Transient transfection of human peripheral blood basophils

Identifying regulatory pathways of spleen tyrosine kinase expression in human basophils

BACKGROUND

Expression levels of spleen tyrosine kinase (SYK), a critical signaling tyrosine kinase in basophils, are uniquely low relative to all other circulating leukocytes, and levels are highly variable in the population.

OBJECTIVE

We sought to determine whether transcriptional regulation of SYK through unique silencing of the SYK gene determines its basophil-specific expression patterns.

METHODS

Culture-derived basophils (CD34B cells) were derived from cultures of CD34⁺ progenitor cells by using 2 methods (G1 or G3). Peripheral blood basophils (PBBs; relative SYK protein level = 1), B cells (SYK = 8), CD34B-G1 cells (SYK = 11), and CD34B-G3 cells (SYK = 5) were examined by using assay for transposase-accessible chromatin sequencing (ATAC-seq) methods. In addition, the transcriptomes of 6 cell types, PBBs, peripheral blood eosinophils (SYK = 11), plasmacytoid dendritic cells (SYK = 30), CD34⁺ progenitors (SYK = 11), CD34B-G1 cells, and CD34B-G3 cells, were analyzed for patterns that matched patterns of SYK expression in these cells, with a focus on transcription factors.

RESULTS

ATAC-seq showed that PBBs have multiple open regions in the SYK gene, suggesting a nonsilenced state with 1 region unique to PBBs (low SYK expression), 1 region unique to both PBBs (low SYK expression) and both G1 and G3 CD34B cells (high and moderate SYK expression, respectively), and 5 regions unique to B cells (high SYK expression). SYK expression across the 6 cell types explored showed a unique pattern that was matched to expression patterns of 3 transcription factors: Kruppel-like factor 5 (KLF5), zinc-finger protein 608 (ZNF608), and musculoaponeurotic fibrosarcoma protein (c-MAF).

CONCLUSIONS

Two new potential regulatory pathways for SYK expression were identified. One appears independent of transcriptional regulation, and one appears to be dependent on transcriptional control in the SYK gene.

History of Histamine-Releasing Factor (HRF)/Translationally Controlled Tumor Protein (TCTP) Including a Potential Therapeutic Target in Asthma and Allergy

Histamine-releasing factor (HRF) also known as translationally controlled tumor protein (TCTP) is a highly conserved, ubiquitous protein that has both intracellular and extracellular functions. Here we will highlight the subcloning of the molecule, its clinical implications, as well as an inducible-transgenic mouse. Particular attention will be paid to its extracellular functioning and its potential role as a therapeutic target in asthma and allergy. The cells and the cytokines that are produced when stimulated or primed by HRF/TCTP will be detailed as well as the downstream signaling pathway that HRF/TCTP elicits. While it was originally thought that HRF/TCTP interacted with IgE, the finding that cells not binding IgE also respond to HRF/TCTP called this interaction into question. HRF/TCTP or at least its mouse counterpart appears to interact with some, but not all IgE and IgG molecules. HRF/TCTP has been shown to activate multiple human cells including basophils, eosinophils, T cells, and B cells. Since many of the cells that are activated by HRF/TCTP participate in the allergic response, the extracellular functions of HRF/TCTP could exacerbate the allergic, inflammatory cascade. Particularly exciting is that small molecule agonists of the phosphatase SHIP-1 have been shown to modulate the P13 kinase/AKT pathway and may control inflammatory disorders. This review discusses this possibility in light of HRF/TCTP.

Autoantibodies to IgE and FcεRI and the natural variability of spleen tyrosine kinase expression in basophils

BACKGROUND

Secretion from human basophils and mast cells requires spleen tyrosine kinase (SYK) activity, but SYK expression is highly variable in the general population, and this variability predicts the magnitude of IgE-mediated secretion. One known mechanism of modulating SYK expression in human basophils is aggregation of FcεRI.

OBJECTIVE

This study examines the possibility that functional autoantibodies are present in a wide variety of subjects and, in particular, subjects whose basophils poorly express SYK. It also tests whether any found antibodies could modulate SYK expression in maturing basophils and whether interaction with FcγRIIb/CD32b modulates the effect.

METHODS

An experimental algorithm for classifying the nature of histamine release induced by serum from 3 classes of subjects was developed.

