Mimicking the tumour microenvironment of chronic lymphocytic leukaemia in vitro critically depends on the type of B-cell receptor stimulation.

BACKGROUND: The B-cell receptor (BCR) has a key role in the cross-talk between chronic lymphocytic leukaemia (CLL) cells and the tissue microenvironment, which favours disease progression by promoting proliferation and drug resistance. In vitro studies on downstream signalling and functional effects of CLL BCR ligation often report contradictory results, in part owing to the lack of a standardised stimulation protocol. Our aim was to define a biologically relevant and robust in vitro stimulation method with regard to cellular phenotypic and transcriptional responses. METHODS: We evaluated mRNA (FOS, MYC, LPL) and protein (CD54, CD19, CD62L, CD184) expression of genes modulated by BCR triggering in immunoglobulin heavy-chain variable region genes (IGHV)-mutated and -unmutated CLL cells, after stimulation using soluble or immobilised anti-IgM antibodies from different suppliers. RESULTS: The effect of BCR stimulation on gene and protein expression was comparable in all CLL patients, irrespective of IGHV mutation status. However, immobilised anti-IgM stimulation elicited clear and robust changes in gene and protein expression, whereas the response to soluble anti-IgM was far less obvious. CONCLUSIONS: These data indicate that the method of BCR stimulation is of major importance regarding responsiveness of CLL cells in the context of the tumour microenvironment, whereas genetic differences in the BCR pathway are less critical.

Lipoprotein lipase SNPs rs13702 and rs301 correlate with clinical outcome in chronic lymphocytic leukemia patients.

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western world and is characterized by a heterogeneous clinical course. This variability in clinical course has spiked the search for prognostic markers able to predict patient evolution at the moment of diagnosis. Markers demonstrated to be of value are the mutation status of the immunoglobulin heavy chain variable region genes (IGHV) and lipoprotein lipase (LPL) expression. High LPL mRNA expression has been associated with short treatment free (TFS) and decreased overall survival (OS) in CLL. The LPL SNPs rs301 (T

ER stress in diffuse large B cell lymphoma: GRP94 is a possible biomarker in germinal center versus activated B-cell type.

The process of B-cell development is characterized by the activation of the unfolded protein response. Under certain circumstances, the unfolded protein response can be manipulated in a cell death-inducing way. Therefore, tackling the unfolded protein response might be an attractive strategy in the treatment of diffuse large B-cell lymphomas. Our research showed more basal unfolded protein response activity and differences in the inducibility of ER stress in activated B-cell versus germinal center cell lines. Moreover, the diffuse large B cell lymphoma patient data revealed that the glucose-regulated protein 94 is new potential discriminator for diffuse large B cell lymphoma.

Identification of an Ire1alpha endonuclease specific inhibitor with cytotoxic activity against human multiple myeloma.

Activation of the adaptive Ire1-XBP1 pathway has been identified in many solid tumors and hematologic malignancies, including multiple myeloma (MM). Here, we report the identification of STF-083010, a novel small-molecule inhibitor of Ire1. STF-083010 inhibited Ire1 endonuclease activity, without affecting its kinase activity, after endoplasmic reticulum stress both in vitro and in vivo. Treatment with STF-083010 showed significant antimyeloma activity in model human MM xenografts. Similarly, STF-083010 was preferentially toxic to freshly isolated human CD138(+) MM cells compared with other similarly isolated cell populations. The identification of this novel Ire1 inhibitor supports the hypothesis that the Ire1-XBP1 axis is a promising target for anticancer therapy, especially in the context of MM.

The flavonoid tangeretin activates the unfolded protein response and synergizes with imatinib in the erythroleukemia cell line K562.

