Abstract
Protein kinase B (AKT) is a serine/threonine kinase that functions as an important downstream effector of phosphoinositide 3-kinase. We have recently shown that MK-2206 and triciribine, two highly selective AKT inhibitors increase the level of low density lipoprotein receptor (LDLR) mRNA which leads to increased amount of cell-surface LDLRs. However, whereas MK-2206 induces transcription of the LDLR gene, triciribine stabilizes LDLR mRNA, raising the possibility that the two inhibitors may actually affect other kinases than AKT. In this study, we aimed to ascertain the role of AKT in regulation of LDLR mRNA expression by examining the effect of five additional AKT inhibitors on LDLR mRNA levels. Here we show that in cultured HepG2 cells, AKT inhibitors ARQ-092, AKT inhibitor VIII, perifosine, AT7867 and CCT128930 increase LDLR mRNA levels by inducing the activity of LDLR promoter. CCT128930 also increased the stability of LDLR mRNA. To study the role of AKT isoforms on LDLR mRNA levels, we examined the effect of siRNA-mediated knockdown of AKT1 or AKT2 on LDLR promoter activity and LDLR mRNA stability. Whereas knockdown of either AKT1 or AKT2 led to upregulation of LDLR promoter activity, only knockdown of AKT2 had a stabilizing effect on LDLR mRNA. Taken together, these results provide strong evidence for involvement of AKT in regulation of LDLR mRNA expression, and point towards the AKT isoform specificity for upregulation of LDLR mRNA expression.
Highlights
Low density lipoprotein (LDL) is the major cholesterol-carrying lipoprotein in humans, making up approximately 70% of circulating cholesterol [1]
As a first step towards ascertaining whether inhibition of AKT is responsible for induction of LDL receptor (LDLR) by MK-2206 or triciribine, we examined the effect of additional AKT inhibitors on the LDLR levels
We set out to examine the expression of LDLR protein levels in HepG2 cells that were exposed to ARQ-092, AKT inhibitor VIII, perifosine, AT7867 or CCT128930 for 14 h
Summary
Low density lipoprotein (LDL) is the major cholesterol-carrying lipoprotein in humans, making up approximately 70% of circulating cholesterol [1]. Mutations in genes that cause a reduction in LDLR levels or function lead to elevated plasma LDL-cholesterol levels which are associated with an increased risk of cardiovascular disease [1, 2]. Consistent with the essential role of the LDLR in regulation of plasma LDL-cholesterol levels, therapies aimed at increasing LDLR levels, such. Expression of LDLR is tightly regulated at multiple levels to ensure normal cellular function. The expression of LDLR gene is mainly regulated by sterol regulatory element-binding protein-2 (SREBP-2) [4]. The active SREBP-2 binds to its cognate sterol regulatory element-1 (SRE-1) in the LDLR promoter and induces LDLR expression [7, 8]. LDLR mRNA is relatively labile, with a half-life of approximately 2 hours [9], and the stability of LDLR mRNA is dictated by regulatory sequences in the 3’untranslated region (3’UTR) that serve as binding sites for mRNA stabilizing and destabilizing trans-regulatory proteins [10, 11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
