Search

Structural diversity of complex sphingolipids is important for maintenance of various cellular functions; however, the overall picture of the significance of this structural diversity remains largely unknown. To investigate the physiological importance of the structural diversity of complex sphingolipids, we here constructed a complex sphingolipid structural diversity disruption library in budding yeast, which comprises 11 mutants including with combinations of deletions of sphingolipid-metabolizing enzyme genes. The sensitivity of the mutants to various environmental stresses revealed that the more the structural variation of complex sphingolipids is limited, the more stress sensitivity tends to increase. Moreover, it was found that in mutant cells with only one subtype of complex sphingolipid, Slt2 MAP kinase and Msn2/4 transcriptional factors are essential for maintenance of a normal growth and compensation for reduced tolerance of multiple stresses caused by loss of complex sphingolipid diversity. Slt2 and Msn2/4 are involved in compensation for impaired integrity of cell walls and plasma membranes caused by loss of complex sphingolipid diversity, respectively. From these findings, it was suggested that loss of structural diversity of complex sphingolipids affects the environment of the cell surface, including both plasma membranes and cell walls, which could cause multiple environmental stress hypersensitivity.

Previously, we found that yeast exhibits a strong growth defect with the combination of a lack of gene involved in structural modification of sphingolipids and repression of the phosphatidylserine synthase gene. Here we found that the double gene mutation causes reactive oxygen species-mediated cell growth defect, which is suppressed by deletion of LEM3 encoding the subunit of phospholipid flippase.

Sphingoid long-chain bases are essential intermediates of ceramides and complex sphingolipids, and function in the regulation of various signal transduction systems. Previously, we found that, in budding yeast, intracellularly accumulated dihydrosphingosine (DHS) causes mitochondrial reactive-oxygen species (ROS)-mediated cytotoxicity, which is much stronger than phytosphingosine. In this study, we screened for suppressor mutations that confer resistance to DHS, and identified RTG2 , which encodes upregulation of the mitochondrial retrograde signaling pathway (RTG pathway). Deletion of RTG3 encoding transcriptional factor for the RTG pathway suppressed the cytotoxicity of DHS, whereas deletion of MKS1 or point mutation of LST8 , both of which cause increased activity of the RTG pathway, enhanced the cytotoxicity. Moreover, the deletion of RTG3 also suppressed the DHS-induced increases in ROS levels. Finally, it was found that the RTG pathway is activated on DHS treatment. These results suggested that the cytotoxicity of DHS is partially mediated through activation of the RTG pathway. [Display omitted] • Three yeast mutants exhibiting resistance to dihydrosphingosine (DHS) were isolated. • Activation of the RTG pathway causes enhancement of the cytotoxic activity of DHS. • Loss of the RTG pathway suppresses the DHS cytotoxicity. • DHS causes activation of the RTG pathway. [ABSTRACT FROM AUTHOR]