Functional and prognostic role of ZAP-70 in chronic lymphocytic leukaemia

Peptide Microarrays for Real-Time Kinetic Profiling of Tyrosine Phosphatase Activity of Recombinant Phosphatases and Phosphatases in Lysates of Cells or Tissue Samples

A high-throughput method for the determination of the kinetics of protein tyrosine phosphatase (PTP) activity in a microarray format is presented, allowing real-time monitoring of the dephosphorylation of a 3-nitro-phosphotyrosine residue. The 3-nitro-phosphotyrosine residue is incorporated in potential PTP substrates. The peptide substrates are immobilized onto a porous surface in discrete spots. After dephosphorylation by a PTP, a 3-nitrotyrosine residue is formed that can be detected by a specific, sequence-independent antibody. The rate of dephosphorylation can be measured simultaneously on 12 microarrays, each comprising three concentrations of 48 clinically relevant peptides, using 1.0-5.0 μg of protein from a cell or tissue lysate or 0.1-2.0 μg of purified phosphatase. The data obtained compare well with solution phase assays involving the corresponding unmodified phosphotyrosine substrates. This technology, characterized by high-throughput (12 assays in less than 2 h), multiplexing and low sample requirements, facilitates convenient and unbiased investigation of the enzymatic activity of the PTP enzyme family, for instance by profiling of PTP substrate specificities, evaluation of PTP inhibitors and pinpointing changes in PTP activity in biological samples related to diseases.

Real-Time Monitoring of the Dephosphorylating Activity of Protein Tyrosine Phosphatases Using Microarrays with 3-Nitrophosphotyrosine Substrates

Phosphatases and kinases regulate the crucial phosphorylation post-translational modification. In spite of their similarly important role in many diseases and therapeutic potential, phosphatases have received arguably less attention. One reason for this is a scarcity of high-throughput phosphatase assays. Herein, a new real-time, dynamic protein tyrosine phosphatase (PTP) substrate microarray assay measuring product formation is described. PTP substrates comprising a novel 3-nitrophosphotyrosine residue are immobilized in discrete spots. After reaction catalyzed by a PTP a 3-nitrotyrosine residue is formed that can be detected by specific, sequence-independent antibodies. The resulting microarray was successfully evaluated with a panel of recombinant PTPs and cell lysates, which afforded results comparable to data from other assays. Its parallel nature, convenience, and low sample requirements facilitate investigation of the therapeutically relevant PTP enzyme family.

Optimization of flow cytometric measurement of ZAP-70 in chronic lymphocytic leukemia

BACKGROUND

The goal of this study was to optimize a cell staining procedure for flow cytometric detection of zeta-chain associated protein-70 (ZAP-70). Our specific objectives were to improve antibody selection criteria, identify a cell permeabilization procedure better tailored to ZAP-70 analysis, as well as to establish objective criteria to control antigen stability.

METHODS

Sequentially titrated 2F3.2-FITC, 1E7.2-FITC, and 1E7.2-Alexa Fluor 488 anti-ZAP-70 antibodies were used to stain normal B and T cells and Scatchard analysis was applied to calculate K(d) and B(max) values from saturation curves of specific binding. ZAP-70 staining was compared in cells permeabilized with two commercially available kits, Triton X-100, and a custom saponin procedure.

RESULTS

Normal B-cells were found to provide an excellent measure of nonspecific staining while varying ZAP-70 antibodies and concentrations. Comparing Scatchard analyses of specific T-cell binding revealed that 1E7.2-Alexa Fluor 488 had the highest binding affinity of the tested anti-ZAP-70 antibodies and was the best choice. The highest levels of ZAP-70 fluorescence occurred when cells were permeabilized using a noncommercial saponin procedure. Decrease of chronic lymphocytic leukemia cell viability correlated with diminished ZAP-70 expression; when viability was lower than 95% the percentage of bright positive samples was significantly decreased, indicating a possibility of false-negative results.

CONCLUSIONS

The efficiency and reliability of flow cytometric detection of ZAP-70 can be optimized by using Scatchard analysis to help select the most effective antibodies and antibody concentrations that maximize specific to nonspecific binding, by using a "custom" ZAP-70 permeabilization procedure, and by better controlling antigen stability by measuring cell viability.

