Enhanced inhibition of tumour growth and metastasis, and induction of antitumour immunity by IL-2-IgG2b fusion protein.

Cytokine-immunoglobulin (Ig)-fusion proteins have attracted increasing interest as antitumour agents. Here, we have investigated the antimetastatic and antitumour responses elicited in vivo by mammary adenocarcinoma cells (TS/A) engineered to secrete interleukin (IL)-2-IgG fusion proteins. TS/A cells were transfected with DNA coding for IL-2-IgG2b, IgG2b or IL-2, and injected subcutaneously into syngeneic mice. Animals injected with TS/A-IL-2 or TS/A-IL-2-IgG2b both efficiently rejected tumours, whereas treatment with parental cells or TS/A-IgG2b was lethal. Interestingly, only mice vaccinated with IL-2-IgG2b fusion protein-secreting cells showed a long-lasting protective immunity against a later challenge with parental tumour cells. Moreover, the metastatic potential of TS/A-IL-2-IgG2b-transfected cells was dramatically decreased compared with TS/A-IL-2-cells, with a virtual absence of lung metastases after intravenous injection. Adenocarcinomas secreting IL-2-IgG2b exhibited a more prominent, early and persistent infiltration of CD4+, CD8+ and natural killer (NK) cells than TS/A-IL-2 cells. Therefore, upon transfection into adenocarcinoma cells, the IgG2b part of IL-2 fusion protein exerts intriguing added antitumour properties over IL-2 alone, thus contributing to a long-lasting tumour immunity, probably by the recruitment of specific immune effector cells. These findings suggest a promising new oncotherapeutic strategy for poorly immunogenic tumours: vaccination with tumour cells engineered to secrete IL-2-IgG2b fusion protein.

The IL-15R alpha chain signals through association with Syk in human B cells.

The alpha-chain of the IL-15R (IL-15Ralpha) serves as the specific, high-affinity receptor for IL-15. It is expressed by lymphoid and nonlymphoid cells, including B cell lymphoma lines. In this study, we have further explored IL-15Ralpha-mediated signaling in activated primary B cells and in Raji cells, a human B-lymphoblastoid cell line which expresses the IL-15Ralpha and IL-2Rgamma chains, but lacks the IL-2Rbeta chain. Stimulation of Raji cells with IL-15 induces their proliferation and rescues them from C2-ceramide-induced apoptosis. By immunoprecipitation and Western blotting, we show that treatment of Raji cells and activated primary B cells with IL-15 induces coprecipitation of Syk kinase with the IL-15Ralpha chain. Upon association, the activated Syk kinase phosphorylates the IL-15Ralpha chain as well as phospholipase Cgamma, which coprecipitates with Syk. Furthermore, transfection of Raji cells with stem-loop Syk antisense oligonucleotides prevents IL-15Ralpha and phospholipase Cgamma phosphorylation as well as the inhibition of apoptosis by IL-15. Mutation of a defined region of the intracellular signaling portion of IL-15Ralpha (Tyr227) abrogates both the IL-15Ralpha/Syk association and IL-15Ralpha phosphorylation. Taken together, this suggests that Syk kinase physically and functionally associates with the IL-15Ralpha chain in B cells and that Syk plays a key role in mediating IL-15-induced signal transduction, thus accounting for the distinct functional consequences of IL-15 vs IL-2 binding to B cells.

Inhibition of keratinocyte apoptosis by IL-15: a new parameter in the pathogenesis of psoriasis?

Keratinocytes (KC) are important source of and targets for several cytokines. Although KC express IL-15 mRNA, the functional effects of IL-15 on these epithelial cells remain to be dissected. Investigating primary human foreskin KC and HaCaT cells, we show here by semiquantitative RT-PCR and flow cytometric analysis that both translate IL-15 and IL-15R mRNA and express IL-15 and IL-15Ralpha protein on the cell surface, suggesting that human KC can employ IL-15 for juxtacrine signaling. While IL-15 exerted no significant effect on KC proliferation and IL-6 or IL-8 secretion, IL-15 inhibited both anti-Fas and methylcellulose-induced KC apoptosis in vitro. This is in line with the recognized potent anti-apoptotic effects of IL-15. IL-2, whose receptor shares two components with the IL-15R, failed to inhibit KC apoptosis. Together with the role of IL-15 in sustaining chronic immune reactions, this invited the question of whether a reduction of KC apoptosis by IL-15 may be involved in the pathogenesis of psoriasis, a chronic hyperproliferative inflammatory skin disease characterized by abnormally low KC apoptosis in the epidermis. Remarkably, compared with nonlesional psoriatic skin and skin of healthy volunteers, lesional psoriatic epidermis showed high IL-15 protein expression in the epidermis and enhanced binding activity for IL-15. Therefore, antagonizing the inhibitory effects of IL-15 on KC apoptosis deserves exploration as a novel therapeutic strategy in psoriasis management.

