Akt acutely activates the cholesterogenic transcription factor SREBP-2

Abstract

Akt is an essential protein kinase for cell growth, proliferation, and survival. Perturbed Akt regulation is associated with a number of human diseases, such as cancer and diabetes. Recently, evidence has emerged that Akt is involved in the regulation of the sterol-regulatory element binding proteins, which are master transcriptional regulators of lipid metabolism. This offers a means by which synthesis of new membrane can be coordinated with cell growth and proliferation. However, the link between Akt and sterol-regulatory element binding protein-2, the major isoform participating in cholesterol regulation, is relatively unexplored. In the present study, we employed insulin-like growth factor-1 as an inducer of Akt signalling, and showed that it increased sterol-regulatory element binding protein-2 activation acutely (within 1h). This insulin-like growth factor-1-induced sterol-regulatory element binding protein-2 activation was blunted when Akt was inhibited pharmacologically or molecularly with small interfering RNA. Furthermore, we employed a rapalog heterodimerisation system to specifically and rapidly activate Akt, and found that sterol-regulatory element binding protein-2 activation was increased in response to Akt activation. Together, this study provides compelling evidence that Akt contributes to the acute regulation of cholesterol metabolism through activating sterol-regulatory element binding protein-2.

The terminal enzymes of cholesterol synthesis, DHCR24 and DHCR7, interact physically and functionally

“…CHO-7 cells overexpressing human DHCR24 [CHO-DHCR24-V5 ( 19 )], or the pcDNA5/FRT empty vector (EV) [CHO-EV ( 21 )], were previously generated in-house. The CHO-DHCR24 Y471S-V5 stable cell line was generated for this study using the Flp-In system, as described in ( 21 ). Protein expression was screened by Western blotting.…”

“…The Flp-In-CHO cell-line (for stable-cell generation) was generated in CHO-7 cells ( 21 ). CHO-7 cells overexpressing human DHCR24 [CHO-DHCR24-V5 ( 19 )], or the pcDNA5/FRT empty vector (EV) [CHO-EV ( 21 )], were previously generated in-house.…”

Controlling Cholesterol Synthesis beyond 3-Hydroxy-3-methylglutaryl-CoA Reductase (HMGCR)

“…34). Growth factors involving signaling via the androgen receptor or Akt can also up-regulate cholesterogenic genes, but this occurs indirectly, through activation of SREBP-2 (35,36).…”

Signaling regulates activity of DHCR24, the final enzyme in cholesterol synthesis

“…The empty vector stable cell-line (CHO-EV) was prepared as described ( 42 ), and the human wild-type DHCR24 overexpressing cell-line (CHO-DHCR24-WT) was prepared as described ( 30 ).…”