Differential regulation of sphingomyelin synthesis and catabolism in oligodendrocytes and neurons.

Neurons (both primary cultures of 3-day rat hippocampal neurons and embryonic chick neurons) rapidly converted exogenous NBD-sphingomyelin (SM) to NBD-Cer but only slowly converted NBD-Cer to NBD-SM. This was confirmed by demonstrating low in vitro sphingomyelin synthase (SMS) and high sphingomyelinase (SMase) activity in neurons. Similar results were observed in a human neuroblastoma cell line (LA-N-5).

Anti-tumor promoting effects of palmitoyl: protein thioesterase inhibitors against a human neurotumor cell line.

Inhibiting the depalmitoylation of proteins disrupts cell survival signaling in tumor cells and leads to increased cell death. We chemically synthesized a non-hydrolyzable analog of the palmitoyl-cysteine thioester linkage (AcG-alpha-ketoamido-palmitoyl diamino propionate-VKIKK) (DAPKA) and showed that it inhibits palmitoyl:protein thioesterase (PPT1) in an in vitro assay using a specific fluorescent-based (4-methylumbelliferyl-beta-gluco-6-thiopalmitate) assay. We then showed that it killed cultured tumor cells and enhanced the killing of neurotumor cells by chemotherapeutic drugs such as etoposide and adriamycin.