Abstract

Several cues for cell proliferation, migration, and survival are transmitted through lipid rafts, membrane microdomains enriched in sphingolipids and cholesterol. Cells obtain cholesterol from the circulation but can also synthesize cholesterol de novo through the mevalonate/isoprenoid pathway. This pathway, however, has several branches and also produces non-sterol isoprenoids. Squalene synthase (SQS) is the enzyme that determines the switch toward sterol biosynthesis. Here we demonstrate that in prostate cancer cells SQS expression is enhanced by androgens, channeling intermediates of the mevalonate/isoprenoid pathway toward cholesterol synthesis. Interestingly, the resulting increase in de novo synthesis of cholesterol mainly affects the cholesterol content of lipid rafts, while leaving non-raft cholesterol levels unaffected. Conversely, RNA interference-mediated SQS inhibition results in a decrease of raft-associated cholesterol. These data show that SQS activity and de novo cholesterol synthesis are determinants of membrane microdomain-associated cholesterol in cancer cells. Remarkably, SQS knock down also attenuates proliferation and induces death of prostate cancer cells. Similar effects are observed when cancer cells are treated with the chemical SQS inhibitor zaragozic acid A. Importantly, although the anti-tumor effect of statins has previously been attributed to inhibition of protein isoprenylation, the present study shows that specific inhibition of the cholesterol biosynthesis branch of the mevalonate/isoprenoid pathway also induces cancer cell death. These findings significantly underscore the importance of de novo cholesterol synthesis for cancer cell biology and suggest that SQS is a potential novel target for antineoplastic intervention.

Highlights

  • As the expression of this enzyme is regulated by the cholesterol feedback mechanism and is responsive to sterol regulatory element-binding proteins (SREBPs) in other cell systems (several SREBP-binding sites (SREs) have been identified in the human Squalene synthase (SQS) promoter) [35,36,37,38], we investigated in the present work whether in prostate cancer cells SQS expression is induced by androgens and whether this regulation has an impact on the cholesterol content of raft and non-raft membrane fractions

  • We have demonstrated that androgens stimulate the expression of SQS in LNCaP prostate cancer cells, in a dose-dependent and time-dependent manner, through activation of SREBPs

  • These findings clearly demonstrate that the stimulatory effects of androgens on the expression of SQS are mediated by SREBPs, similar to previous observations for other lipogenic enzymes [32, 34]

Read more

Summary

Introduction

The resulting protein is still able to bind to SREs but is transcriptionally inactive and blocks the access of wild type endogenous SREBPs to SREs. Cotransfection of LNCaP cells with the pSQSwt-luc reporter gene (Fig. 3A) and with increasing amounts of an expression vector encoding dominant-negative SREBP almost completely abolished the stimulatory effects of androgens on SQS promoter-driven reporter expression (Fig. 3C). RNAi-mediated Inhibition of SQS Reduces Cholesterol Levels in Detergent-resistant Membrane Microdomains—To further study the role of androgen-induced cholesterol synthesis in prostate cancer cells, the SQS gene was silenced in LNCaP cells using RNA interference (RNAi) technology.

Results
Conclusion
Full Text
Published version (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