IL-21 and CD40L signals from autologous T cells can induce antigen-independent proliferation of CLL cells

Key Points• Differentiation of CLL cells in response to IL-21 and cytosine guanine dinucleotide-enriched oligo-deoxynucleotides (CpG-ODN) is variable and linked to PRDM1 induction.• The failure of CLL cells to express or induce PRDM1 correlates with anergy.Despite antigen engagement and intact B-cell-receptor (BCR) signaling, chronic lymphocytic leukemia (CLL) cells fail to undergo terminal differentiation. We hypothesized that such failure may be due to anergy, as CLL cells exhibit variable levels of nonresponsiveness to surface IgM stimulation that is reversible in vitro. Moreover, anergy is associated with reduced differentiation capacity in normal B cells. We investigated responses of CLL cells to two potent differentiation-promoting agents, IL-21 and cytosine guanine dinucleotide-enriched oligo-deoxynucleotides. The induction of PR domaincontaining protein 1 (PRDM1; also known as Blimp-1), a critical regulator of plasmacytic differentiation, by these agents was closely correlated but varied between individual cases, despite functionally intact IL-21 receptor-and Toll-like receptor 9-mediated signal transducer and activator of transcription 3, and nuclear factor-kB pathways. PRDM1 induction was inversely correlated with the extent of anergy as measured by the ability to mobilize intracellular Ca 21 following BCR crosslinking. PRDM1 responsiveness was associated with other markers of differentiation and proliferation but not with differences in apoptosis. The ability to induce PRDM1 did correlate with differential transcriptional and epigenetic regulation of the PRDM1 gene. These studies extend our understanding of CLL pathobiology, demonstrating that reduced differentiation capacity may be a consequence of anergy. Epigenetic drugs may offer possibilities to reactivate PRDM1 expression as part of novel differentiation therapy approaches. (Blood. 2014;123(21):3277-3285) IntroductionChronic lymphocytic leukemia (CLL) is a malignancy of B lymphocytes that retain dependency on extracellular stimuli for their survival and behavior. Two major CLL subsets have been identified which arise at distinct stages of B-cell differentiation and are characterized by varying levels of somatic hypermutation of immunoglobulin (Ig) V-genes.1 Importantly, these subsets exhibit very different clinical behavior. CLL with unmutated V-genes (U-CLL) appears to develop from naive B cells of the natural antibody repertoire with specificity for common pathogens and has a significantly worse prognosis compared with CLL with mutated V-genes (M-CLL). [2][3][4][5] Further support for a role of antigen stimulation in CLL is provided by the presence of biased V-gene usage in both subsets and the presence of conserved sequence motifs within the complementarity determining region 3s of CLL-derived B-cell receptors (BCRs).6-8 Putative CLL antigens have been identified, including self-antigens, or antigens derived from common pathogens including viruses, bacteria, and fungi. 9 The idea that BCR signaling is important in CLL is supported by rece...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Variable induction of PRDM1 and differentiation in chronic lymphocytic leukemia is associated with anergy

Duckworth

Glenn

Slupsky

et al. 2014

“…40,41 A well-characterized survival signal from the lymph node microenvironment that has previously been shown to increase resistance of CLL cells to both ABT-737 and ABT-199 is the CD40 ligand/CD40 interaction, which induces the expression of the antiapoptotic Bcl-2 family proteins Bcl-xL , Bfl-1, and Mcl-1 and downregulates the proapoptotic Bcl-2 family proteins Bim and Noxa. 5,7,15,16,42 We now show that BCR engagement represents another important stimulus from the lymph node microenvironment that confers resistance to ABT-199. We also show that this resistance is mediated primarily by induction of Mcl-1, as evidenced by the significant correlation between Mcl-1 protein levels and protection from ABT-199-induced apoptosis, as well as the almost complete lack of protection following Mcl-1 knockdown in primary CLL cells.…”

Section: Discussionmentioning

confidence: 99%

BCR signaling inhibitors differ in their ability to overcome Mcl-1–mediated resistance of CLL B cells to ABT-199