The effects of non-genomic glucocorticoid mechanisms on bodily functions and the central neural system. A critical evaluation of findings

Mounting evidence suggests that--beyond the well-known genomic effects--glucocorticoids affect cell function via non-genomic mechanisms. Such mechanisms operate in many major systems and organs including the cardiovascular, immune, endocrine and nervous systems, smooth and skeletal muscles, liver, and fat cells. Non-genomic effects are exerted by direct actions on membrane lipids (affecting membrane fluidity), membrane proteins (e.g. ion channels and neurotransmitter receptors), and cytoplasmic proteins (e.g. MAPKs, phospholipases, protein kinases, etc.). These actions are mediated by the glucocorticoids per se or by the proteins dissociated from the liganded glucocorticoid receptor complex. The MR and GR also activate non-genomic mechanisms in certain cases. Some effects of glucocorticoids are shared by a variety of steroids, whereas others are more selective. Moreover, "ultra-selective" effects-mediated by certain glucocorticoids only-were also shown. Disparate findings suggest that non-genomic mechanisms also show "demand-specificity", i.e. require the coincidence of two or more processes. Some of the non-genomic mechanisms activated by glucocorticoids are therapeutically relevant; moreover, the "non-genomic specificity" of certain glucocorticoids raises the possibility of therapeutic applications. Despite the large body of evidence, however, the non-genomic mechanisms of glucocorticoids are still poorly understood. Criteria for differentiating genomic and non-genomic mechanisms are often loosely applied; interactions between various mechanisms are unknown, and non-genomic mechanism-specific pharmacological (potentially therapeutic) agents are lacking. Nevertheless, the discovery of non-genomic mechanisms is a major breakthrough in stress research, and further insights into these mechanisms may open novel approaches for the therapy of various diseases.

Prognostic markers in chronic lymphocytic leukaemia

Rai and Binet staging of chronic lymphocytic leukaemia (CLL) is being superseded by new prognostic markers. The mutational status of the immunoglobulin variable region heavy-chain genes segregates the disease into more benign and more malignant versions, and has been confirmed as an important prognostic marker in prospective clinical trials. A search for surrogate markers for this difficult-to-perform assay has led to flow cytometric assays for CD38 and ZAP-70 expression, although in both cases there are problems with standardization and interpretation of the assays. A separate pathway of research has revealed two chromosomal aberrations--deletions of 11q and 17p--as important prognostic markers. Fluorescent in-situ hybridization has made their detection readily available. These five markers are in different stages of evaluation, but some of them are ready to be used for risk-adapted therapy in clinical trials. Other assays are in earlier stages of assessment.

CD38 and ZAP-70 are functionally linked and mark CLL cells with high migratory potential

Our interest in chronic lymphocytic leukemia (CLL) derives primarily from the exploitation of human diseases as strategic models for defining the in vivo biological roles of CD38. Using this model, we showed that CD38 triggers robust proliferation/survival signals modulated through the interactions with the CD31 ligand expressed by nurse-like cells and by the stromal/endothelial components. By analyzing a cohort of 56 patients with clinically and molecularly characterized CLL, we show that (1) patients with CD38(+)/ZAP-70(+) are characterized by enhanced migration toward Stromal derived factor-1alpha (SDF-1alpha)/CXCL12; (2) CD38 ligation leads to tyrosine phosphorylation of ZAP-70, showing that these markers are functionally linked; (3) ZAP-70 represents a limiting factor for the CD38 pathway in the CLL context, as shown by studying CD38-mediated signal transduction in 26 molecularly characterized patients; and (4) the CLL subgroup of patients defined on the basis of migratory potential is marked by a specific genetic signature, with a significant number of differentially expressed genes being involved in cell-cell interactions and movement. Altogether, the results of this work provide biological evidence for why the combined analysis of CD38 and ZAP-70 expression as determined in several clinical trials results in more dependable identification of patients with CLL who have aggressive disease.

Lipoprotein Lipase mRNA Expression in Whole Blood Is a Prognostic Marker in B Cell Chronic Lymphocytic Leukemia

Background: Chronic lymphocytic leukemia (CLL) is characterized by high individual variability in clinical course and the need for therapy. Differentiation of prognostic subgroups is based primarily on the mutation status of the genes for the variable region of the immunoglobulin heavy chain (IGHV). The time- and labor-intensive nature of this analysis necessitates the use of easily applicable surrogate markers.

Methods: We developed a quantitative PCR (qPCR) method for determining lipoprotein lipase (LPL) mRNA expression and analyzed samples of lysed whole blood and CD19-selected cells from 50 CLL patients. Associations of LPL and ZAP70 [ζ-chain (TCR) associated protein kinase 70 kDa] expression with IGHV mutation status, overall survival (OS), and treatment-free survival (TFS) were investigated.

