Patient Heterogeneity in Acute Myeloid Leukemia: Leukemic Cell Communication by Release of Soluble Mediators and Its Effects on Mesenchymal Stem Cells

Abstract

Acute myeloid leukemia (AML) is an aggressive bone marrow malignancy, and non-leukemic stromal cells (including mesenchymal stem cells, MSCs) are involved in leukemogenesis and show AML-supporting effects. We investigated how constitutive extracellular mediator release by primary human AML cells alters proteomic profiles of normal bone marrow MSCs. An average of 6814 proteins (range 6493−6918 proteins) were quantified for 41 MSC cultures supplemented with AML-cell conditioned medium, whereas an average of 6715 proteins (range 6703−6722) were quantified for untreated control MSCs. The AML effect on global MSC proteomic profiles varied between patients. Hierarchical clustering analysis identified 10 patients (5/10 secondary AML) showing more extensive AML-effects on the MSC proteome, whereas the other 31 patients clustered together with the untreated control MSCs and showed less extensive AML-induced effects. These two patient subsets differed especially with regard to MSC levels of extracellular matrix and mitochondrial/metabolic regulatory proteins. Less than 10% of MSC proteins were significantly altered by the exposure to AML-conditioned media; 301 proteins could only be quantified after exposure to conditioned medium and 201 additional proteins were significantly altered compared with the levels in control samples (153 increased, 48 decreased). The AML-modulated MSC proteins formed several interacting networks mainly reflecting intracellular organellar structure/trafficking but also extracellular matrix/cytokine signaling, and a single small network reflecting altered DNA replication. Our results suggest that targeting of intracellular trafficking and/or intercellular communication is a possible therapeutic strategy in AML.

Casein Kinase 2 (CK2): A Possible Therapeutic Target in Acute Myeloid Leukemia

“…CK2 is a regulatory molecule at all three levels of networks [56,61], and the function of CK2 as a regulator of Toll-like receptor 4 (TLR4)-NFκB pathway signaling can be used as an example of how CK2 inhibition influences AML cells through effects on all three levels of networks . The various network effects of TLR4 and its CK2-regulated downstream target NFκB summarized in Figure 1: leukemogenesis/chemosensitivity is thereby modulated through three interacting networks: (i) Cross-talking intracellular signaling pathways (yellow) [9,[12][13][14]16,22,71,[75][76][77][78], (ii) the local extracellular microenvironment (extracellular matrix and cytokines; green) [76,[79][80][81][82][83], and (iii) the cellular network with interactions between the leukemic cells and their neighboring non-leukemic endothelial cells [84,[86][87][88][89][90][91], MSC [80,92,93], osteoblasts [76,94,95] and immunocompetent cells [96][97][98][99][100][101] (all in blue). Thus, the effects of TLR4/NFκB intracellular signaling are modulated by CK2-mediated phosphorylation of the common target NFκB.…”

“…The observations described above are mainly based on studies of the overall AML cell population, but several characteristics of the total hierarchically organized AML cell Targeting of complex biological networks in AML by CK2 inhibition; TLR4/CK2/NFκB interactions as an example of the complexity of CK2 targeting. NFκB is a common target for downstream TLR4 signaling and CK2-mediated phosphorylation; leukemogenesis/chemosensitivity is thereby modulated through three interacting networks: (i) Cross-talking intracellular signaling pathways (yellow) [9,[12][13][14]16,22,71,[75][76][77][78], (ii) the local extracellular microenvironment (extracellular matrix and cytokines; green) [76,[79][80][81][82][83], and (iii) the cellular network with interactions between the leukemic cells and their neighboring non-leukemic endothelial cells [84,[86][87][88][89][90][91], MSC [80,92,93], osteoblasts [76,94,95] and immunocompetent cells [96][97][98][99][100][101] (all in blue). Thus, the effects of TLR4/NFκB intracellular signaling are modulated by CK2-mediated phosphorylation of the common target NFκB.…”

“…TLR4/NFκB signaling is also important for the phenotypic regulation/modulation several nonleukemic AML-supporting stromal cells, including endothelial cells [85][86][87][88][89][90][91], mesenchymal stem cells (MSCs) [80,92,93], osteoblasts [76,94,95], and immunocompetent cells (e.g., monocytes) [96][97][98][99][100]. One would expect CK2 modulation of NFκB to influence the phenotype/function of these non-leukemic cells.…”

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

“…In a recent proteomic study, we investigated the effect of the constitutive AML cell release of soluble mediators on the proteomic profile of normal mesenchymal stem cells (MSCs) [ 35 ]. We observed that the AML effect on the global MSC proteomic profiles differed between patients, and we detected two main AML patient subsets with regard to the AML effect on normal MSCs.…”

“… The constitutive AML cell mediator release cytokine release profile and thereby the context of the TLR4 induced cytokine response will differ between patients [ 24 , 25 , 26 ]. The effect of TLR4 targeting on MSCs/osteoblasts seems to depend on the biological context ( Section 5.1 and Section 5.2 ); due to the functional heterogeneity of AML cells with regard to their constitutive protein release the biological context/microenvironment of the osteoblasts and thereby the effect of TLR4 targeting will differ between AML patients [ 25 , 35 , 45 , 112 , 113 , 114 , 115 , 116 ]. However, although the heterogeneity between patients with regard to constitutive cytokine release by the AML cells may influence the MSC-osteoblast differentiation, the AML supporting MSC effect is observed independent of this patient heterogeneity [ 3 ].…”