat (P less than 0.05) and 27% in the diabetic BB rat (not significant). Thus autophosphorylation of EGF receptor, like that of the insulin receptor, is decreased in insulin-deficient rat liver. In the case of EGF receptor, this is due in part to a decrease in receptor number and in part to a decrease in the specific activity of the kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
In insulin-deficient diabetes, both insulin and epidermal growth factor (EGF) receptor autophosphorylation decrease. This reduction in EGF receptor activity is due to lower receptor numbers and reduced kinase specific activity.
Area of Science:
- Biochemistry
- Molecular Biology
- Endocrinology
Background:
- Insulin receptor activity decreases in diabetic rats.
- Investigating other tyrosine kinases in diabetes is crucial.
Purpose of the Study:
- To examine epidermal growth factor (EGF) receptor kinase activity in insulin-deficient diabetic rats.
- To determine if EGF receptor autophosphorylation is altered in diabetes.
Main Methods:
- Studied EGF receptor kinase in liver membranes from streptozotocin (STZ)-induced and BB diabetic rats.
- Assessed autophosphorylation, phosphopeptide labeling, and receptor concentration.
- Used wheat germ agglutinin purification, Triton X-100 solubilization, and Scatchard analysis.
Main Results:
- EGF receptor autophosphorylation decreased significantly (up to 67%) in STZ rats, correlating with diabetic severity.
- Similar decreases were seen in BB rats, partially reversed by insulin.
- Receptor concentration decreased by 39% in STZ rats and 27% in BB rats.
- Reduced labeling at all autophosphorylation sites and decreased specific activity were observed.
Conclusions:
- Autophosphorylation of EGF receptor is diminished in insulin-deficient rat liver.
- This decrease results from both reduced receptor number and impaired kinase specific activity.
- Findings parallel those of the insulin receptor, suggesting broader kinase dysfunction in diabetes.