title: Inhibition of autophagy and multiple steps in asialoglycoprotein endocytosis by inhibitors of tyrosine protein kinases (tyrphostins).
abstract: In isolated rat hepatocytes, several tyrosine protein kinase inhibitors (tyrphostins) reduced the autophagic sequestration of electroinjected [3H]raffinose by 40-75% at doses that did not significantly affect cellular ATP levels or plasma membrane integrity. Tyrphostin 46 specifically inhibited autophagy, whereas tyrphostins 1, 25 and 51 also suppressed the receptor-mediated endocytic uptake of 125I-tyramine-cellobiose-asialoorosomucoid, 125I-TC-AOM, by 20-30% and its degradation by 70-90%. Tyrphostins 1 and 51, and the microtubule inhibitor vinblastine, inhibited an early endocytic step (endosome maturation/multivesiculation?), causing accumulation of endocytosed 125I-TC-AOM in a recycling compartment that corresponded to light endosomes (1.10-1.11 g/ml) in sucrose density gradients. In the electron microscope, these endosomes could be recognized as small, peripheral endocytic vesicles and tubules accumulating endocytosed AOM-gold. The serine/threonine protein phosphatase inhibitor okadaic acid inhibited an intermediate endocytic step (detachment of multivesicular endosomes from the tubulovesicular network?), causing accumulation of 125I-TC-AOM in a recycling compartment corresponding to light endosomes (1.10-1.11 g/ml), but with a multivesicular rather than a tubulovesicular morphology. Tyrphostin 25 inhibited endocytosis at a late step (endosome-lysosome fusion?), causing accumulation of 125I-TC-AOM in a non-recycling compartment corresponding to dense, multivesicular endosomes (1.14 g/ml) that had probably detached from the light endosomal network.
authors.affiliation: Department of Tissue Culture, Norwegian Radium Hospital, Oslo.
authors.forename: I
authors.initials: I
authors.lastname: Holen
authors.forename: P E
authors.initials: PE
authors.lastname: Strømhaug
authors.forename: P B
authors.initials: PB
authors.lastname: Gordon
authors.forename: M
authors.initials: M
authors.lastname: Fengsrud
authors.forename: T O
authors.initials: TO
authors.lastname: Berg
authors.forename: P O
authors.initials: PO
authors.lastname: Seglen
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001212:Asialoglycoproteins / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology*; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000502:physiology / Q000648:ultrastructure; D004988:Ethers, Cyclic / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D008247:Lysosomes / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D019319:Okadaic Acid; D015388:Organelles / Q000502:physiology* / Q000648:ultrastructure; D014176:Protein Biosynthesis / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D014617:Vacuoles / Q000502:physiology / Q000648:ultrastructure; D014638:Vanadates / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D001212:Asialoglycoproteins; D004988:Ethers, Cyclic; D019319:Okadaic Acid; D014638:Vanadates; D014747:Vinblastine; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases