Subcellular targeting domains of sphingomyelin synthase 1 and 2.

Calvin Yeang,Xian-Cheng Jiang,Tingbo Ding,William J Chirico

doi:10.1186/1743-7075-8-89

Calvin Yeang, Xian-Cheng Jiang + Show 2 more

Open Access

https://doi.org/10.1186/1743-7075-8-89

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Abstract

Sphingomyelin synthase (SMS) sits at the crossroads of sphingomyelin (SM), ceramide, diacylglycerol (DAG) metabolism. It utilizes ceramide and phosphatidylcholine as substrates to produce SM and DAG, thereby regulating lipid messengers which play a role in cell survival and apoptosis. Furthermore, its product SM has been implicated in atherogenic processes such as retention of lipoproteins in the blood vessel intima. There are two mammalian sphingomyelin synthases: SMS1 and SMS2. SMS1 is found exclusively in the Golgi at steady state, whereas SMS2 exists in the Golgi and plasma membrane. Conventional motifs responsible for protein targeting to the plasma membrane or Golgi are either not present in, or unique to, SMS1 and SMS2. In this study, we examined how SMS1 and SMS2 achieve their respective subcellular localization patterns. Brefeldin A treatment prevented SMS1 and SMS2 from exiting the ER, demonstrating that they transit through the classical secretory pathway. We created truncations and chimeras of SMS1 and SMS2 to define their targeting signals. We found that SMS1 contains a C-terminal Golgi targeting signal and that SMS2 contains a C-terminal plasma membrane targeting signal.

Highlights

Sphingomyelin synthase is the last enzyme required for de novo synthesis of sphingomyelin (SM)
GFP-SMS1 was co-localized with trans-Golgi network peptide 46 (TGN46) to the Golgi apparatus (Figure 1A) while GFP-SMS2 was localized to the Golgi apparatus and plasma membrane (Figure 1B)
Brefeldin A inhibits the sorting of SMS1 and SMS2 The fungal metabolite brefeldin A (BFA) inhibits anterograde vesicular transport from the endoplasmic reticulum (ER) to Golgi [9] and thereby leads to accumulation of proteins which transit through the classical secretory pathway in the ER

Summary

Introduction

Sphingomyelin synthase is the last enzyme required for de novo synthesis of sphingomyelin (SM). SMSr is highly homologous to SMS1 and SMS2, it does not have SM synthase activity [1]. Instead, it regulates cellular ceramide levels through synthesis of ceramide phosphoethanolamine [2]. SM, in addition to functioning as a structural component in biological membranes, preferentially interacts with cholesterol to form specialized membrane microdomains or “lipid rafts” [3]. Both ceramide and DAG have been implicated in numerous cell functions including growth, differentiation, signal transduction, proliferation, and apoptosis [4,5].

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