Rapamycin down-regulates LDL-receptor expression independently of SREBP-2

LJ Sharpe, AJ Brown - Biochemical and biophysical research …, 2008 - Elsevier
Biochemical and biophysical research communications, 2008Elsevier
As a key regulator of cholesterol homeostasis, sterol-regulatory element binding protein-2
(SREBP-2) up-regulates expression of genes involved in cholesterol synthesis (eg, 3-
hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) Reductase) and uptake (the low density
lipoprotein (LDL)-receptor). Previously, we showed that Akt, a critical kinase in cell growth
and proliferation, contributes to SREBP-2 activation. However, the specific Akt target
involved is unknown. A potential candidate is the mammalian target of rapamycin, mTOR …
As a key regulator of cholesterol homeostasis, sterol-regulatory element binding protein-2 (SREBP-2) up-regulates expression of genes involved in cholesterol synthesis (e.g., 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) Reductase) and uptake (the low density lipoprotein (LDL)-receptor). Previously, we showed that Akt, a critical kinase in cell growth and proliferation, contributes to SREBP-2 activation. However, the specific Akt target involved is unknown. A potential candidate is the mammalian target of rapamycin, mTOR. Rapamycin can cause hyperlipidaemia clinically, and we hypothesised that this may be mediated via an effect of mTOR on SREBP-2. Herein, we found that SREBP-2 activation and HMG-CoA Reductase gene expression were unaffected by rapamycin treatment. However, LDL-receptor gene expression was decreased by rapamycin, suggesting that this may contribute to the hyperlipidaemia observed in rapamycin-treated patients. Rapamycin did not affect mRNA stability, so the decrease in LDL-receptor gene expression is likely to be occurring at the transcriptional level, although independently of SREBP-2.
Elsevier