We explored the mechanism of cell death of the polymethoxyflavone tangeretin (TAN) in K562 breakpoint cluster region-abelson murine leukemia (Bcr-Abl+) cells. Flow cytometric analysis showed that TAN arrested the cells in the G(2)/M phase and stimulated an accumulation of the cells in the sub-G(0) phase. TAN-induced cell death was evidenced by poly(ADP)-ribose polymerase cleavage, DNA laddering fragmentation, activation of the caspase cascade and downregulation of the antiapoptotic proteins Mcl-1 and Bcl-x(L). Pretreatment with the pancaspase inhibitor Z-VAD-FMK_blocked caspase activation and cell cycle arrest but did not inhibit apoptosis which suggest that other cell killing mechanisms like endoplasmic reticulum (ER)-associated cell death pathways could be involved. We demonstrated that TAN-induced apoptosis was preceded by a rapid activation of the proapoptotic arm of the unfolded protein response, namely PKR-like ER kinase. This was accompanied by enhanced levels of glucose-regulated protein of 78 kDa and of spliced X-box binding protein 1. Furthermore, TAN sensitized K562 cells to the cell killing effects of imatinib via an apoptotic mechanism. In conclusion, our results suggest that TAN is able to induce apoptosis in Bcr-Abl+ cells via cell cycle arrest and the induction of the unfolded protein response, and has synergistic cytotoxicity with imatinib.

Xanthohumol activates the proapoptotic arm of the unfolded protein response in chronic lymphocytic leukemia.

BACKGROUND: Chronic lymphocytic leukemia (CLL) is an incurable disease with a natural history of increasing resistance to chemotherapy. A novel approach to overcome chemotherapy resistance may be targeting the endoplasmic reticulum (ER). PATIENTS AND METHODS: The involvement of the unfolded protein response (UPR) in the cell killing effect of xanthohumol (X) was examined in 18 patient samples. RESULTS: X-induced apoptosis of CLL cells was accompanied by the induction of glucose-regulated protein of 78 kDa (GRP78) and heat-shock protein of 70 kDa (Hsp70) protein levels and by sustained phosphorylation of the eukaryotic translation initiation factor 2 (eIF2alpha), suggesting the involvement of the ER stress transducer, the double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK). The X-box-binding protein 1 (XBP1) mRNA was spliced but no clear activation of activating transcription factor 6 (ATF6) was observed. The proapoptotic outcome was further demonstrated by the up-regulation of CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), down-regulation of myeloid cell leukemia 1 (Mcl-1) and B-cell lymphoma 2 (Bcl-2), cleavage of poly-(ADP)-ribose polymerase (PARP) and processing of caspase-3, -4 and -9. Furthermore, X showed proteasome inhibitory activity. CONCLUSION: X stimulates the proapoptotic arm of the UPR in ex vivo CLL cells, suggesting that ER stress may play an important role during X-induced apoptosis.

Chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia remains the most common adult leukaemia in Western countries. In this review we tried to give an overview of the important prognostic markers and the developments in this field. We also reflected about the accumulative character of the disease and the influence of the micro-environment on the CLL cell.

Steroid effects on ZAP-70 and SYK in relation to apoptosis in poor prognosis chronic lymphocytic leukemia.

There is resurgent interest in glucocorticoids (GCs) in the treatment of poor prognosis chronic lymphocytic leukemia (CLL). Little is known however on how GCs induce apoptosis in CLL. Methylprednisolone (MP) induces apoptosis in ZAP-70 positive CLL more readily than in ZAP-70 negative CLL, which is in contrast to the effects of radiation and chemotherapy. The increased GC sensitivity of ZAP-70+ CLL was studied in relation to the expression status of ZAP-70 and the related signal transducing tyrosine kinase SYK. Both ZAP-70 and SYK were downregulated by GC treatment. Moreover, SYK was dephosphorylated by the phosphatase PTP1B of which the expression and translation levels were induced by GCs. Inhibition of PTP1B successfully restored ZAP-70 expression and SYK phosphorylation but did not interfere with GC-induced apoptosis. Therefore, the downregulation of ZAP-70 and P-SYK per se during treatment with GCs is not sufficient to induce apoptosis, and different mechanisms must therefore be responsible for the increased steroid sensitivity of ZAP-70+ CLL.

The microbial PhIP metabolite 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1) induces DNA damage, apoptosis and cell cycle arrest towards Caco-2 cells.

