It is known for decades that the incidence of chronic lymphocytic leukemia (CLL) is significantly lower in Asia than in the Western countries, but the reason responsible for this difference still remains as a major knowledge gap. Using GeneChip® miRNA Array to analyze the global microRNA expression in B lymphocytes from Asian and Western CLL patients and healthy individuals, we have identified microRNAs with CLL-promoting or suppressive functions that are differentially expressed in Asian and Western individuals. In particular, miR-4485 is upregulated in CLL patients of both ethnic groups, and its expression is significantly lower in Asian healthy individuals. Genetic silencing of miR-4485 in CLL cells suppresses leukemia cell growth, whereas ectopic expression of miR-4485 promotes cell proliferation. Mechanistically, miR-4485 exerts its CLL-promoting activity by inhibiting the expression of TGR5 (G-protein-coupled bile acid receptor, GPBAR1) and activating the ERK1/2 (extracellular signal-regulated protein kinases 1 and 2) pathway. In contrast, miR-138, miR-181a, miR-181c, miR-181d, and miR-363 with tumor-suppressive function are highly expressed in Asian healthy individuals. Our study suggests that differential expression of several important microRNAs with pro- or anti-CLL functions in Asian and Western B lymphocytes likely contributes to the difference in CLL incidence between the two ethnic groups, and that miR-4485 and its downstream molecule TGR5 could be potential therapeutic targets.
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