Immunocytochemical detection of phosphatidylinositol 3-kinase activation by insulin and leptin.
Intracellular signaling mediated by phosphatidylinositol 3-kinase (PI3K) is important for a number of cellular processes and is stimulated by a variety of hormones, including insulin and leptin. A histochemical method for assessment of PI3K signaling would be an important advance in identifying specific cells in histologically complex organs that are regulated by growth factors and peptide hormones. However, current methods for detecting PI3K activity require either homogenization of the tissue or cells or the ability to transfect probes that bind to phosphatidylinositol 3,4,5 trisphosphate (PIP3), the reaction product of PI3K catalysis. Here we report the validation of an immunocytochemical method to detect changes in PI3K activity, using a recently developed monoclonal antibody to PIP3, in paraformaldehyde-fixed bovine aortic endothelial cells (BAECs) in culture and in hepatocytes of intact rat liver. Treatment with either insulin or leptin increased BAEC PIP3 immunoreactivity, and these effects were blocked by pretreatment with PI3K inhibitors. Furthermore, infusion of insulin into the hepatic portal vein of fasted rats caused an increase of PIP3 immunostaining in hepatocytes that was associated with increased serine phosphorylation of the downstream signaling molecule protein kinase B/Akt (PKB/Akt). We conclude that immunocytochemical PIP3 staining can detect changes in PI3K activation induced by insulin and leptin in cell culture and intact liver.
Niswender
Kevin D
KD
Division of Metabolism, Endocrinology and Nutrition, Seattle, Washington, USA. kniswend@u.washington.edu
Gallis
Byron
B
Blevins
James E
JE
Corson
Marshall A
MA
Schwartz
Michael W
MW
Baskin
Denis G
DG
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation; D022781:Hepatocytes / Q000378:metabolism; D007150:Immunohistochemistry; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000378:metabolism; D013997:Time Factors
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; C526299:Irs2 protein, rat; C494920:Akt1 protein, rat