Impairment of ribosomes and DNA biosynthesis confers resistance to Inhibition of sphingolipid biosynthesis.

Sphingolipids are essential components of eukaryotic membranes and play central roles in cellular growth and stress responses. In the budding yeast Saccharomyces cerevisiae, Lcb1 and Lcb2 constitute the serine palmitoyltransferase complex, which catalyzes the initial step of sphingolipid biosynthesis. Repression of LCB1 expression leads to inhibition of sphingolipid biosynthesis, resulting in severe growth defects. Here, we aimed to identify novel genes functionally associated with sphingolipid metabolism by screening for suppressor mutations that confer resistance to sphingolipid biosynthesis inhibition. To conditionally suppress sphingolipid biosynthesis, we employed a tetracycline-repressible promoter to control LCB1 expression. This screen revealed that deletion of SAC7, YTA7, RNR1, RPL23B, or RPL35A confers resistance to LCB1 repression. The suppressive effect of YTA7, RNR1, RPL23B, and RPL35A deletions was also observed under conditions in which growth inhibition was induced by repression of AUR1, a gene involved in the conversion of ceramides to complex sphingolipids. These genes encode proteins related to ribosomal subunits or DNA biosynthesis. Furthermore, sublethal concentrations of cycloheximide (a translation inhibitor), diazaborine (a ribosome maturation inhibitor), hydroxyurea (a DNA biosynthesis inhibitor), and zeocin (a DNA double-strand break inducer) alleviated growth defects caused by LCB1 repression. Diazaborine or hydroxyurea partly suppressed the decrease in complex sphingolipids induced by Lcb1 repression. Additionally, these treatments suppressed the reduction in Lcb1 and Aur1 protein expression levels. These findings reveal a previously unappreciated link between ribosome function, DNA biosynthesis, and sphingolipid metabolism and provide insight into how cells adapt to metabolic stress.