English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Peripheral T-cell lymphomas (PTCLs) are among the most aggressive of all lymphomas and are associated with a poor prognosis compared with aggressive B-cell lymphomas. Therefore, novel targeted therapies are needed. Syk is a protein tyrosine kinase involved in B-cell receptor signaling in both normal and malignant B cells.1 Syk activation in B-cell lymphomas is associated with cell growth and survival, and an orally available Syk inhibitor is currently being tested for B-cell lymphomas in a phase I/II clinical trial, with encouraging results.2 Normal T lymphocytes lack Syk expression and use a Syk homolog, Zap-70, in receptor signaling. However, we recently showed that Syk protein is aberrantly expressed in the majority of PTCLs.3 The functional role of Syk in PTCL is currently unknown. Herein, we show that silencing Syk induces apoptosis and blocks proliferation in PTCL cells. These findings suggest that Syk represents a novel therapeutic target for patients with PTCL. To establish an in vitro model for examining the effects of Syk inhibition, we analyzed Syk expression in multiple PTCL cell lines (SeAx, HuT 78, SR-786, Karpas 299 and SU-DHL-1) by both western blot (Figure 1a) and flow cytometry (Figure 1b). Consistent with our previously reported data showing Syk expression in PTCL, three of five cell lines tested (SU-DHL-1, SR-786 and SeAx) showed strong Syk expression.3 Next, we determined the phosphorylation status of Syk in these cell lines. SU-DHL-1 and SR-786 cells, but not SeAx cells, showed Syk phosphorylation at Y348 (Figure 1c and d), a site autophosphorylated on B-cell receptor engagement in B cells.4 Syk was also phosphorylated at Y525/526 in both SU-DHL-1 and SR-786 (data not shown). To determine whether Syk contributes to the growth and survival of T-cell lymphomas, a small interfering RNA (siRNA) approach was used to inhibit Syk expression. Syk siRNA effectively silenced Syk expression in both SU-DHL-1 and SR-786 cells (Figure 2a). As Syk inhibition blocks proliferation and induces apoptosis in B-cell lymphomas,1 we determined the effects of Syk siRNA on PTCL cells. In both SU-DHL-1 and SR-786, Syk siRNA significantly reduced both proliferation (3H-TdR incorporation, Figure 2b) and cell viability (annexin V assay, Figure 2c). Syk siRNA also silenced Syk expression in SeAx cells, in which Syk is not phosphorylated (data not shown). Proliferation of SeAx cells was determined after treatment with either a control or Syk siRNA in a manner identical to that described in Figure 2b. No significant difference in proliferation (67 691+/− 1974 cpm versus 73 884+/− 3467 cpm, respectively; n=3) was observed between the two treatment groups. As siRNA-based inhibition of therapeutic targets is difficult to achieve clinically, we determined whether a Syk inhibitor currently in clinical trial, R406,2 would recapitulate the functional effects of Syk siRNA in PTCL cells. As expected, R406 led to dephosphorylation of Syk in both SU-DHL-1 and SR-786 (Figure 2d). Furthermore, R406 significantly inhibited cell proliferation in a dose-dependent manner (Figure 2e), and induced cell death in both lines (Figure 2f). The approximately 30% reduction in cell viability observed was comparable to that observed (range 20–70%) in the diffuse large B-cell lymphoma lines tested (for example, DHL6, Ly3). These effects were not because of inhibition of the Syk homolog, Zap-70, as SU-DHL-1 lacks Zap-70 expression (data not shown). R406 treatment of NPM-ALK+ (and Syk−) Karpas 299 cells failed to inhibit phosphorylation of AKT and ERK 1/2 or inhibit the expression of CD274, all of which are downstream of NPM-ALK (data not shown). In addition, R406 failed to downregulate CD274 in SR-786 or SU-DHL-1 cells. Therefore, the effects observed with R406 treatment are unlikely because of the inhibition of NPM-ALK. The events leading to Syk activity in PTCLs are not understood. Syk can be phosphorylated through various receptors, including the β- and γ-chains of the interleukin-2 receptor and T-cell antigen receptor.4 Cytokines that signal through receptors sharing the γ-chain (for example, interleukin-2) may contribute to PTCL growth, but the extent to which such signaling is Syk-dependent is unclear. Both SU-DHL-1 and SR-786 are cell lines derived from anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphomas (ALCLs). The specific effects of ALK on Syk expression and activation are unknown, but warrant further study as SYK upregulation has been reported in ALK-positive ALCLs.5 Conversely, the extent to which Syk may contribute to lymphomagenesis in ALK-negative PTCLs, including PTCL unspecified, will require further study, ideally using primary tumor samples. Although ‘tonic’ B-cell receptor signaling in diffuse large B-cell lymphomas may be Syk-dependent,1 an analogous role for T-cell antigen receptor signaling in PTCLs has not been described. In fact, PTCLs often lack an intact T-cell antigen receptor-signaling apparatus, as we observed in both SU-DHL-1 and SR-786 cells (data not shown). In B-cell lymphomas, Syk phosphorylation also is regulated by protein tyrosine phosphatases (PTPs),6 and diminished PTP expression may contribute to Syk activity. As diminished PTP expression has been identified in malignant T cells, effects of PTPs on Syk regulation in PTCLs merit further study. Syk can function through a variety of downstream pathways, including MAPK, PI3K and PLC-γ activation.4 The pathways responsible for the functional effects of Syk in PTCLs are unknown. Furthermore, in addition to promoting cell growth and survival, Syk may have other functional effects in PTCLs; for example, Syk regulates tumor cell migration and cytokine production in various solid tumors.7 Finally, though normal T cells lack Syk expression, recent data indicate that Syk is overexpressed and functionally active in T cells from patients with systemic lupus erythematosis.8 Syk signaling in these cells occurs through preferential binding to Fc receptor gamma chain (FcR-γ), resulting in altered calcium flux and actin polymerization. These findings may offer additional clues to the function of Syk in PTCLs. In summary, our data provide the first evidence of a functional role for Syk in survival and growth of malignant T cells, and validate Syk as a rational therapeutic target in PTCLs. As PTCL patients currently lack good treatment options, our findings support the novel therapeutic approach of Syk inhibition for these malignancies. The authors declare no conflict of interest. This research was supported in part by the Public Health Service Grant number P50 CA097274 from the University of Iowa/Mayo Clinic Lymphoma Specialized Program of Research Excellence (UI/MC Lymphoma SPORE) and the National Cancer Institute.

Inhibition of Syk protein tyrosine kinase induces apoptosis and blocks proliferation in T-cell non-Hodgkin's lymphoma cell lines