Mevalonate inhibits acid sphingomyelinase activity, increases sphingomyelin levels and inhibits cell proliferation of HepG2 and Caco-2 cells

Ying Chen,Rui-Dong Duan,Shu-Chang Xu

doi:10.1186/s12944-015-0137-8

Ying Chen, Rui-Dong Duan + Show 1 more

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https://doi.org/10.1186/s12944-015-0137-8

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Abstract

BackgroundSphingomyelin (SM) and cholesterol are two types of lipid closely related biophysically. Treating the cells with exogenous sphingomyelinase (SMase) induces trafficking of cholesterol from membrane to intracellular pools and inhibition of cholesterol synthesis. In the present work, we address a question whether increased cholesterol synthesis affects hydrolysis of SM by endogenous SMases.MethodsBoth HepG2 and Caco-2 cells were incubated with mevalonate. The SMase activity was determined and its mRNA examined by qPCR. The cellular levels of cholesterol, SM, and phosphatidylcholine (PC) were determined and cell proliferation rate assayed.ResultsWe found that mevalonate dose-dependently decreased acid but not neutral SMase activity in both HepG2 and Caco-2 cells with HepG2 cells being more sensitive to mevalonate. Kinetic examination in HepG2 cells revealed that acid SMase activity was increasing with cell proliferation, and such an increase was reversed by mevalonate treatment. Acid SMase mRNA was not significantly decreased and Western blot showed signs of proteolysis of acid SMase by mevalonate. After mevalonate treatment, the levels of cholesterol were significantly increased associated with increases in SM and PC. The cell growth was retarded by mevalonate and the effect was more obvious in HepG2 cells than in Caco-2 cells.ConclusionMevalonate can trigger a mechanism to enhance SM levels by inhibition of acid SMase. The effect may ensure the coordinate changes of SM and cholesterol in the cells. Mevalonate also affects cell growth with mechanism required further characterization.

Highlights

Cholesterol and sphingomyelin (SM) are two important lipid constituents of mammalian cell membranes and are co-localized in lysosomes, endosomes, intestinal vesicles, plasma lipoproteins, and fat milk globular membrane
The present study addresses a question whether increased cholesterol synthesis induced by providing exogenous mevalonate can affect SM and SM hydrolytic enzymes in HepG2 liver cells and Caco-2 intestinal cells
Mevalonate reduces acid SMase activity in HepG2 and Caco2 cells After incubating HepG2 and Caco-2 cells with mevalonate, we found that the activities of acid SMase were decreased (Fig. 1)

Summary

Introduction

Cholesterol and sphingomyelin (SM) are two important lipid constituents of mammalian cell membranes and are co-localized in lysosomes, endosomes, intestinal vesicles, plasma lipoproteins, and fat milk globular membrane. Mevalonate pathway generates non-sterol products which can affect gene translation and cell proliferation via mechanism related to post-transcriptional regulation [11, 12]. SM is degraded mainly by acid and neutral SMases, two types of ubiquitous enzymes in mammalian cells. Acid SMase (SMPD1) is a lysosomal enzyme that degrades SM internalized or transported in the intracellular vesicles [13], playing important roles in regulating cellular SM levels. The best studied neutral SMase is nSMase 2 that plays important roles in SM metabolism, cell signaling, tumorigenesis and bone homeostasis.

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