RESULTS

The frequency of functional autoantibodies that produce characteristics concordant with FcεRI-mediated secretion was zero in 34 subjects without chronic spontaneous urticaria (CSU). In patients with CSU, the frequency was lower than expected, approximately 7%. For the 5 of 68 unique sera from patients with CSU tested that contained anti-FcεRI or anti-IgE antibodies, these antibodies were found to induce downregulation of SYK in both peripheral blood basophils and basophils developed from CD34⁺ progenitors. Blocking interaction of these antibodies with CD32b did not alter their ability to downregulate SYK expression.

CONCLUSIONS

This study establishes that functional autoantibodies to IgE/FcεRI do not provide a good explanation for the variability in SYK expression in basophils in the general population. They do show that if antibodies with these characteristics are present, they are capable of modulating SYK expression in developing basophils.

Pros and Cons of Clinical Basophil Testing (BAT)

PURPOSE OF REVIEW

We review basophil testing by flow cytometry with an emphasis on advantages and disadvantages.

RECENT FINDINGS

There are many tools available to assess the presence and severity of allergic diseases in patients. For 50 years, peripheral blood basophils have been used as tools to study these diseases. It is a very accessible cell that binds IgE antibody and secretes the classical mediators responsible for the symptoms of allergic reactions. In the last decade, an even more accessible methodology, using flow cytometry, has been developed to enhance the ability to use basophils for both mechanistic and clinical diagnostics. Basophil testing has been included in diagnostics for different forms of allergies as well as to monitor disease status. A variety of studies have begun to establish both precise methods and their clinical relevance for disease diagnosis, but there remain some important questions on how to take optimal advantage of the behaviours of basophils.

Gene silencing approaches in mast cells and primary human basophils

The ability to silence gene expression is an invaluable tool for elucidating the importance of intracellular signaling proteins which contribute to the effector functions of mast cells and basophils. However, primary mast cells and their terminally differentiated blood counterpart, namely basophils, pose a difficult challenge for gene silencing approaches given not only their state of maturation and difficulty to transfect, but also because their functions are readily altered by cell-handling conditions. Here, we describe a method using lipofection which has been successfully employed to silence gene expression using siRNA in human LAD2 mast cells as well as primary human basophils.

Potential role of histamine releasing factor (HRF) as a therapeutic target for treating asthma and allergy

Histamine releasing factor (HRF), also known as translationally controlled tumor protein (TCTP), is a highly conserved, ubiquitous protein that has both intracellular and extracellular functions. Here, we will highlight the history of the molecule, its clinical implications with a focus on its extracellular functioning, and its potential role as a therapeutic target in asthma and allergy. The cells and cytokines produced when stimulated or primed by HRF/TCTP are detailed as well as the downstream signaling pathway that HRF/TCTP elicits. While it was originally thought that HRF/TCTP interacted with IgE, the finding that cells not binding IgE also respond to HRF/TCTP called this interaction into question. HRF/TCTP, or at least its mouse counterpart, appears to interact with some, but not all IgE and IgG molecules. HRF/TCTP has been shown to activate multiple human cells including basophils, eosinophils, T cells, and B cells. Since many of the cells activated by HRF/TCTP participate in the allergic response, extracellular functions of HRF/TCTP may exacerbate the allergic, inflammatory cascade. Particularly exciting is that small molecule agonists of Src homology 2-containing inositol phosphatase-1 have been shown to modulate the phosphoinositide 3-kinase/AKT pathway and may control inflammatory disorders. This review discusses this possibility in light of HRF/TCTP.

Early signal protein expression profiles in basophils: a population study

IgE-mediated histamine release from peripheral blood basophils is highly variable within the general population. Recent studies have shown that the ability of anti-IgE antibody to induce release can be predicted reasonably well by knowing the level of syk expression in the cells. The current study expands a previous survey to include 14 additional early elements known to be involved in activation and deactivation of basophils and showed that with the exception of syk, the variance of expression of 19 other elements (lyn, fyn, csk, cbp/PAG, CIN85, Bob1, c-cbl, SHIP1, SHIP2, p85alpha, p110delta, btk, PLCgamma1, PLCgamma2, SHP-1, PTEN, SOS2, CRACM1, and IL-3Ralpha) was narrow despite a broad range of functional capability in the basophils under study. With syk as the only element with high variance and well-correlated to maximum histamine release and cellular sensitivity, this survey examined the expression levels of two proteins thought to regulate syk expression: Bob1/OCA-B and CIN85. Expression of CIN85 was not correlated to syk expression, but Bob1 expression was negatively correlated to expression of syk and maximum histamine release. However, the expected behavior for this protein should have been as a protector of post-translational syk loss and therefore, positively correlated. Previous studies suggested that post-translational control mechanisms regulated syk expression. However, in this study, steady-state mRNA levels for syk in resting basophils showed a correlation with syk protein expression levels (r=0.593). It is concluded that with the exception of syk expression, the expression of 19 early signaling elements is tightly regulated and that a component of the regulation of syk may be related to control of transcription or processing of syk mRNA.

