Altered sphingolipid metabolism in multidrug‐resistant ovarian cancer cells is due to uncoupling of glycolipid biosynthesis in the Golgi apparatus

Abstract

Multidrug-resistant tumor cells display enhanced levels of glucosylceramide. In this study, we investigated how this relates to the overall sphingolipid composition of multidrug-resistant ovarian carcinoma cells and which mechanisms are responsible for adapted sphingolipid metabolism. We found in multidrug-resistant cells substantially lower levels of lactosylceramide and gangliosides in sharp contrast to glucosylceramide, galactosylceramide, and sphingomyelin levels. This indicates a block in the glycolipid biosynthetic pathway at the level of lactosylceramide formation, with concomitant accumulation of glucosylceramide. A series of observations exclude regulation at the enzyme level as the underlying mechanism. First, reduced lactosylceramide formation occurred only in intact resistant cells whereas cell-free activity of lactosylceramide synthase was higher compared with the parental cells. Second, the level of lactosylceramide synthase gene expression was equal in both phenotypes. Third, glucosylceramide synthase (mRNA and protein) expression and activity were equal or lower in resistant cells. Based on the kinetics of sphingolipid metabolism, the observation that brefeldin A does not restore lactosylceramide synthesis, and altered localization of lactosylceramide synthase fused to green fluorescent protein, we conclude that lactosylceramide biosynthesis is highly uncoupled from glucosylceramide biosynthesis in the Golgi apparatus of resistant cells.

Altered Sphingolipid Metabolism inN-(4-Hydroxyphenyl)- retinamide-resistant A2780 Human Ovarian Carcinoma Cells

“…In the well studied case of multidrug resistance (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)14), MDR cells are able to escape the drug-induced apoptotic death elicited in their sensitive counterparts by a rise in the cellular ceramide levels through two distinctive features. MDR cells express high levels of efflux pump proteins belonging to the ATP-binding cassette superfamily of membrane transport proteins, such as MDR1 and MRP.…”

“…Interestingly, in tumor cell lines, resistance to chemotherapeutic treatments is often associated with an increased ability of the cell to glycosylate ceramide, as a consequence of a higher activity of glucosylceramide synthase (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). High levels of GlcCer 1 (6 -9, 11, 12) and of glucosylceramide synthase activity (5,8,9) and/or expression (8,9,11,12) were detected in a number of drug-resistant cancer cell lines and in specimens from cancer patients not responding to chemotherapy treatment (13).…”

“…High levels of GlcCer 1 (6 -9, 11, 12) and of glucosylceramide synthase activity (5,8,9) and/or expression (8,9,11,12) were detected in a number of drug-resistant cancer cell lines and in specimens from cancer patients not responding to chemotherapy treatment (13). GlcCer accumulation results in the ability of drugresistant cells to scavenge ceramide, thus preventing ceramideinduced apoptotic death.…”

“…On the other hand, it has been shown (12,15) that GlcCer accumulation is not the only consequence of an altered sphingolipid metabolism in MDR cancer cells. In MDR human ovarian carcinoma cells, SM and galactosylceramide levels are also higher respect to parental sensitive cells, whereas LacCer and all of the more complex GSLs are present in lower amounts.…”

Strategies for overcoming p-glycoprotein-mediated drug resistance in acute myeloblastic leukaemia

“…It is thought to affect apoptosis through multiple effects on the ceramide pathway including modulation of sphingomyelin transbilayer movement, glucosylceramide transport and lactosylceramide formation. [11][12][13] Pgp may also play an active role in stabilising cholesterol-rich rafts and caveolae by relocating cholesterol from the cytosolic to exoplasmic leaflet of the plasma membrane. 14 Ceramide has been demonstrated to have a key role in activating cell death initiated by cytotoxic drugs (see Figure 1).…”