title: Insulin receptor kinase-associated phosphotyrosine phosphatases in hepatic endosomes: assessing the role of phosphotyrosine phosphatase-1B.
abstract: Previous work has shown that bisperoxo(1,10-phenanthroline)-oxovanadate(v) anion [bpV(phen)] induces potent insulin-mimicking effects in the rat, selectively activates the endosomal (EN) insulin receptor kinase (IRK) in liver, and markedly abolishes endosomal IRK-associated phosphotyrosine phosphatase (PTP) activity while reducing that of total ENs by approximately 30%. In this study we examined the relatively selective effect of bpv(phen) on endosomal PTP activities for the purpose of defining IRK-associated PTP(s). Using an in-gel PTP assay, we detected multiple (approximately 20) species of endosomal PTP (30 to >220 kDa), with five that were markedly inhibited after in vivo bpV(phen) administration. Using a combination of Mono Q anionic exchange chromatography and immunoblotting, we demonstrated that LAR (leukocyte common antigen-related), PTP-alpha, and PTP-1B were present in endosomal subfractions not significantly inhibited by bpv(phen). PTP-1B activity was assayed in immunoprecipitates from hepatic ENs of control and bpV(phen)-treated rats and was found to be inhibited by approximately 30% after bpv(phen) treatment. To clarify the role of PTP-1B in dephosphorylating IRK, we prepared hepatic ENs from wild-type and PTP-1B-null mice. We found that the phosphotyrosine content of IRK was similar in these two types of ENs, and that IRK dephosphorylation was not affected in ENs from PTP-1B-null mice compared with that in ENs from wild-type mice. These data suggest that LAR , PTP-alpha, and PTP-1B are not candidates for the IRK-associated PTP in hepatic ENs, and that IRK dephosphorylation in ENs may result from the concerted actions of several PTPs.
authors.affiliation: Polypeptide Hormone Laboratory, McGill Cancer Center, Montréal, Québec, Canada.
authors.forename: Chaoyang
authors.initials: C
authors.lastname: Li
authors.forename: Gerry
authors.initials: G
authors.lastname: Baquiran
authors.forename: Feng
authors.initials: F
authors.lastname: Gu
authors.forename: Michel L
authors.initials: ML
authors.lastname: Tremblay
authors.forename: Ali
authors.initials: A
authors.lastname: Fazel
authors.forename: John J M
authors.initials: JJ
authors.lastname: Bergeron
authors.forename: Barry I
authors.initials: BI
authors.lastname: Posner
mesh_terms: D000818:Animals; D011992:Endosomes / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D018345:Mice, Knockout; D009942:Organometallic Compounds / Q000494:pharmacology; D010618:Phenanthrolines / Q000494:pharmacology; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D009942:Organometallic Compounds; D010618:Phenanthrolines; C102120:bisperoxo(1,10-phenanthroline)oxovanadate(1-); D011972:Receptor, Insulin; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; C516609:Ptpn1 protein, mouse; C516610:Ptpn1 protein, rat