Tubulin Polymerization Modulates Interleukin-2 Receptor Signal Transduction in Human T Cells

Novel colchicine derivatives enhance graft survival after transplantation via suppression of T-cell differentiation and activity

Immunosuppressants are crucial in organ transplantation but their side effects are a trade-off for long-term use. Colchicine has been shown to be effective in various diseases, albeit with many side effects. To enhance the immunosuppressive effects of colchicine, in addition to minimizing its side effects, we attempted to synthesize new colchicine derivatives (KR compounds). In rat cardiac and pancreatic islet allograft, long-term graft survival was identified in KR compound-treated groups. The use of cyclosporine A (CsA) or colchicine inhibited the CD3⁺ and CD4⁺ T-cell proliferation, whereas KR compounds inhibited the CD8⁺ T cells as well as CD4⁺ T cells. KR compounds reduced the apoptosis, interleukin-2 receptor expression, and signal transducer and activator of transcription 3 phosphorylation more than CsA. These results indicate that KR compounds have a potential therapeutic value as novel agents for prevention of graft deterioration by allograft of rejection.

Intracellular beta-tubulin/chaperonin containing TCP1-beta complex serves as a novel chemotherapeutic target against drug-resistant tumors

In the present study, treatment of HEK-293 cells with the synthetic small molecule N-iodoacetyl-tryptophan (I-Trp) at submicromolar concentrations efficiently induced cell apoptosis as judged from the accumulation of sub-G(0) cells and intracellular DNA fragmentation. Activation of all intracellular caspases, except caspase-1, was detected in I-Trp-treated cells. Proteomic analysis revealed that beta-tubulin acted as a specific intracellular target of I-Trp. Protein fingerprinting analysis indicated that the Cys(354) residue in the peptide fragment TAVCDIPPR of beta-tubulin, which is located at the binding interface with chaperonin containing TCP1-beta (CCT-beta), was alkylated by I-Trp. Moreover, site-directed mutagenesis of Cys(354) (Cys-Ala) abolished the incorporation of I-Trp into beta-tubulin, suggesting Cys(354) is indeed the targeting site of I-Trp. Immunoprecipitation showed that the beta-tubulin/CCT-beta complex was constitutively formed but disrupted after treatment with I-Trp. Overexpression of the truncated beta-tubulin (T351-S364) or treatment with I-Trp or the synthetic peptide Myr-TAVCDIPPRG caused more severe cell apoptosis in multidrug-resistant MES-SA/Dx5 cancer cells due to higher levels of CCT-beta relative to wild-type MES-SA cancer cells. Silencing the expression of CCT-beta rendered MES-SA/Dx5 cells less sensitive to I-Trp-induced apoptotic cell death. These findings suggest that the beta-tubulin/CCT-beta complex may serve as an effective chemotherapeutic target for treating clinical tubulin-binding agent-resistant or CCT-beta-overexpressing tumors.

WIP is critical for T cell responsiveness to IL-2

The Wiskott-Aldrich syndrome (WAS) interacting protein (WIP) stabilizes the WAS protein (WASP), the product of the gene mutated in WAS. WIP-deficient T cells have low WASP levels, limiting the usefulness of WIP KO mice in defining the role of WIP in T cell function. To define this role, we compared WIP/WASP double KO (DKO) mice to WASP KO mice on DO11.10 background. T cell development was normal in both strains, but peripheral T cell numbers were significantly decreased in DKO mice. WASP KO T cells proliferated and secreted IL-2 normally in response to OVA peptide (OVAp). In contrast, T cells from DKO mice proliferated poorly in response to OVAp in vitro, and cutaneous hapten hypersensitivity was deficient in these mice. DKO T cells up-regulated CD25 expression and secreted normal amounts of IL-2 after antigen stimulation, but had defective response to IL-2, evidenced by failure to further up-regulate CD25 expression, phosphorylate STAT5, and induce expression of STAT5-dependent genes. DKO, but not WASP KO, T cells had a disrupted subcortical actin cytoskeleton and impaired actin polymerization after T cell antigen receptor (TCR) ligation. These results indicate that WIP is essential for IL-2 signaling and responsiveness in T cells, possibly because of its critical role in TCR-triggered actin cytoskeletal reorganization.

The regulatory, inflammatory, and T cell programming roles of interleukin-2 (IL-2)

Signaling through IL-2 induces the activation of pathways that lead to the proliferation, survival and cytokine production of effector T cells. However, through negative feedback mechanisms, internalization of the IL-2 receptor, induction of activation-induced cell death, and the generation of regulatory T cells, IL-2 also promotes the suppression of inflammatory responses. In regulatory T cells, IL-2 signaling upregulates the expression of FoxP3. Regulatory T cell induction by TGF-beta also requires IL-2. Additionally, pro-inflammatory and pro-survival pathways involving PI3K upon IL-2 stimulation is inhibited by PTEN in regulatory T cells. Importantly, IL-2 signaling is key for the development, expansion and maintenance of regulatory T cells. However, gamma(c) cytokines can replace requirements for IL-2 in regulatory T cells, although not with the same efficacy. The dual roles of IL-2 in inflammation are demonstrated in that mice deficient in both FoxP3 and IL-2 display less severe symptoms compared to FoxP3 deficient mice. Finally, IL-2 not only plays a key role in the induction of effector T cells and regulatory T cells, it also inhibits IL-17 producing T cells. By understanding complex dynamics of IL-2 interactions in the inflammatory response, therapies may be developed or modified for regulating immune related diseases.