Bojarczuk

Sasi

Gobessi

et al. 2016

101

Key Points• BCR signals induce resistance in CLL cells by upregulating Mcl-1.• SYK inhibitors prevent BCRmediated Mcl-1 induction more effectively than BTK or PI3Kd inhibitors.The Bcl-2 antagonist has demonstrated promising clinical activity in patients with chronic lymphocytic leukemia (CLL). ABT-199 is strongly cytotoxic against unstimulated peripheral blood CLL cells in vitro but is much less effective against CLL cells that have received survival signals from the microenvironment. In particular, stimulation of CLL cells with CD40L results in substantial resistance mediated by induction of the antiapoptotic Bcl-2 family proteins Bcl-xL and Bfl-1. In this study, we investigated whether resistance to ABT-199 can be conferred by B-cell receptor (BCR) stimulation, which is another important survival signal from the leukemic microenvironment. We show that sustained BCR stimulation results in significant ABT-199 resistance, which correlates with induction of the antiapoptotic protein Mcl-1 and less consistently with downregulation of proapoptotic Bmf, Hrk, and Bim EL . A major role for Mcl-1 in conferring ABT-199 resistance is additionally supported by knockdown and enforced expression experiments with primary CLL cells. We further show that SYK, BTK, and phosphatidylinositol 3-kinase d (PI3Kd) inhibitors significantly downregulate Mcl-1, but with different efficacy. Complete Mcl-1 downregulation was consistently achieved only with SYK inhibitors R406 and GS-9973 (entospletinib), whereas the BTK inhibitor ibrutinib and the PI3Kd inhibitor idelalisib in more than half of the cases had only a partial effect. The greater ability of SYK inhibitors to downregulate Mcl-1 correlated with their greater capacity to block BCR-mediated inactivation of GSK-3, a major negative regulator of Mcl-1. The finding that BCR signaling inhibitors differ in their ability to target Mcl-1 is relevant for the design of clinical trials combining these agents with ABT-199. (Blood. 2016;127(25):3192-3201)

“…1,2 A key role in proliferation and survival of CLL cells is played by microenvironmental factors, which in turn trigger multiple signals mediated by cell surface receptors including CD40, toll-like receptor and B-cell receptor (BCR). [3][4][5] The efforts toward a therapeutic intervention, besides the standard chemo-immunotherapy, have recently focused on hyperactive kinases downstream of the BCR, 6,7 with the development of therapeutically promising inhibitors of these enzymes. [8][9][10] Lyn, for instance, a tyrosine kinase belonging to the Src family kinases (SFKs), has been shown to play a crucial role in the onset and progression of CLL.…”

Section: /Cd23mentioning

confidence: 99%

Lyn sustains oncogenic signaling in chronic lymphocytic leukemia by strengthening SET-mediated inhibition of PP2A

Zonta

Pagano

Trentin

et al. 2015

Key Points• Cytosolic HSP90-bound Lyn mediates resistance to apoptosis by strengthening PP2A/SET interaction in CLL cells.• FTY720-analogues antagonizing the PP2A/SET interaction and Lyn inhibitors may provide a therapeutic approach of CLL.Aberrant protein kinase activities, and the consequent dramatic increase of Ser/Thr and -Tyr phosphorylation, promote the deregulation of the survival pathways in chronic lymphocytic leukemia (CLL), which is crucial to the pathogenesis and progression of the disease. In this study, we show that the tumor suppressor protein phosphatase 2A (PP2A), one of the major Ser/Thr phosphatases, is in an inhibited form because of the synergistic contribution of 2 events, the interaction with its physiologic inhibitor SET and the phosphorylation of Y307 of the catalytic subunit of PP2A. The latter event is mediated by Lyn, a Src family kinase previously found to be overexpressed, delocalized, and constitutively active in CLL cells. This Lyn/PP2A axis accounts for the persistent high level of phosphorylation of the phosphatase's targets and represents a key connection linking phosphotyrosine-and phosphoserine/threonine-mediated oncogenic signals.The data herein presented show that the disruption of the SET/PP2A complex by a novel FTY720-analog (MP07-66) devoid of immunosuppressive effects leads to the reactivation of PP2A, which in turn triggers apoptosis of CLL cells. When used in combination with SFK inhibitors, the action of MP07-66 is synergistically amplified, providing a new option in the therapeutic strategy for CLL patients. (Blood. 2015;125(24):3747-3755) IntroductionChronic lymphocytic leukemia (CLL), the most common leukemia in the Western world, is characterized by the proliferation of CD5 1 / CD19 1 /CD231 B lymphocytes in lymphoid tissues and bone marrow, which progressively accumulate as mature quiescent cells in the peripheral blood. 1,2 A key role in proliferation and survival of CLL cells is played by microenvironmental factors, which in turn trigger multiple signals mediated by cell surface receptors including CD40, toll-like receptor and B-cell receptor (BCR). [3][4][5] The efforts toward a therapeutic intervention, besides the standard chemo-immunotherapy, have recently focused on hyperactive kinases downstream of the BCR, 6,7 with the development of therapeutically promising inhibitors of these enzymes. [8][9][10] Lyn, for instance, a tyrosine kinase belonging to the Src family kinases (SFKs), has been shown to play a crucial role in the onset and progression of CLL. In CLL cells, Lyn is overexpressed and distributed into 2 pools, one associated beneath the cell surface and the other bound to an aberrant cytosolic complex, which exhibits the constitutive activation responsible for the phosphorylation of a myriad of protein targets in the cytosol and for the resistance of CLL cells to apoptosis. 11-13Because Lyn-targeting drugs, such as dasatinib, 14,15 have yielded disappointing results in managing CLL, [16][17][18][19] we have recently focused on the substrates of...