Abstract 975: MicroRNA-155 In chronic lymphocytic leukemia influences B-cell receptor signaling

MicroRNAs (miRNAs) can influence the expression levels of genes that can affect the clinical outcome of patients with chronic lymphocytic leukemia (CLL). In a well-defined cohort of 86 patients, we observed heterogeneity in the relative leukemia-cell expression of miR-155. Cases that expressed high-levels of miR-155 more frequently expressed zeta-associated protein of 70 kD (ZAP-70), used unmutated Ig heavy-chain-variable-region genes (IGHV), and had shorter treatment-free survival (TFS) and overall survival (OS) than cases with low-level expression of miR-155. Recursive partitioning allowed us to define a threshold for “high-level” expression of miR-155 (in copy numbers per CLL cell) that best associates with adverse clinical outcome. We examined the potential basis for this association. One of the genes targeted by miR-155 encodes the phosphatidylinositol polyphosphate 5-phosphatase SHIP-1, which can dephosphorylate proteins that had been activated in response to B-cell receptor (BCR) ligation. We found that CLL cells with “high-level” miR-155 expressed significantly lower levels of SHIP-1 protein and were more sensitive to ligation of surface-µ than CLL cells with low-levels of miR-155. Transfecting CLL cells with miR-155 reduced their expression of SHIP-1 and enhanced the stimulatory-response to surface-µ ligation. Conversely, transfection of CLL cells with a miR-155 inhibitor had the opposite effects. The enhanced sensitivity to BCR-ligation of cells expressing “high-level” miR-155 may account for its association with adverse clinical outcome in patients with CLL. However, within any one patient we also find heterogeneity in the expression levels of miR-155. By GEO data analysis (GSE21029) we found that CLL cells in blood expressed lower levels of miR-155 than did CLL cells in lymphoid tissues, where they interact with supportive cells, such as Nurselike cells or activated T cells, which can provide survival- or growth-promoting signals via expression of BAFF/APRIL or CD40L, respectively. We found that stimulation of CLL cells in vitro via CD40 ligation or exogenous BAFF could induce higher expression of miR-155, leading to reduced leukemia-cell expression of SHIP-1 and enhanced sensitivity to surface-µ ligation. Moreover, we found that the “proliferative” subgroup of blood CD5brightCXCR4dim CLL cells, which represent CLL cells newly released from the tissue microenvironment, expressed higher level of miR-155 and lower levels of SHIP-1 protein, and were more sensitive to surface-µ ligation than the “resting” subgroup of blood CD5dimCXCR4bright CLL cells, which represent cells that may be due to enter the tissue microenvironment. As such, this study also demonstrates that miR-155 could be upregulated by signals in the CLL microenvironment, leading to lower-level expression of SHIP-1, and enhanced stimulation in response to BCR ligation. Citation Format: Liguang Chen, Bing Cui, Suping Zhang, Marek Mraz, Jessie-F. Fecteau, Jian Yu, Ling Zhang, Lei Bao, Laura Rassenti, Karen Messer, Carlo Croce, Thomas Kipps. MicroRNA-155 In chronic lymphocytic leukemia influences B-cell receptor signaling. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 975. doi:10.1158/1538-7445.AM2014-975