Results: Lysed samples of whole blood and CD19-selected cells were similar with respect to LPL expression (R = 0.88; P <0.0001). LPL expression was significantly associated with IGHV mutation status [χ2(1) = 15.3; P <0.0001] and showed an 89.3% specificity, a 68.2% sensitivity, an 83.3% positive predictive value, and a 78.1% negative predictive value for IGHV mutation status. LPL expression was significantly associated with both OS and TFS in log-rank tests (both P values = 0.002). LPL-positive patients had a significantly shorter median TFS time (23 months) than LPL-negative patients (88 months) (P = 0.002).

Conclusions: LPL mRNA expression is a valuable prognostic marker in CLL. The method does not require cell purification, and its applicability with archived samples facilitates its use in the clinical routine and other studies.

Feasibility of an easily applicable method of ZAP-70 measurement in chronic lymphocytic leukemia in the routine flow cytometry setting: A methodological approach

Zeta-associated protein 70 (ZAP-70), determined by flow cytometry, has been advocated a surrogate marker of immunoglobulin (Ig)V(H) unmutated status in B chronic lymphocytic leukemia (CLL). The aim of the current study was to test the applicability of an easy flow cytometry protocol for ZAP-70 measurement in CLL samples. Samples from 61 CLL patients and 44 normal subjects were analyzed using a commercial ZAP-70 monoclonal antibody (1E7.2 clone) conjugated with phycoerythrin (PE) and Alexa 488 fluorochromes. Modifications of the published methods led to the structure of a simplified in-house method of ZAP-70 measurement. A three-color approach was used with CD19, CD3 gating comparing with the isotype control provided by the same manufacturer. The cutoff levels for ZAP-70 positivity were defined from a receiver operator characteristic curve in relation to the IgV(H) mutational status and from the ln normalized mean value +2 SD of normal controls. Using the 20% cutoff value for ZAP-70 positivity in CLL patients defined by the literature, ZAP-PE had a sensitivity of 55% and a specificity of 98% in predicting the IgV(H) mutational status, whereas the corresponding values for ZAP-Alexa were 55% and 84%, respectively. Using the 7% cutoff value for CD38 positivity, the sensitivity was 55%, whereas the specificity was 76%. ZAP-70-positive patients showed a shorter time to disease progression in comparison with ZAP-70-negative patients (p < 0.001). In conclusion, the 100% specific prediction of mutational status is accompanied by reduced sensitivity, thus limiting ZAP-70's applicability either as a single marker or combined with CD38 for the assessment of the mutational status of CLL.

In-tandem insight from basic science combined with clinical research: CD38 as both marker and key component of the pathogenetic network underlying chronic lymphocytic leukemia

The absence of mutations in the IgV genes, together with the presence of ZAP-70 and CD38, are the most reliable negative prognostic markers for chronic lymphocytic leukemia (CLL) patients. Several lines of evidence indicate that CD38 may be not only a diagnostic marker but also a key element in the pathogenetic network in CLL. First, CD38 is a receptor that induces proliferation and increases survival of CLL cells. Second, CD38 signals start upon interaction with the CD31 ligand expressed by stromal and nurse-like cells. Third, CD38/CD31 contacts up-regulate CD100, a semaphorin involved in sustaining CLL growth. Fourth, evidence that nurselike cells express high levels of CD31 and plexin-B1, the high-affinity ligand for CD100, offers indirect confirmation for this model of receptor cross-talk. Elements of variation in the clinical course of CD38(+) CLL patients include (1) potential intersection with ZAP-70, a kinase involved in the CD38 signaling pathway in T and natural killer (NK) cells, and (2) the effects of genetic polymorphisms of the receptors involved, at least of CD38 and CD31. Consequently, CD38 together with ZAP-70 appear to be the key elements of a coreceptor pathway that may sustain the signals mediated by the B-cell receptor and potentially by chemokines and their receptors. This would result in acquisition of increased survival potential, providing clues to the poorer prognosis of CD38(+) patients.

Kolmogorov–Smirnov statistical test for analysis of ZAP-70 expression in B-CLL, compared with quantitative PCR and IgVH mutation status

BACKGROUND

ZAP-70 has been proposed as a surrogate marker for immunoglobulin heavy-chain variable region (IgV(H)) mutation status, which is known as a prognostic marker in B-cell chronic lymphocytic leukemia (CLL). The flow cytometric analysis of ZAP-70 suffers from difficulties in standardization and interpretation. We applied the Kolmogorov-Smirnov (KS) statistical test to make analysis more straightforward.

