High Membrane Cholesterol in CLL B-Cells and Differential Expression of Cholesterol Synthesis Genes in IG GENE-Unmutated vs Mutated Cells

Abstract

Objectives: Chronic lymphocytic leukaemia (CLL) is associated with abnormalities of the B-Cell Receptor (BCR) signalling, including low responsiveness to antigenic stimulation and constitutive phosphorylation of several components of the signalling pathway. In B-cells, BCR-mediated signalling is regulated in part by the amount of membrane cholesterol. It was observed that Statins, pharmacological inhibitors of cholesterol synthesis, induce apoptosis of CLL cells in vitro and in vivo. Having previously reported that ectopic expression of CD5 in a B-cell line stimulated the transcription of genes involved in the synthesis of cholesterol, we investigated the expression and synthesis of cholesterol in CLL B-cells. Study Design & Methodology: Plasma membrane cholesterol in CLL cells was evaluated by staining with Filipin and Flow cytometry in 26 patients. CLL cells were cultured with Lovastatin and subG1 cells and Gumprecht’s shadows counted thereafter; surface expression of IgM, CD19 and CD5 was analysed. The expression of cholesterol synthesis genes was investigated in transcriptomic data from the MILE project (150 CLL and 110 controls). Results: We confirmed that leukemic B-cells contained more cholesterol in their plasma membranes than their normal counterparts. An enhanced expression of genes involved in the synthesis of cholesterol in CLL as compared to healthy controls was observed. Interestingly, among the 150 CLL patients analyzed, four cholesterol synthesis genes were activated in 65 “Ig-mutated” (M) in comparison to 69 “Ig-unmutated” (UM) CLLs. Leukemic cells cultured with Lovastatin exhibited a dose-response apoptosis, however surface IgM expression was unaffected and CD19 and CD5 were downregulated at highest concentrations only. Conclusions: High membrane cholesterol in CLL cells may explain their sensitivity to Statins, with a potential difference between UM- and M-CLL.