miR-29modulates CD40 signaling in chronic lymphocytic leukemia by targeting TRAF4: an axis affected by BCR inhibitors

Abstract

B cell receptor (BCR) signaling and T cell interactions play a pivotal role in chronic lymphocytic leukemia (CLL) pathogenesis and disease aggressiveness. CLL cells can utilize microRNAs (miRNAs) and their targets to modulate microenvironmental interactions in the lymph node niches. To identify miRNA expression changes in the CLL microenvironment, we performed complex profiling of short non-coding RNAs in this context by comparing CXCR4/CD5 intraclonal cell subpopulations (CXCR4dimCD5bright vs. CXCR4brightCD5dim cells). This identified dozens of differentially expressed miRNAs including several that have previously been shown to modulate BCR signaling (miR-155, miR-150, and miR-22), but also other candidates for a role in microenvironmental interactions. Notably, all three miR-29 family members (miR-29a, miR-29b, miR-29c) were consistently down-modulated in the immune niches, and lower miR-29(a/b/c) levels associated with an increased relative responsiveness of CLL cells to BCR ligation, and significantly shorter overall survival of CLL patients. We identified Tumor-Necrosis Factor Receptor-Associated Factor 4 (TRAF4) as a novel direct target of miR-29s and revealed that higher TRAF4 levels increase CLL responsiveness to CD40 activation and downstream NFkB signaling. In CLL, BCR-represses miR-29 expression via MYC, allowing for concurrent TRAF4 upregulation and stronger CD40-NFkB signaling. This regulatory loop is disrupted by "BCR inhibitors" (BTK inhibitor ibrutinib or PI3K inhibitor idelalisib). In summary, we showed for the first time that a miRNA-dependent mechanism acts to activate CD40 signaling/T-cell interactions in a CLL microenvironment and described a novel miR-29-TRAF4-CD40 signaling axis modulated by the BCR activity.

New Insights into the Role of miR-29a in Hepatocellular Carcinoma: Implications in Mechanisms and Theragnostics

“…miR-29a has been shown to play a role in mediating immune signaling in the microenvironment of hematologic malignancy [81]. Although miR-29a has not been scrutinized intensively with respect to the immunity of HCC, a few studies have started to reveal its emerging role in this context.…”

IL4-STAT6 signaling induces CD20 in chronic lymphocytic leukemia and this axis is repressed by PI3Kδ inhibitor idelalisib

“…The CXCR4 dim CD5 bright cells are regarded as an intraclonal CLL cell subpopulation that has recently exited immune niches versus resting CXCR4 bright CD5 dim cells. 3,7 However, we could not reliably detect phosphorylated STAT6 in CLL cells by a less sensitive technic of immunoblotting suggesting that its levels were very low in peripheral blood in general.…”

“…This is underscored by the observation that in chronic lymphocytic leukemia (CLL) the combination of ibrutinib with rituximab does not provide a clinical benefit in comparison to ibrutinib alone 2 likely because ibrutinib down-modulates CD20 levels. 1, [3][4][5] PI3Kδ inhibitor idelalisib has been approved in combination with rituximab or ofatumumab; 6 however, it remains unclear if idelalisib affects CD20 levels or function(s). Here we show for the first time that single-agent idelalisib therapy in CLL leads to CD20 down-modulation in vivo by interfering with a previously unknown mechanism of CD20 transcriptional regulation via IL4-STAT6 axis.…”

“…We have recently shown a concurrent upregulation of CD20 and cell-surface IgM in CLL cells from immune niches and demonstrated that this functionally serves to increase BCR signaling propensity. 3,7 The SDF1 (CXCL12) chemokine induces ~30-50% upregulation of CD20, 3 however, this cannot fully explain the ~2-fold higher CD20 levels in CLL cells from immune niches. 3,7 Here we hypothesize that the same factor inducing cellsurface IgM in the CLL microenvironment, namely IL4 produced by T cells, 8 might also be inducing CD20.…”

“…3,7 The SDF1 (CXCL12) chemokine induces ~30-50% upregulation of CD20, 3 however, this cannot fully explain the ~2-fold higher CD20 levels in CLL cells from immune niches. 3,7 Here we hypothesize that the same factor inducing cellsurface IgM in the CLL microenvironment, namely IL4 produced by T cells, 8 might also be inducing CD20. Indeed, stimulating primary CLL cells with IL4 led to a significant upregulation of CD20 (mean fold-change 1.6-3.1 [24-72 hrs], n=25; Figure 1A-C) and IgM on the cell-surface (Figure S1A).…”