SK2 was overexpressed in myeloma cells. (A) SK1 and SK2 gene expression in GSE6477 Affymetrix microarray dataset. Publicly available Affymetrix microarray data set GSE6477 was downloaded and the RMA normalized gene expression data were generated. The SK1 and SK2 expression levels between plasma cells from normal subjects (blue bar; n = 15) and purified CD138⁺ cells from newly diagnosed MM (red bar; n = 73) were compared. (B) SK1 and SK2 expression in myeloma cell lines and B-cell lines. RNA was extracted from 2 B-cell lines (EBV-immortalized B cells (IBC) and American Type Culture Collection (ATCC) CCL-156 B-lymphocytes) and 7 MM cell lines (NCI-H929, OPM1, U266, RPMI-8226, RPMI-8226-Dox40, MM.1R, and MM.1S) and RT-PCR was performed for SK1 and SK2. Relative SK1 and SK2 mRNA expression with respect to β-actin was shown (mean ± standard error of the mean of 3 separate sets of experiments). (C) SK2 expression in primary human BM CD138⁺ cells. Primary human CD138⁺ cells were isolated using CD138 enrichment kit from the BM aspirates of normal subjects (n = 5), monoclonal gammopathy of undetermined significance patients (n = 6), and myeloma patients (n = 34). SK2 gene expression was normalized against β-actin control. (Each dot represented 1 individual patient and the two solid circles represented amyloidosis patients). (D) Sphingosine level in myeloma cell lines and B-cell lines. Sphingosine was measured by high performance liquid chromatography (HPLC) in freshly prepared Epstein-Barr virus (EBV)-immortalized B cells, ATCC B-lymphocytes, and 6 MM cell lines (NCI-H929, OPM1, U266, RPMI-8226, RPMI-8226-Dox40, and MM.1S). Data represented the sphingosine concentration (pmol/1 × 10⁶ cells) (mean ± standard error of the mean of 1 of 4 separate sets of experiments) (*P < .05; **P < .01).