(The FASEB Journal. 2008;22:lb299)
© 2008 FASEB
Regulation of (di-hydro) ceramide synthase 1
Priya Sridevi1,
Hannah Alexander1,
Elad Laviad3,
Mark Hannink2,
Anthony Futerman3 and
Stephen Alexander1
1 Biological Sciences
2 Biochemistry, Univ. Of Missouri, Columbia, MO
3 Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel
ABSTRACT
The mammalian (di-hydro) ceramide synthases (CerS) are a family of 6 genes, previously referred to as longevity assurance (LASS) genes based on their function in yeast. CerS1 catalyzes the synthesis of C18:0-ceramide, which is known to have important roles in cell signaling, inflammation and apoptosis. However the mechanism of action and regulation of CerS1 is not well understood. Previously we have shown that over-expression of CerS1 increases cellular sensitivity to the chemotherapeutic drug cisplatin and other stresses. We also showed that CerS1 and not CerS5 translocates from the ER to the Golgi apparatus following stress. CerS1 levels are tightly regulated and endogenous CerS1 is undetectable in most tissues except for the brain. Here we study the mechanisms that regulate CerS1 levels. In the presence of cycloheximide (CHX), CerS1 protein level rapidly decreases, indicating that it has a short half-life. Cytotoxic stresses such as cisplatin, doxorubicin and UV cause a further down-regulation of CerS1. CerS1 is basally ubiquitinated and the observed down-regulation involves ubiquitination and proteasome-dependent degradation. Though an inactive CerS1 mutant has a short half-life similar to wild type CerS1, it does not show stress-induced down-regulation. This shows that stress-induced down-regulation of CerS1 requires CerS1 activity. Inhibition of the p38-MAP kinase prevented CerS1 ubiquitination. We also show that protein kinase C (PKC) activation stabilized CerS1, while PKC inhibition de-stabilized CerS1. These studies for the first time demonstrate the regulation of a protein in the sphingolipid pathway by ubiquitination-mediated proteolysis in a PKC and p38-dependent manner. This research is supported by NIGMS; US-Israel Binational Science Foundation.