METHODS

We examined ZAP-70 expression by flow cytometry in 53 patients with CLL. Analysis was performed as initially described by Crespo et al. (New England J Med 2003; 348:1764-1775) and alternatively by application of the KS statistical test comparing T cells with B cells. Receiver-operating-characteristics (ROC)-curve analyses were performed to determine the optimal cut-off values for ZAP-70 measured by the two approaches. ZAP-70 protein expression was compared with ZAP-70 mRNA expression measured by a quantitative PCR (qPCR) and with the IgV(H) mutation status.

RESULTS

Both flow cytometric analyses correlated well with the molecular technique and proved to be of equal value in predicting the IgV(H) mutation status. Applying the KS test is reproducible, simple, straightforward, and overcomes a number of difficulties encountered in the Crespo-method.

CONCLUSIONS

The KS statistical test is an essential part of the software delivered with modern routine analytical flow cytometers and is well suited for analysis of ZAP-70 expression in CLL.

A standardized ZAP-70 assay—Lessons learned in the trenches

BACKGROUND

The disease of chronic lymphocytic leukemia (CLL) has been shown to exhibit varying clinical outcomes based on reported laboratory parameters. One of these parameters involves the measurement of the protein levels of zeta-associated protein (ZAP-70) in CLL cells. A standardized assay has not yet reached consensus in the clinical cytometry community.

METHODS

We developed a system using the 8-peak Rainbow beads as our fluorescence calibrator along with a fixed cell control. Using a panel of CD19-PE, CD5-FITC, and ZAP-70-Alexa 647, we stained normal whole blood, and blood and bone marrow from patients with CLL to determine the level of ZAP-70 expression in T-cell, B-cell, and CLL-cell populations. ZAP-70 expression was reported in molecules equivalent fluorescence (MEFL) based on the calibration of the flow cytometer with the 8-peak Rainbow beads.

RESULTS

Daily assay performance as well as operating MEFL defined ranges for ZAP-70 detection in CLL were developed. A rank-order, nonparametric approach to reference ranges was used to assign a cutoff for "negative" as well as ranges for "intermediate" and "positive" staining using T and B cells from a pool of 50 normal subjects, and CLL cells from 395 patients. The assay was validated in a multi-institutional study and has demonstrated correlation with published techniques. Since its initial development, the assay has been implemented at two additional laboratory sites and has been shown to produce reproducible, correlated data at all sites.

CONCLUSIONS

Strict adherence to standardization can yield an assay that is predictable, reliable, and reproducible as well as capable of multisite implementation. The Rainbow beads provide a common platform for system calibration. The fixed cell culture controls provide a common target to test antibody. The final level of control tests the sensitivity of ZAP-70 detection in a normal peripheral blood sample stained along with the submitted CLL patients. The acceptance/rejection of test results must meet all three levels of control before patient results are reported.

Comparison of methods for determining zeta-chain associated protein – 70 (ZAP-70) expression in patients with B-cell chronic lymphocytic leukemia (B-CLL)

BACKGROUND

Zeta-chain associated protein of 70kDa (ZAP-70) is the most promising surrogate marker for the immunoglobulin heavy chain variable region (IgV(H)) mutation status in B-cell chronic lymphocytic leukemia (B-CLL). Crespo et al. proposed the detection of ZAP-70 by flow cytometry. Recently several novel monoclonal antibodies appeared on market.

METHODS

We compared different staining methods utilizing monoclonal antibodies (moAb) against ZAP-70: anti-ZAP-70 PE, clone 1E7.2, anti-ZAP-70 PE, clone 17A/P-ZAP70 directly stained with flourochrome as well as anti-ZAP-70 antibody, clone 2F3.2 stained with Zenontrade mark Alexa Fluor(R) 488 Labeling Kit. Additionally different reagents for permeabilization such as IntraPrep, FIX & PERM, Perm/Wash and 70% ethanol/paraformaldehyde were used to find the most clinically relevant and easy assay to determine ZAP-70 expression in B-CLL. Moreover we compared results of ZAP-70 expression assessed by whole blood protocol with those obtained using-peripheral mononuclear cells isolated from whole blood.

RESULTS

Anti-ZAP-70 moAb clone 17A/P-ZAP70 gave elevated results for all B-CLL patients as well as healthy controls. Staining with anti-ZAP-70 moAb clone 1E7.2 and anti-ZAP-70 moAb clone 2F3.2 was effective in distinguishing negative and positive cells for ZAP-70 protein expression. Not statistically significant discrepancies of ZAP-70 expression were noticed between different fixation and permeabilization methods.

CONCLUSION

Basing on results obtained during this study we can recommend use of anti-ZAP-70 PE, clone 1E7.2 moAb utilizing whole blood protocol with commercial kits for permeabilization as an easy method that brings compatible results to the original method proposed by Crespo et al.