Acid Ceramidase in Melanoma

Abstract

Acid ceramidase (AC) is a lysosomal cysteine amidase that controls sphingolipid signaling by lowering the levels of ceramides and concomitantly increasing those of sphingosine and its bioactive metabolite, sphingosine 1-phosphate. In the present study, we evaluated the role of AC-regulated sphingolipid signaling in melanoma. We found that AC expression is markedly elevated in normal human melanocytes and proliferative melanoma cell lines, compared with other skin cells (keratinocytes and fibroblasts) and non-melanoma cancer cells. High AC expression was also observed in biopsies from human subjects with Stage II melanoma. Immunofluorescence studies revealed that the subcellular localization of AC differs between melanocytes (where it is found in both cytosol and nucleus) and melanoma cells (where it is primarily localized to cytosol). In addition to having high AC levels, melanoma cells generate lower amounts of ceramides than normal melanocytes do. This downregulation in ceramide production appears to result from suppression of the de novo biosynthesis pathway. To test whether AC might contribute to melanoma cell proliferation, we blocked AC activity using a new potent (IC 50 ‫؍‬ 12 nM) and stable inhibitor. AC inhibition increased cellular ceramide levels, decreased sphingosine 1-phosphate levels, and acted synergistically with several, albeit not all, antitumoral agents. The results suggest that AC-controlled sphingolipid metabolism may play an important role in the control of melanoma proliferation.Ceramides are a class of bioactive lipids that regulate senescence, apoptosis, and autophagy (1). They comprise more than 200 chemically and functionally distinct molecules and are produced through either de novo biosynthesis or cleavage of preformed sphingolipid precursors in membranes (2-4). They are degraded by the action of five distinct ceramidases, which differ in sequence, structure, subcellular localization, and preferred substrates (5). Among them, acid ceramidase (AC) 2 (also known as N-acetylsphingosine amidohydrolase, ASAH1) is especially relevant due to its possible roles in cancer progression and chemoresistance (6). AC is a lysosomal cysteine amidase that catalyzes the hydrolysis of ceramide into sphingosine and fatty acid with a preference for unsaturated ceramides with 6 -16-carbon acyl chains (5). Its activation is associated with decreased cellular levels of these medium-chain ceramides, which promote senescence and apoptosis, and increased levels of sphingosine 1-phosphate (S1P), which stimulates cell proliferation and cancer cell migration (7). A bioinformatic survey of the National Cancer Institute (NCI) gene expression database conducted in 2003 identified AC as a potential candidate for the development of new biomarkers for the prognosis of melanoma (8). Supporting this possibility, subsequent studies showed that serum of melanoma patients contains AC autoantibodies (9). Moreover, experiments with melanoma cell lines in cultures have demonstrated that dacarbazine, a standard of care for the...

MITF—the first 25 years

“…Recent evidence also indicates that MITF can control the expression of the lysosomal acid ceramidase ASAH1 that controls sphingolipid metabolism (Leclerc et al 2019). Significantly ectopic expression of ASAH1 could rescue the cell cycle defects associated with MITF depletion, consistent with a role for ASAH1 in promoting melanoma proliferation (Realini et al 2016). Moreover, MITF in melanoma has recently been identified as a regulator of a subset of genes implicated in autophagy (Moller et al 2019), a lysosome-dependent process that degrades and recycles unwanted organelles and may represent a key survival strategy of cells under nutrient restriction.…”

The emergence of acid ceramidase as a therapeutic target for acute myeloid leukemia

“…ARN14899 decreased AC activity with an IC 50 of 12nM and induced ceramide accumulation. Alone, the compound was only mildly toxic at micromolar concentrations, but viability of proliferative melanoma cells was drastically reduced when combined with chemotherapeutics 45 . Benzoxazolone carboxamide prototypes have also been studied as potent acid ceramidase inhibitors 74, 75 .…”

Role of Ceramidases in Sphingolipid Metabolism and Human Diseases

“…The altered function of mutated ASAH1 has been recognized in spinal muscular atrophy with progressive myoclonic epilepsy [25] and Farber's lipogranulomatosis [11]. In the case of metabolic disorders, there is either an alteration in acid ceramidase activity or a change in the expression level of ASAH1 in Alzheimer's disease [26], cancer [27][28][29], and type 2 diabetes [30].…”

“…∼4.0-4.5 Heart, kidneys, lungs, placenta, etc. [48] Lysosomes [48] Farber's disease, Alzheimer's disease, cancer, diabetes, and spinal muscular atrophy [11,[25][26][27][28]30,49] Neutral ceramidase ASAH2, located at q11.23 of chromosome 10 ∼7.0-7.4 Small intestine [33] Mitochondria (HEK293T overexpressing cells) [31] Alzheimer's disease [50], various metabolic diseases [51][52][53] Plasma membrane (HEK293T overexpressing cells) [32,34] Mitochondria and Golgi (HCT116 overexpressing cells) [54] Alkaline ceramidase ACER1, located at p13.3 of chromosome 19…”