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Ceramide in stem cell differentiation and embryo development: novel functions of a topological cell-signaling lipid and the concept of ceramide compartments.

Bieberich E - J Lipids (2010)

Bottom Line: In the last two decades, the view on the function of ceramide as a sole metabolic precursor for other sphingolipids has completely changed.A plethora of studies has shown that ceramide is an important lipid cell-signaling factor regulating apoptosis in a variety of cell types.Recent studies suggest that ceramide is a critical cell-signaling factor for stem cell differentiation and cell polarity, two processes at the core of embryo development.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Neurobiology, Institute of Molecular Medicine and Genetics, School of Medicine, Medical College of Georgia, 1120 15th Street Room CA4012, Augusta, GA 30912, USA.

ABSTRACT
In the last two decades, the view on the function of ceramide as a sole metabolic precursor for other sphingolipids has completely changed. A plethora of studies has shown that ceramide is an important lipid cell-signaling factor regulating apoptosis in a variety of cell types. With the advent of new stem cell technologies and knockout mice for specific steps in ceramide biosynthesis, this view is about to change again. Recent studies suggest that ceramide is a critical cell-signaling factor for stem cell differentiation and cell polarity, two processes at the core of embryo development. This paper discusses studies on ceramide using in vitro differentiated stem cells, embryo cultures, and knockout mice with the goal of linking specific developmental stages to exciting and novel functions of this lipid. Particular attention is devoted to the concept of ceramide as a topological cell-signaling lipid: a lipid that forms distinct structures (membrane domains and vesicles termed "sphingosome"), which confines ceramide-induced cell signaling pathways to localized and even polarized compartments.

No MeSH data available.


Related in: MedlinePlus

Structure of aPKC and the “flipside” model of ceramide activity. (a) In aPKC (Figure shows PKCζ), the N-terminal (regulatory) and C-terminal (catalytic) moieties are connected by a hinge region. The N-terminus contains a pseudosubstrate (PS) motif and a PB1 domain. The PB1 domain is associated with the polarity protein Par6 that itself binds to Cdc42. The hinge region contains a C1b domain that has been suggested to be associated with ceramide and is a putative binding site for PAR-4. The C-terminal moiety contains the catalytic domain and several phosphorylation sites involved in activation of the enzyme. Most recently, we have constructed a dominant negative mutant from the C-terminus of aPKC (C20ζ-GFP) that binds to ceramide. Therefore, aPKC may contain two distinct ceramide-binding sites. In the inactive state of aPKC, the N-terminal PS motif “folds back” onto the C-terminal catalytic domain and blocks its access to protein substrates. We have proposed that binding to ceramide “opens up” aPKC and primes its activation by phosphorylation or inhibition by PAR-4 (Flipside model of ceramide activity). (b) For the activation reaction, ceramide binding to aPKC is followed by its association with Par6 and Cdc42. PIP2 or 3 may participate in aPKC activation and subcellular translocation by binding to active (GTP-associated) Cdc42 in this complex. This ceramide-aPKC polarity complex (CAP-PC) may inhibit GSK-3β and control cell polarity, process formation/migration, or ciliogenesis as described in Figure 3. In the presence of increased levels of active PAR-4, ceramide-associated aPKC binds to PAR-4 and forms a ceramide-aPKC apoptosis complex (CAP-AC). This complex inhibits aPKC and prevents activation of its downstream targets, NF-κB and Akt. We have proposed that this leads to activation of Bax/Bad and induction of apoptosis.
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fig2: Structure of aPKC and the “flipside” model of ceramide activity. (a) In aPKC (Figure shows PKCζ), the N-terminal (regulatory) and C-terminal (catalytic) moieties are connected by a hinge region. The N-terminus contains a pseudosubstrate (PS) motif and a PB1 domain. The PB1 domain is associated with the polarity protein Par6 that itself binds to Cdc42. The hinge region contains a C1b domain that has been suggested to be associated with ceramide and is a putative binding site for PAR-4. The C-terminal moiety contains the catalytic domain and several phosphorylation sites involved in activation of the enzyme. Most recently, we have constructed a dominant negative mutant from the C-terminus of aPKC (C20ζ-GFP) that binds to ceramide. Therefore, aPKC may contain two distinct ceramide-binding sites. In the inactive state of aPKC, the N-terminal PS motif “folds back” onto the C-terminal catalytic domain and blocks its access to protein substrates. We have proposed that binding to ceramide “opens up” aPKC and primes its activation by phosphorylation or inhibition by PAR-4 (Flipside model of ceramide activity). (b) For the activation reaction, ceramide binding to aPKC is followed by its association with Par6 and Cdc42. PIP2 or 3 may participate in aPKC activation and subcellular translocation by binding to active (GTP-associated) Cdc42 in this complex. This ceramide-aPKC polarity complex (CAP-PC) may inhibit GSK-3β and control cell polarity, process formation/migration, or ciliogenesis as described in Figure 3. In the presence of increased levels of active PAR-4, ceramide-associated aPKC binds to PAR-4 and forms a ceramide-aPKC apoptosis complex (CAP-AC). This complex inhibits aPKC and prevents activation of its downstream targets, NF-κB and Akt. We have proposed that this leads to activation of Bax/Bad and induction of apoptosis.

