Acute cholesterol depletion leads to net loss of the organic osmolyte taurine in Ehrlich Lettré tumor cells.
In mammalian cells, the organic osmolyte taurine is accumulated by the Na-dependent taurine transporter TauT and released though the volume- and DIDS-sensitive organic anion channel. Incubating Ehrlich Lettré tumor cells with methyl-β-cyclodextrin (5 mM, 1 h) reduces the total cholesterol pool to 60±5% of the control value. Electron spin resonance data indicate a concomitant disruption of cholesterol-rich micro-domains. Active taurine uptake, cellular taurine content, and cell volume are reduced by 50, 20 and 20% compared to control values, respectively, whereas the passive taurine release is increased 4.5-fold under isotonic conditions following cholesterol depletion. However, taurine release under isotonic conditions is insensitive to DIDS and inhibitors of the volume-regulated anion channel. Uptake and release of meAIB are similarly affected following cholesterol depletion. Kinetic analysis reveals that cholesterol depletion increases TauT's affinity toward taurine but reduces its maximal transport capacity. Cholesterol depletion has no impact on TauT regulation by protein kinases A and C. Phospholipase A2 activity, which is required for the activation of volume-sensitive organic anion channel (VSOAC), is increased under isotonic and hypotonic conditions following cholesterol depletion, whereas taurine release under hypotonic conditions is reduced following cholesterol depletion. Hence, acute cholesterol depletion of Ehrlich Lettré cells leads to reduced TauT and VSOAC activities and at the same time increases the release of organic osmolytes via a leak pathway different from the volume-sensitive pathways for amino acids and anions.
Villumsen
Kasper Rømer
KR
Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, The August Krogh Building, Universitetsparken 13, 2100, Copenhagen Ø, Denmark.
Duelund
Lars
L
Lambert
Ian Henry
IH
D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism* / Q000473:pathology*; D002784:Cholesterol / Q000172:deficiency* / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D051379:Mice; D009995:Osmosis; D054467:Phospholipases A2 / Q000378:metabolism; D013654:Taurine / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D047392:beta-Cyclodextrins / Q000494:pharmacology; D000099247:Taurine Transporters
D002784:Cholesterol; D007473:Ion Channels; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D054467:Phospholipases A2; D013654:Taurine; D047392:beta-Cyclodextrins; D000099247:Taurine Transporters; C108732:methyl-beta-cyclodextrin