RESUMO
The current study characterizes the lipogenic enzyme fatty acid synthase (FAS; EC 2.3.1.85) in pediatric tumor cell lines of neural or neural crest origin [medulloblastoma (Daoy), malignant rhabdoid tumor of kidney (SM II), retinoblastoma (Y79), and neuroblastoma (SK-N-SH)]. Constitutive FAS content and activity in these lines were compared to human fibroblast cell line Hs27. Hs27 exhibits low levels of FAS and recapitulates enzyme status in normal human tissues under most physiological conditions. Western analysis detected significantly larger amounts of FAS protein in Y79 and SK-N-SH than Daoy, SM II and Hs27. Incorporation of radiolabeled malonyl-CoA into total cellular lipid revealed that enzyme activity correlated with amount. Increased FAS content and activity in Y79 and SK-N-SH relative to the other cell lines and Hs27, in particular, implied enzyme activation in retinoblastoma and neuroblastoma lineages. The enzyme also showed evidence of hormonal regulation, as dexamethasone induced FAS protein in Daoy and SK-N-SH. However, hormonal induction of FAS protein levels did not correlate with activity levels, which led us to speculate phosphorylation as a means of regulating the enzyme's activity. Finally, the FAS inhibitor cerulenin was investigated for its ability to suppress tumor cell growth. After four days of propagation, short-term treatment of cell lines with drug produced mean IC50s less than 10.5 micrograms/ml (i.e., 5.6 +/- 1.9 for SM II; 9.3 +/- 1.5 for Daoy; 10.2 +/- 0.2 for SK-N-SH; and 10.4 +/- 2.6 for Y79). Annexin V assays revealed that cerulenin initiated apoptosis. The antineoplastic properties of cerulenin documented here are consistent with prior studies showing its cytotoxic effects upon other types of cancer cells and illustrate the potential utility of FAS inhibition as a novel chemotherapeutic approach.