Mentions: S18 is a special kind of ceramide analog designed and synthesized in our laboratory [18, 19]. By maintaining the polar (serine-derived) head group of ceramide, and at the same time, enhancing the water solubility of the lipophilic portion, we obtained a water-soluble, but still lipophilic, structural analog of ceramide (Figure 1). The extensive characterization of S18 showed that it incorporates into cell membranes and activates atypical PKC (aPKC), which was also found for ceramide [18–21]. Moreover, ceramide and S18 induce the formation of aPKC-associated complexes with polarity proteins such as Par6 and the small Rho-type GTPase Cdc42 (Figures 2(a) and 2(b)). This was shown using in vitro complementation assays with ceramide vesicles and purified proteins, but also in living cells visualizing S18-induced polarity protein complexes by immunocytochemistry [16, 17, 20–22]. Most excitingly, by developing a highly specific antibody against ceramide, we could show that the S18-induced protein complexes were identical to those associated with ceramide [16, 17, 23]. Therefore, our studies explained for the first time how ceramide can organize cell polarity on the molecular level.


Ceramide in stem cell differentiation and embryo development: novel functions of a topological cell-signaling lipid and the concept of ceramide compartments.

Bieberich E - J Lipids (2010)

Structure of aPKC and the “flipside” model of ceramide activity. (a) In aPKC (Figure shows PKCζ), the N-terminal (regulatory) and C-terminal (catalytic) moieties are connected by a hinge region. The N-terminus contains a pseudosubstrate (PS) motif and a PB1 domain. The PB1 domain is associated with the polarity protein Par6 that itself binds to Cdc42. The hinge region contains a C1b domain that has been suggested to be associated with ceramide and is a putative binding site for PAR-4. The C-terminal moiety contains the catalytic domain and several phosphorylation sites involved in activation of the enzyme. Most recently, we have constructed a dominant negative mutant from the C-terminus of aPKC (C20ζ-GFP) that binds to ceramide. Therefore, aPKC may contain two distinct ceramide-binding sites. In the inactive state of aPKC, the N-terminal PS motif “folds back” onto the C-terminal catalytic domain and blocks its access to protein substrates. We have proposed that binding to ceramide “opens up” aPKC and primes its activation by phosphorylation or inhibition by PAR-4 (Flipside model of ceramide activity). (b) For the activation reaction, ceramide binding to aPKC is followed by its association with Par6 and Cdc42. PIP2 or 3 may participate in aPKC activation and subcellular translocation by binding to active (GTP-associated) Cdc42 in this complex. This ceramide-aPKC polarity complex (CAP-PC) may inhibit GSK-3β and control cell polarity, process formation/migration, or ciliogenesis as described in Figure 3. In the presence of increased levels of active PAR-4, ceramide-associated aPKC binds to PAR-4 and forms a ceramide-aPKC apoptosis complex (CAP-AC). This complex inhibits aPKC and prevents activation of its downstream targets, NF-κB and Akt. We have proposed that this leads to activation of Bax/Bad and induction of apoptosis.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3066852&req=5

