Gliomas are the largest category of
primary malignant brain tumors in adults, and
glioblastomas account for nearly half of
malignant gliomas.
Glioblastomas are notoriously aggressive and
drug-resistant, with a very poor 5 year survival rate of about 5%. New approaches to treatment are thus urgently needed. We previously identified an
enzyme of
fatty acid metabolism,
very long-chain acyl-CoA synthetase 3 (ACSVL3), as a potential therapeutic target in
glioblastoma. Using the
glioblastoma cell line U87MG, we created a cell line with genomic deletion of ACSVL3 (U87-KO) and investigated potential mechanisms to explain how this
enzyme supports the malignant properties of
glioblastoma cells. Compared to U87MG cells, U87-KO cells grew slower and assumed a more normal morphology. They produced fewer, and far smaller, subcutaneous xenografts in nude mice.
Acyl-CoA synthetases, including ACSVL3, convert
fatty acids to their
acyl-CoA derivatives, allowing participation in diverse downstream
lipid pathways. We examined the effect of ACSVL3 depletion on several such pathways.
Fatty acid degradation for energy production was not affected in U87-KO cells.
Fatty acid synthesis, and incorporation of de novo synthesized
fatty acids into membrane
phospholipids needed for rapid
tumor cell growth, was not significantly affected by lack of ACSVL3. In contrast, U87-KO cells exhibited evidence of altered
sphingolipid metabolism. Levels of
ceramides containing 18-22
carbon fatty acids were significantly lower in U87-KO cells. This paralleled the
fatty acid substrate specificity profile of ACSVL3. The rate of incorporation of
stearate, an 18-carbon
saturated fatty acid, into
ceramides was reduced in U87-KO cells, and proteomics revealed lower abundance of
ceramide synthesis pathway
enzymes.
Sphingolipids, including
gangliosides, are functional constituents of
lipid rafts, membrane microdomains thought to be organizing centers for receptor-mediated signaling. Both raft morphology and
ganglioside composition were altered by deficiency of ACSVL3. Finally, levels of
sphingosine-1-phosphate, a
sphingolipid signaling molecule, were reduced in U87-KO cells. We conclude that ACSVL3 supports the malignant behavior of U87MG cells, at least in part, by altering cellular
sphingolipid metabolism.