Altered de novo sphingolipid biosynthesis is involved in the serum deprivation-induced cell death in LLC-PK1 cells

Fumonisin B₁, a specific inhibitor of ceramide synthase, and ISP1 (Myriocin), a serine palmitoyl-transferase 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 M to 30 M 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 M 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.