fig2: Structure of aPKC and the “flipside” model of ceramide activity. (a) In aPKC (Figure shows PKCζ), the N-terminal (regulatory) and C-terminal (catalytic) moieties are connected by a hinge region. The N-terminus contains a pseudosubstrate (PS) motif and a PB1 domain. The PB1 domain is associated with the polarity protein Par6 that itself binds to Cdc42. The hinge region contains a C1b domain that has been suggested to be associated with ceramide and is a putative binding site for PAR-4. The C-terminal moiety contains the catalytic domain and several phosphorylation sites involved in activation of the enzyme. Most recently, we have constructed a dominant negative mutant from the C-terminus of aPKC (C20ζ-GFP) that binds to ceramide. Therefore, aPKC may contain two distinct ceramide-binding sites. In the inactive state of aPKC, the N-terminal PS motif “folds back” onto the C-terminal catalytic domain and blocks its access to protein substrates. We have proposed that binding to ceramide “opens up” aPKC and primes its activation by phosphorylation or inhibition by PAR-4 (Flipside model of ceramide activity). (b) For the activation reaction, ceramide binding to aPKC is followed by its association with Par6 and Cdc42. PIP2 or 3 may participate in aPKC activation and subcellular translocation by binding to active (GTP-associated) Cdc42 in this complex. This ceramide-aPKC polarity complex (CAP-PC) may inhibit GSK-3β and control cell polarity, process formation/migration, or ciliogenesis as described in Figure 3. In the presence of increased levels of active PAR-4, ceramide-associated aPKC binds to PAR-4 and forms a ceramide-aPKC apoptosis complex (CAP-AC). This complex inhibits aPKC and prevents activation of its downstream targets, NF-κB and Akt. We have proposed that this leads to activation of Bax/Bad and induction of apoptosis.
Mentions: S18 is a special kind of ceramide analog designed and synthesized in our laboratory [18, 19]. By maintaining the polar (serine-derived) head group of ceramide, and at the same time, enhancing the water solubility of the lipophilic portion, we obtained a water-soluble, but still lipophilic, structural analog of ceramide (Figure 1). The extensive characterization of S18 showed that it incorporates into cell membranes and activates atypical PKC (aPKC), which was also found for ceramide [18–21]. Moreover, ceramide and S18 induce the formation of aPKC-associated complexes with polarity proteins such as Par6 and the small Rho-type GTPase Cdc42 (Figures 2(a) and 2(b)). This was shown using in vitro complementation assays with ceramide vesicles and purified proteins, but also in living cells visualizing S18-induced polarity protein complexes by immunocytochemistry [16, 17, 20–22]. Most excitingly, by developing a highly specific antibody against ceramide, we could show that the S18-induced protein complexes were identical to those associated with ceramide [16, 17, 23]. Therefore, our studies explained for the first time how ceramide can organize cell polarity on the molecular level.

Bottom Line: In the last two decades, the view on the function of ceramide as a sole metabolic precursor for other sphingolipids has completely changed.A plethora of studies has shown that ceramide is an important lipid cell-signaling factor regulating apoptosis in a variety of cell types.Recent studies suggest that ceramide is a critical cell-signaling factor for stem cell differentiation and cell polarity, two processes at the core of embryo development.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Neurobiology, Institute of Molecular Medicine and Genetics, School of Medicine, Medical College of Georgia, 1120 15th Street Room CA4012, Augusta, GA 30912, USA.

ABSTRACT
In the last two decades, the view on the function of ceramide as a sole metabolic precursor for other sphingolipids has completely changed. A plethora of studies has shown that ceramide is an important lipid cell-signaling factor regulating apoptosis in a variety of cell types. With the advent of new stem cell technologies and knockout mice for specific steps in ceramide biosynthesis, this view is about to change again. Recent studies suggest that ceramide is a critical cell-signaling factor for stem cell differentiation and cell polarity, two processes at the core of embryo development. This paper discusses studies on ceramide using in vitro differentiated stem cells, embryo cultures, and knockout mice with the goal of linking specific developmental stages to exciting and novel functions of this lipid. Particular attention is devoted to the concept of ceramide as a topological cell-signaling lipid: a lipid that forms distinct structures (membrane domains and vesicles termed "sphingosome"), which confines ceramide-induced cell signaling pathways to localized and even polarized compartments.

No MeSH data available.


Related in: MedlinePlus