Sphingolipids in colon cancer

Colorectal cancer is one of the major causes of death in the western world. Despite increasing knowledge of the molecular signaling pathways implicated in colon cancer, therapeutic outcomes are still only moderately successful. Sphingolipids, a family of N-acyl linked lipids, have not only structural functions but are also implicated in important biological functions. Ceramide, sphingosine and sphingosine-1-phosphate are the most important bioactive lipids, and they regulate several key cellular functions. Accumulating evidence suggests that many cancers present alterations in sphingolipids and their metabolizing enzymes. The aim of this review is to discuss the emerging roles of sphingolipids, both endogenous and dietary, in colon cancer and the interaction of sphingolipids with WNT/β-catenin pathway, one of the most important signaling cascades that regulate development and homeostasis in intestine. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.     

Long-chain glucosylceramides crosstalk with LYN mediates endometrial cell migration

Endometriosis is a disease characterized by regurgitated lesions which are invasive and migratory, embedding at ectopic, extra-uterine locations. Extracellular glucosylceramides (GlcCers), bioactive sphingolipids potentiating signals for cell migration, are found in elevated levels in endometriosis; however underlying mechanisms that result in cellular migration are poorly defined. Here, we demonstrated that internalized GlcCer induced migratory activity in immortalized human endometrial stromal cells (HESCs), with highest potency observed in long-chain GlcCer. Long-chain ceramide (Cer) similarly induced cellular migration and mass spectrometry results revealed that the migratory behavior was contributed through glycosylation of ceramides. Cells treated with GlcCer synthase inhibitor, or RNAi-mediated knockdown of glucosylceramide synthase (GCS), the enzyme catalyzing GlcCer production attenuated cell motility. Mechanistic studies showed that GlcCer acts through stromal cell-derived factor-1 alpha and its receptor, CXC chemokine receptor 4 (SDF-1α-CXCR4) signaling axis and is dependent on phosphorylation of LYN kinase at Tyr396, and dephosphorylation of Tyr507. Migration was prominently attenuated in cells exposed to CXCR4 antagonist, AMD3100, yet can be rescued with diprotin A, which prevents the degradation of SDF-1α. Furthermore, blocking of LYN kinase activity in the presence of SDF-1α and GlcCer reduced HESC migration, suggesting that LYN acts downstream of GlcCer-SDF-1α-CXCR4 axis as part of its intracellular signal transduction. Our results reveal a novel role of long-chain GlcCer and the dialog between GlcCer, LYN^pTyr396 and SDF-1α-CXCR4 in inducing HESC migration. This finding may improve our understanding how endometriotic lesions invade to their ectopic sites, and the possibility of using GlcCer to modulate the SDF-1α-CXCR4-LYN^pTyr396 axis in endometriosis.     

Sphingolipids as modulators of cancer cell death: Potential therapeutic targets

Through modifications in the fine membrane structure, cell-cell or cell-matrix interactions, and/or modulation of intracellular signaling pathways, sphingolipids can affect the tumorigenic potential of numerous cell types. Whereas ceramide and its metabolites have been described as regulators of cell growth and apoptosis, these lipids as well as other sphingolipid molecules can modulate the ability of malignant cells to grow and resist anticancer treatments, and their susceptibility to non-apoptotic cell deaths. This review summarizes our current knowledge on the properties of sphingolipids in the regulation of cancer cell death and tumor development. It also provides an update on the potential perspectives of manipulating sphingolipid metabolism and using sphingolipid analogues in anticancer therapy.     

Direct visualization of saposin remodelling of lipid bilayers

Saposins A, B, C and D are soluble, non-enzymatic proteins that interact with lysosomal membranes to activate the breakdown and transfer of glycosphingolipids. The mechanisms of hydrolase activation and lipid transfer by saposins remain unknown. We have used in situ atomic force microscopy (AFM) with simultaneous confocal fluorescence microscopy to investigate the interactions of saposins with lipid membranes. AFM images of the effect of saposins A, B and C on supported lipid bilayers showed a time and concentration-dependent nucleated spread of membrane transformation. Saposin B produced deep gaps that ultimately filled with granular material, while saposins A and C lead to localized areas of membrane that were reduced in height by approximately 1.5 nm. Fluorescence-labeled saposin C co-localized with the transformed areas of the bilayer, indicating stable binding to the membrane. Fluorescence resonance energy transfer confirmed a direct interaction between saposin C and lipid. Under certain conditions of membrane lipid composition and saposin concentration, extensive bilayer lipid removal was observed. We propose a multi-step mechanism that integrates the structural features and amphipathic properties of the saposin proteins.     

Cell cycle arrest in Batten disease lymphoblast cells

Batten disease is an inherited neurodegenerative disorder caused by a CLN3 gene mutation. Batten disease is characterized by blindness, seizures, cognitive decline, and early death. Although apoptotic cell death is one of the pathological hallmarks of Batten disease, little is known about the regulatory mechanism of apoptosis in this disease. Since the CLN3 gene is suggested to be involved in the cell cycle in a yeast model, we investigated the cell cycle profile and its regulatory factors in lymphoblast cells from Batten disease patients. We found G1/G0 cell cycle arrest in Batten disease cells, with overexpression of p21, sphingosine, glucosylceramide, and sulfatide as possible cell cycle regulators.     

Epidermal sphingolipids: metabolism, function, and roles in skin disorders

Mammalian epidermis produces and delivers large quantities of glucosylceramide and sphingomyelin precursors to stratum corneum extracellular domains, where they are hydrolyzed to corresponding ceramide species. This cycle of lipid precursor formation and subsequent hydrolysis represents a mechanism that protects the epidermis against potentially harmful effects of ceramide accumulation within nucleated cell layers. Prominent skin disorders, such as psoriasis and atopic dermatitis, have diminished epidermal ceramide levels, reflecting altered sphingolipid metabolism, that may contribute to disease severity/progression. Enzymatic processes in the hydrolysis of glucosylceramide and sphingomyelin, and the roles of sphingolipids in skin diseases, are the focus of this review.