J. Biol. Chem., Vol. 262, Issue 13, 6069-6073, May, 1987
Taurine enhances low density lipoprotein binding. Internalization and degradation by cultured Hep G2 cells
ZF Stephan, S Lindsey and KC Hayes
To evaluate the impact of taurine on hepatic cholesterol catabolism low
density lipoprotein (LDL) binding, internalization and degradation were
measured in cultured Hep G2 cells. Preincubation of cells with 0.1-10 mM
taurine for 24 h stimulated LDL receptor activity by as much as 100%. Only
the high affinity LDL receptor activity (specific) was increased by taurine
preincubation, whereas the low affinity receptor activity (nonspecific)
remained unchanged. Scatchard analysis of the binding data revealed that
taurine doubled the number of LDL receptors without affecting receptor
affinity. Taurine-enhanced LDL receptor activity was most pronounced when
LDL concentrations exceeded 100 micrograms/ml, but was noted at taurine
concentrations as low as 0.1 mM (plasma level). Interestingly, taurine had
no effect on LDL receptor activity when it was added simultaneously with
125I-LDL to Hep G2 cells, or when non-bile acid-producing human skin
fibroblasts were tested. Stimulation of LDL receptor activity was also
obtained with 10 mM cysteine, a taurine precursor, but not with glycine.
Increased cellular concentrations of taurine and cysteine were associated
with an elevated rate of bile acid synthesis and a reduced cellular free
cholesterol concentration. The data suggest that taurine enhanced LDL
receptor activity by sparing cysteine, a known sulfhydryl group donor and
stimulator of 7 alpha-hydroxylase activity, and that the latter stimulated
bile acid production leading to increased utilization of cellular free
cholesterol and enhanced LDL uptake.