SPHK1 and Miyoshi myopathy: To determine the potential of GFI1-dependent modulation of sphingolipid metabolism to promote survival of MM cells, we evaluated the transcriptional expression of genes coding for the main enzymes that control intracellular S1P levels, SphK1 and SGPP1 (see schematic Figure S1), in MM cell lines with altered GFI1 expression.