Treatment of MM cells with the SphK1 inhibitor SK1-I decreased SphK1 active protein levels, as expected, and this was accompanied by dose-dependent diminished protein levels of c-Myc in MM cells (MM.1S, OPM-2 and KMS-11), regardless of their p53 status (Figure 6A). This evidence concerns the gene TP53 and Miyoshi myopathy.