Histamine-releasing factor/translationally controlled tumor protein (HRF/TCTP)-induced histamine release is enhanced with SHIP-1 knockdown in cultured human mast cell and basophil models

Previously, we demonstrated a negative correlation between histamine release to histamine-releasing factor/translationally controlled tumor protein (HRF/TCTP) and protein levels of SHIP-1 in human basophils. The present study was conducted to investigate whether suppressing SHIP-1 using small interfering (si)RNA technology would alter the releasability of culture-derived mast cells and basophils, as determined by HRF/TCTP histamine release. Frozen CD34+ cells were obtained from the Fred Hutchinson Cancer Research Center (Seattle, WA, USA). Cells were grown in StemPro-34 medium containing cytokines: mast cells with IL-6 and stem cell factor (100 ng/ml each) for 6-8 weeks and basophils with IL-3 (6.7 ng/ml) for 2-3 weeks. siRNA transfections were performed during Week 6 for mast cells and Week 2 for basophils with siRNA for SHIP-1 or a negative control siRNA. Changes in SHIP-1 expression were determined by Western blot. The functional knockdown was measured by HRF/TCTP-induced histamine release. siRNA knockdown of SHIP-1 in mast cells ranged from 31% to 82%, mean 65 +/- 12%, compared with control (n=4). Histamine release to HRF/TCTP was increased only slightly in two experiments. SHIP-1 knockdown in basophils ranged from 34% to 69%, mean 51.8 +/- 7% (n=4). Histamine release to HRF/TCTP in these basophils was dependent on the amount of SHIP knockdown. Mast cells and basophils derived from CD34+ precursor cells represent suitable models for transfection studies. Reducing SHIP-1 protein in cultured mast cells and in cultured basophils increases releasability of the cells.

Inducing an anergic state in mast cells and basophils without secretion

BACKGROUND

IgE-mediated secretion from mast cells or basophils depends on the activity of both spleen tyrosine kinase (syk) and phosphatidyl inositol 3' kinase (PI3K), but several specific downregulatory pathways (eg, loss of syk expression) do not.

OBJECTIVE

We tested whether stimulation with antigen in the presence of a syk inhibitor (NVP-QAB205) would ablate secretion while simultaneously allowing anergy.

METHODS

The anergic or desensitized state in human basophils, cultured-derived mast cells, and in situ stimulated airway mast cells (in organ baths) was assessed after stimulation with antigen in the presence of syk inhibitor.

RESULTS

Antigen caused 35 +/- 7% and 62 +/- 10% histamine release from basophils and mast cells, respectively, and it caused an 87 +/- 5% histamine/leukotriene D(4)-dependent contraction of human isolated bronchi. All of these responses were blocked >95% by the syk inhibitor. Rechallenging the preparations with antigen, after first washing out the syk inhibitor and antigen, revealed that near complete anergy (92% to 100%) occurred in each case. A similar result was found when using a PI3K inhibitor, LY294002, in studies of basophils.

CONCLUSION

Although the syk inhibitor nearly abolished the antigen-induced secretion from mast cells and basophils, it had little effect on the pathways involved in anergy. These results suggest that syk and PI3K are not involved in downregulation leading to anergy.

