Overexpression of Sphingosine-1-Phosphate Lyase or Inhibition of Sphingosine Kinase in Dictyostelium discoideum Results in a Selective Increase in Sensitivity to Platinum-Based Chemotherapy Drugs

Abstract

The efficacy of the chemotherapy drug cisplatin is often limited due to resistance of the tumors to the drug, and increasing the potency of cisplatin without increasing its concentration could prove beneficial. A previously characterized Dictyostelium discoideum mutant with increased resistance to cisplatin was defective in the gene encoding sphingosine-1-phosphate (S-1-P) lyase, which catalyzes the breakdown of S-1-P, an important regulatory molecule in cell function and development and in the regulation of cell fate. We hypothesized that the increased resistance to cisplatin was due to an elevation of S-1-P and predicted that lowering levels of S-1-P should increase sensitivity to the drug. We generated three strains that stably overexpress different levels of the S-1-P lyase. The overexpressor strains have reduced growth rate and, confirming the hypothesis, showed an expression-dependent increase in sensitivity to cisplatin. Consistently, treating the cells with D-erythro-N,N,-dimethylsphingosine, a known inhibitor of sphingosine kinase, increased the sensitivity of mutant and parent cells to cisplatin, while addition of exogenous S-1-P or 8-Br-cyclic AMP made the cells more resistant to cisplatin. The increased sensitivity of the overexpressors to cisplatin was also observed with the cisplatin analog carboplatin. In contrast, the response to doxorubicin, 5-flurouracil, or etoposide was unaffected, indicating that the involvement of the sphingolipid metabolic pathway in modulating the response to cisplatin is not part of a global genotoxic stress response. The augmented sensitivity to cisplatin appears to be the result of an intracellular signaling function of S-1-P, because D. discoideum does not appear to have endothelial differentiation growth (EDG/S1P) receptors. Overall, the results show that modulation of the sphingolipid pathway at multiple points can result in increased sensitivity to cisplatin and has the potential for increasing the clinical usefulness of this important drug.

Global transcriptional responses to cisplatin in Dictyostelium discoideum identify potential drug targets

“…This suggests that transcriptional regulation of nucleotide metabolism and protein synthesis genes is part of the general drug response, whereas regulation of cell proliferation is unique to the mutants and may be part of the response that allows the mutants to resist cisplatin treatment. The latter notion is consistent with the known effects of sphingosine metabolism on cell proliferation (13). Tables 7 and 8).…”

“…2). The survival rates were similar to those reported previously (9,13,14): no significant difference between the survival rates of the untreated strains (0 M) (Fig. 2 A), a small but significant increase in the sglA Ϫ cell survival, and a large and significant increase in the sgkA OE cell survival compared with the parental cells after cisplatin treatment (300 M) (Fig.…”

“…cells. We have previously shown that cisplatin sensitivity in D. discoideum and in human cells is reduced by overexpression of the sphingosine kinase gene sgkA (sgkA OE ) or by deletion of the S-1-P lyase gene sglA (sglA Ϫ ) (13,14,26). Current models propose that sphingolipid metabolism modulates the cisplatin response through second-messenger signaling (2).…”

“…Cells overexpressing sphingosine kinase or null for S-1-P lyase are less sensitive to cisplatin, and cells null for sphingosine kinase or overexpressing S-1-P lyase are more sensitive to cisplatin. The change in sensitivity is specific to cisplatin and carboplatin (9,13,14) and is associated with the activation of MAP kinases and signal transduction pathways in human cells (11,12).…”

Sphingosine-1-Phosphate Lyase Regulates Sensitivity of Human Cells to Select Chemotherapy Drugs in a p38-Dependent Manner

“…Subsequent genetic studies in D. discoideum have firmly established the centrality of this pathway in controlling sensitivity to cisplatin in this organism (7,8). As predicted, overexpression of the S-1-P lyase had the opposite effect of the null mutation and resulted in increased sensitivity to cisplatin.…”