Taxoids are anti-cancer drugs frequently used to treat solid tumors, but they are sometimes ineffective and tumors may become resistant to their action. Here, we examined the involvement of sphingolipid metabolic enzymes in paclitaxel (PTX) resistance using a human prostate cancer cell line, PO, and its PTX-resistant subline, PO-PR. PTX (20 nM) suppressed cell proliferation and increased various ceramide species in PO, but not PO-PR, cells. PO-PR contained higher S1P levels than did PO, regardless of FIX treatment. Western blotting revealed that PO-PR cells expressed higher levels of sphingosine kinase 1 (SPHK1) and glucosylceramide synthase (GCS) but lower levels of acid sphingomyelinase (ASMase) and neutral sphingomyelinase 2 than did PO cells. Inhibition of SPHK1 using siRNA or a pharmacological inhibitor decreased SIP levels in PO-PR cells and inhibited proliferation in the presence or absence of PTX, suggesting that SPHK1 is at least partially responsible for PTX resistance. Similarly, GCS inhibitors (PDMP and PPMP) increased cellular ceramides and suppressed the proliferation of PO-PR. However, inhibition of proteasome function or histone deacetylase activity increased SMase and ceramide levels and suppressed PO-PR proliferation. These results suggest that modulation of metabolic enzyme expression and alteration of the sphingolipid rheostat protects cancer cells against PTX. (C) 2017 Elsevier Inc. All rights reserved.