7-Hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1) is a newly identified intestinal microbial metabolite from the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Although the mutagenic potential of the endogenous N-hydroxy PhIP derivate has been reported, the risks associated with PhIP-M1 have not yet been explored. In this work, the cytotoxic and genotoxic effects originating from PhIP-M1 were assessed in the epithelial intestinal Caco-2 cell line. PhIP-M1 significantly decreased in a time- and dose-dependent manner mitochondrial dehydrogenase activity and protein synthesis, with IC50 values of, respectively, 180+/-39.4 and 173+/-20.3 microM after 24h, and 33.8+/-3.5 and 37.3+/-10.9 microM after 72 h. Apoptosis within the concentration ranges of cytotoxicity was confirmed by morphological examination, DAPI nuclear staining and annexin V staining. PhIP-M1 provoked cell cycle arrest, characterized by a significant increase in the number of nucleoids in the G2/M phase. A dose-dependent increase in DNA damage, as quantified by the alkaline comet assay, was observed after 3h in the 50-200 microM range. Because these PhIP-M1-induced genomic and cellular events may contribute to the carcinogenicity of PhIP, the potency of the colon microbiota to bioactivate PhIP must be included in future risk assessments.

Review. The endoplasmic reticulum: a target for new anticancer drugs.

In eukaryotic cells, the endoplasmic reticulum (ER) is the principal site for the folding and maturation of transmembrane, secretory and ER-resident proteins. Functions of the ER are affected by various intracellular and extracellular stimuli, which include inhibition of glycosylation, reduction of disulfide bonds, calcium depletion from the ER lumen, impairment of protein transport to the Golgi, and expression of mutated proteins in the ER. Under ER stress, unfolded/misfolded proteins accumulate in the ER lumen, which induces conflicting cellular activities: survival and apoptosis. To cope with this stress, cells activate intracellular signalling pathways, such as the unfolded protein response (UPR) and the ER-associated degradation (ERAD). However, under conditions of severe ER stress or when the UPR has been compromised, the cell may be incapable of maintaining ER homeostasis, which may eventually activate programmed cell death (PCD) pathways. Clinical data support the potential of drugs that inhibit the normal functions and homeostasis of the ER and the proteasome in treatment of malignancies like cancer. It is therefore reasonable to assume that manipulation of ER stress might enhance the efficacy of chemotherapeutic drugs and provide new anticancer targets like the ER and the proteasome.

Xanthohumol kills B-chronic lymphocytic leukemia cells by an apoptotic mechanism.

B-chronic lymphocytic leukemia (B-CLL) is an indolent lymphoid malignancy with variable prognosis. Adverse prognostic factors comprise treatment resistance, cytogenetics (11q- and 17p-), the presence of unmutated Ig genes, and the more comprehensive activation marker Zap 70. In contrast to diminished sensitivity to chemotherapy, Zap 70+ B-CLL cells retain their responsiveness to manipulation of signal transduction and monoclonals. Xanthohumol (XA) has recently been documented to have an impact on breast cancer cell growth and invasiveness in vitro. Based on these observations, lymphocytes from patients with B-CLL were cultured in the presence of XA in vitro. XA induced a dose-dependent killing of B-CLL cells at an LD(50) ((24 h)) of 24.4 +/- 6.6 microM, independent of known adverse prognostic factors including functional loss of p53. Cell death was associated with poly (ADP)-ribose polymerase cleavage and annexin V positivity, suggestive of an apoptotic mechanism. Surprisingly, p 70(S 6 K) phosphorylation was stimulated upon XA treatment. In conclusion, XA has an antitumor activity on B-CLL cells in vitro. The molecular mechanisms behind this pro-apoptotic effect deserve further investigation.

DRL1, a homolog of the yeast TOT4/KTI12 protein, has a function in meristem activity and organ growth in plants.

The DEFORMED ROOTS AND LEAVES1 (DRL1) gene is single copy in the Arabidopsis genome, and based on overall amino acid similarity and conservation of functional domains, the DRL1 protein is homologous with yeast TOT4/KTI12. TOT4/KTI12 associates with Elongator, a multisubunit complex that binds the RNA polymerase II transcription elongation complex. Recessive mutations at the DRL1 locus caused defective organ formation indicative of disorganized shoot, inflorescence, flower, and root meristems. DRL1 is a putative ATP/GTP binding protein; in addition, calmodulin binding activity was demonstrated in vitro for the C terminus of the DRL1 protein. Phenotypic and genetic data position DRL1 relative to regulatory loci for leaf development, in which it acts early. We identified Arabidopsis homologs for the six Elongator components and hypothesize that DRL1 regulates transcription elongation through a putative plant Elongator. Upregulation of the ANGUSTIFOLIA transcript in the strong drl1-2 allele supports this model.