SPHK1 and mesothelioma: Down-regulation of SphK1 with specific siRNA for 48 h (>80% loss in specific protein expression, data not shown) attenuated mRNA levels of CBP and p300/CBP-associated factor (PCAF) in mesothelioma cell line H2691, but not the control Met5A cells (Fig. 8A and 8B).