title: Amyloid beta-peptide alters the distribution of early endosomes and inhibits phosphorylation of Akt in the presence of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT).
abstract: Amyloid beta-peptide (Abeta) effectively inhibits the cellular reduction activity of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) in a variety of cultured cells. Although the inhibitory activity is widely used for the estimation of the biological activity of Abeta, the cellular mechanism is unclear. In the present study, we examined the effect of Abeta on the morphology of early endosomes, in which MTT is accumulated as MTT formazan after cellular reduction. We found that Abeta1-40 alters the distribution of Rab5- and early endosomal auto-antigen 1-positive early endosomes in the presence of MTT in HeLa cells, which are susceptible to the Abeta1-40-induced inhibition of cellular MTT reduction. To obtain a clue to the molecular mechanism, we determined whether Abeta1-40 affects the signal cascade of the phosphatidylinositol-3-OH kinase (PI-3K) pathway that is involved in early endosomal trafficking. MTT induced phosphorylation of Akt and mitogen-activated protein kinase. Abeta1-40 suppressed the PI-3K-dependent Akt phosphorylation but not the mitogen-activated protein kinase phosphorylation. Thus, Abeta seems to modulate early endosomal trafficking via inhibition of the PI-3K pathway in the presence of MTT. Modulation of early endosomal trafficking appears to affect the cellular metabolism of MTT, causing suppression of cellular MTT reduction by Abeta. These findings may help clarify the mechanism of the cytotoxicity of Abeta.
authors.affiliation: Neuroscience and Immunology Research Laboratories, Sankyo Co., Ltd., 1-2-58, Hiromachi, Shinagawa-ku, Tokyo 140-8710, Japan.
authors.forename: Takekazu
authors.initials: T
authors.lastname: Kubo
authors.forename: Satoko
authors.initials: S
authors.lastname: Nishimura
authors.forename: Tomiichiro
authors.initials: T
authors.lastname: Oda
mesh_terms: D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000906:Antibodies / Q000378:metabolism; D015415:Biomarkers; D002867:Chromones / Q000378:metabolism; D004396:Coloring Agents / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000378:metabolism; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000494:pharmacology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt; D013778:Tetrazolium Salts / Q000378:metabolism*; D013844:Thiazoles / Q000378:metabolism*; D033921:Vesicular Transport Proteins; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D000906:Antibodies; D015415:Biomarkers; D002867:Chromones; D004396:Coloring Agents; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D009025:Morpholines; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D013778:Tetrazolium Salts; D013844:Thiazoles; D033921:Vesicular Transport Proteins; C078592:amyloid beta-protein (1-40); C093846:early endosome antigen 1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020696:rab5 GTP-Binding Proteins; C022616:thiazolyl blue