Induced loss of Syk in human basophils by non-IgE-dependent stimuli

In the general population, Syk expression in human basophils is highly variable and correlates well with the IgE-mediated responsiveness of these cells. Previous studies established that IgE-mediated stimulation results in loss of Syk expression. The current studies investigated whether stimulation through other receptors results in loss of Syk. Two classes of stimulation were examined, those that operate through the kinase Syk and those that operate through a GTP-binding protein. These studies demonstrated that aggregation of leukocyte Ig-like receptor LILRA-2 resulted in phosphorylation of Syk and c-Cbl, was inhibited by a third generation Syk inhibitor with an expected IC(50), and induced histamine release in strict proportion to release induced by anti-IgE Ab. Stimulation of LILRA-2 for 18 h resulted in modest loss of Syk that correlated with the more profound loss of Syk induced by anti-IgE Ab. Human recombinant histamine-releasing factor has also recently been shown to induce Syk phosphorylation and in the current studies has also been shown to induce loss of Syk in 18-h cultures. fMLP stimulation for 18 h was also found to induce modest loss of Syk. fMLP induced phosphorylation of c-Cbl that was sustained for at least 45 min. Phosphorylation of c-Cbl was inhibited by a Syk kinase inhibitor but with an IC(50) that was not consistent with Syk activity, suggesting another kinase was responsible for Cbl phosphorylation following fMLP. These studies demonstrate that it is possible to induce the loss of Syk expression in human basophils by a non-IgE-dependent mechanism and even by a mechanism that does directly involve Syk in the reaction complex.

Relationship between spleen tyrosine kinase and phosphatidylinositol 5' phosphatase expression and secretion from human basophils in the general population

BACKGROUND

Previous studies have suggested that expression levels of spleen tyrosine kinase (syk) or phosphatidylinositol 5' phosphatase (SHIP) may explain certain extreme human basophil phenotypes.

OBJECTIVE

This study is designed to explore whether variability in syk and SHIP expression levels in the general population, alone or in concert, can account for the variability in basophil function.

METHODS

A survey of maximum responsiveness to IgE-mediated stimulation, sensitivity, and expression levels of 6 early signaling elements was performed on 36 subjects' basophils.

RESULTS

Of the 6 signaling elements, only syk and SHIP showed a correlation with maximum histamine release or cellular sensitivity. In a multiple regression, syk and SHIP together could account for 67% of population variance, although most of the variance was explained by syk expression. The pattern of expression variance syk>>SHIP1>SHIP2 approximately lyn approximately p85 approximately cbl suggested a process that primarily modulated syk levels. IL-3 is known to modulate syk levels, but we found that a 3-day incubation with IL-3 resulted in increased expression of other signaling elements to a greater degree: cbl>SHIP1>SHIP2 approximately lyn approximately p85 > or = syk, opposite the pattern in the population survey. In contrast, 18-hour stimulation with anti-IgE antibody led to marked downregulation of syk expression, modest downregulation of Fc epsilon RI expression, weak downregulation of lyn expression, and no effect on 23 other signaling elements.

CONCLUSION

Unlike studies in mice, we conclude that expression of syk is a good preconditioning predictor of basophil function in the general population.

CLINICAL IMPLICATIONS

The finding that expression of syk levels may strongly influence functional responses of basophils suggests a mechanism underlying the severity of atopic diseases.

Acute IL-3 priming up-regulates the stimulus-induced Raf-1-Mek-Erk cascade independently of IL-3-induced activation of Erk

IL-3 is a potent priming cytokine for human basophils, inducing an increase of mediator release after stimulation. The mechanism of IL-3 priming of the basophil response to FcepsilonRI aggregating stimuli remains unknown. We explored the regulation of several elements of IgE-mediated signaling by a short priming with IL-3. Early signaling events such as phosphorylation of Syk, Shc, linker for activation of T cells, and the calcium signal were not statistically affected by acute IL-3 priming. Downstream in the signaling cascade, a point of up-regulation was found at the level of Raf-1-Mek-Erk. Although the phosphorylation of Raf-1 was not changed by IL-3 priming, IL-3-primed anti-IgE-stimulated basophils showed a strong synergism for Mek and Erk phosphorylation when compared with either IL-3 or anti-IgE alone; pre-exposure to IL-3 induced a final 13-fold average increase over anti-IgE-induced Erk phosphorylation (6-fold above the sum of anti-IgE and IL-3 alone). The kinetics, dose response, and pharmacologic characteristics of the IL-3 priming of stimulus-induced Erk phosphorylation support the involvement of a yet unknown mechanism that is independent of IL-3-induced Erk and PI3K activation. This type of preactivation can be mimicked by incubation with the Ser-Thr kinase inhibitors, Ro-81-3220, or bisindoylmaleimide II.