Dissociation of PTPase levels from their modulation of insulin receptor signal transduction.
Protein tyrosine phosphatases have been implicated in the regulation of receptor tyrosine kinase signalling pathways, including that of the insulin receptor. Here, cell density-dependent changes in PTPase expression have been exploited to investigate the relationship between cellular PTPase levels and the insulin receptor signal transduction pathway. Increasing cell density (20%, 50%, and >90%) in the rat McA-RH7777 hepatoma cell line resulted in increased protein expression of the receptor-like PTPase LAR (14-fold), and the nonreceptor PTPases PTP1B (11-fold) and SHP2 (10-fold). Each of these PTPases has previously been implicated in regulating insulin receptor signal transduction. Despite these marked increases, maximum insulin receptor autophosphorylation as well as receptor expression actually increased 2-fold. MAP kinase also increased approximately 2-fold as a function of cell density and paralleled increases in expression levels. Neither sensitivity nor maximum responsiveness to insulin were decreased at increasing cell densities as assessed by activation of PI 3-kinase. Duration of response was also unimpaired. These results suggest that expression levels of relevant PTPases are not the primary determinant in their modulation of insulin receptor kinase activity. Restricted accessibility at the molecular level or involvement of accessory proteins may be more critical parameters.
Bleyle
L A
LA
Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, NY 14642, USA.
Peng
Y
Y
Ellis
C
C
Mooney
R A
RA
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009419:Nerve Tissue Proteins; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D011972:Receptor, Insulin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516610:Ptpn1 protein, rat; C516727:Ptpn11 protein, rat; C509250:Ptpn6 protein, rat; C516774:Ptprf protein, rat; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2