ALTERED DE NOVO SPHINGOLIPID BIOSYNTHESIS IS INVOLVED IN THE SERUM DEPRIVATION-INDUCED CELL DEATH IN LLC-PK1 CELLS

Abstract

Fumonisin B₁, a specific inhibitor of ceramide synthase, and ISPI (Myriocin), a serine palmitoyltransferase inhibitor, modulate the de novo sphingolipid biosynthesis pathway. This study was conducted to determine whether serum deprivation-induced cell death is regulated by de novo sphingolipid biosynthesis in pig kidney LLC-PK1 cells. Serum withdrawal from the culture medium produced cell death in LLC-PK1 cells. Fumonisin B₁ at concentrations ranging from 5 µM to 30 µM delayed until 48 h this cell death resulting from the absence of fetal bovine serum (FBS) in cell culture. Pretreatment of cultured cells with fumonisin B₁ in the presence of serum for 24 h increased by approximately 70% this cytoprotective activity of fumonisin B₁ against serum deprivation-induced cell death. Serum deprivation increased sphingolipid biosynthesis threefold compared to 5% serum-enriched culture. Fumonisin B₁ at 5–30 µM lowered the content of total complex sphingolipids to levels of 50% and 77% of the content in serum-enriched culture, although the concentration of intracellular free sphinganine was elevated. ISP1 alone at greater than 1 nM concentration reduced total complex sphingolipid content to values in LLC-PK1 cells grown in the presence of 5% FBS. The results suggest that the de novo complex sphingolipid biosynthesis modulated by either fumonisin B₁ or ISP1 may regulate serum deprivation-induced cell death in LLC-PK1 cells.

This work was supported by a grant (R01-2002-000-00457-0) from the Basic Research Program of the Korea Science & Engineering Foundation and by Brain Korea 21 project in 2003.