Related Experiment Videos
Receptor-like protein-tyrosine phosphatase alpha specifically inhibits insulin-increased prolactin gene expression
K K Jacob1, J Sap, F M Stanley
1Department of Medicine, New York University Medical Center, New York, New York 10016, USA.
Abstract:
A physiologically relevant response to insulin, stimulation of prolactin promoter activity in GH4 pituitary cells, was used as an assay to study the specificity of protein-tyrosine phosphatase function. Receptor-like protein-tyrosine phosphatase alpha (RPTPalpha) blocks the effect of insulin to increase prolactin gene expression but potentiates the effects of epidermal growth factor and cAMP on prolactin promoter activity. RPTPalpha was the only protein-tyrosine phosphatase tested that did this. Thus, the effect of RPTPalpha on prolactin-chloramphenicol acetyltransferase (CAT) promoter activity is specific by two criteria. A number of potential RPTPalpha targets were ruled out by finding (a) that they are not affected or (b) that they are not on the pathway to insulin-increased prolactin-CAT activity. The negative effect of RPTPalpha on insulin activation of the prolactin promoter is not due to reduced phosphorylation or kinase activity of the insulin receptor or to reduced phosphorylation of insulin receptor substrate-1 or Shc. Inhibitor studies suggest that insulin-increased prolactin gene expression is mediated by a Ras-like GTPase but is not mitogen-activated protein kinase dependent. Experiments with inhibitors of phosphatidylinositol 3-kinase suggest that insulin-increased prolactin-CAT expression is phosphatidylinositol 3-kinase-independent. These results suggest that RPTPalpha may be a physiological regulator of insulin action.
Insights
Receptor-like protein-tyrosine phosphatase alpha (RPTPalpha) specifically regulates insulin
Area of Science:
- Cellular signaling
- Molecular endocrinology
- Gene expression regulation
Background:
- Insulin's role in cellular processes is complex and involves intricate signaling pathways.
- Protein-tyrosine phosphatases (PTPs) are key regulators of signal transduction.
- Understanding PTP specificity is crucial for deciphering cellular responses.
Purpose of the Study:
- To investigate the specific function of protein-tyrosine phosphatase alpha (RPTPalpha) in cellular signaling.
- To determine RPTPalpha's role in regulating gene expression in response to insulin.
- To elucidate the molecular mechanisms underlying RPTPalpha's effects on the prolactin promoter.
Main Methods:
- Utilized GH4 pituitary cells to assay insulin-stimulated prolactin promoter activity.
- Examined the effects of RPTPalpha on prolactin promoter activity in response to insulin, epidermal growth factor, and cAMP.
- Employed inhibitor studies targeting various signaling molecules, including Ras-like GTPase, mitogen-activated protein kinase, and phosphatidylinositol 3-kinase.
Main Results:
- RPTPalpha specifically blocked insulin's effect on prolactin gene expression.
- RPTPalpha potentiated the effects of epidermal growth factor and cAMP on prolactin promoter activity.
- The inhibitory effect of RPTPalpha on insulin signaling was independent of insulin receptor phosphorylation and phosphatidylinositol 3-kinase activity.
Conclusions:
- RPTPalpha exhibits specific regulatory functions in cellular signaling pathways.
- RPTPalpha may act as a physiological regulator of insulin action.
- The study provides insights into the specificity of protein-tyrosine phosphatase function in gene expression control.