Death deflected: IL-15 inhibits TNF-alpha-mediated apoptosis in fibroblasts by TRAF2 recruitment to the IL-15Ralpha chain.

Interleukin-15 (IL-15) is a potent inhibitor of several apoptosis pathways. One prominent path toward apoptosis is the ligand-induced association of TNF receptor 1 (TNFR1) with death domain adaptor proteins. Studying if and how IL-15 blocks TNFR1-mediated apoptosis in a murine fibroblast cell line (L929), we show here that IL-15 blocks TNFR1-induced apoptosis via IL-15Ralpha chain signaling. The intracellular tail of IL-15Ralpha shows sequence homologies to the TRAF2 binding motifs of CD30 and CD40. Most important, binding of IL-15 to IL-15Ralpha successfully competes with the TNFR1 complex for TRAF2 binding, which may impede assembly of key adaptor proteins to the TNFR1 complex, and induces IkappaBalpha phosphorylation. Thus, IL-15Ralpha chain stimulation is a powerful deflector of cell death very early in the apoptosis signaling cascade, while TNF-alpha and IL-15 surface as major opponents in apoptosis control.

[Apoptosis and thymocyte development (epithelial cells as inducers of thymocyte apoptosis)]. / Apoptoz i razvitie timotsitov (épitelial'nye kletki kak induktory apoptoza timotsitov).

Apoptosis, together with proliferation, is a main factor of selection of the clones of developing T-lymphocytes: the clones not supported by positive selection are subject to apoptosis and apoptosis accounts for discarding of potentially autoaggressive clones, i.e., for negative selection in the thymus and peripheral lymphoid tissue. Realization of apoptosis at different stages of the development of T-lymphocytes depends to a varying extent on Fas, Bcl-2, p53, and other regulators. The dendritic cells are the main cell type, the contact with determines apoptosis of T-lymphocytes. A possible role of the epithelial cells was shown in few models (on murine cells) and was not practically studied. We obtained a line of epithelial cells of the human thymus cells HTSC, cocultivation with which induces apoptosis of immature thymocytes and blood T-cells activated by mitogens. Development of apoptosis is suppressed by inhibitors of protein and RNA synthesis, chelators Ca2+, ions Zn2+, and factors destroying the cytoskeleton components. In this model, interaction of pairs of molecules CD4-HLA class II and LFA-1-ICAM-1. When in contact with the HTSC cells, the thymocytes of mice mutant for Fas-receptor (line MRL.lpr) are subject to apoptosis, but when this receptor is present, it affects the development of apoptosis.

[Protein phosphatases: structure and function]. / Proteinfosfatazy: struktura i funktsii.

The process of protein and enzyme systems phosphorylation is necessary for cell growth, differentiation and preparation for division and mitosis. The conformation changes of protein as a result of phosphorylation lead to increased enzyme activity and enhanced affinity to substrates. A large group of enzymes--protein kinases--is responsible for phosphorylation process in cell, which are divided into tyrosine- and serine-threonine-kinases depending on their ability to phosphorylate appropriate amino acid residues. In this review has been considered the functional importance and structure of protein phosphatases--enzymes, which are functional antagonists of protein kinases.

[Tyrosine protein kinase: role in the process of activating lymphocytes]. / Tirozinovye proteinkinazy: rol' v protsesse aktivatsii limfotsitov.

Some types of receptor and intracellular protein-tyrosine kinases are reviewed. These enzyme systems play an important role in activation of T- and B-lymphocytes and their precursors. The relationship is shown between the two main ways of lymphocyte activation: the phosphatidylinositol metabolic pathway, induced by protein kinase C, and the protein-tyrosine kinase pathway of intracellular protein and enzyme phosphorylation.