Nonsense-mediated mRNA decay (NMD) is a eukaryotic surveillance pathway that recognizes mRNAs with premature stop codons and targets them for rapid degradation. Evidence from previous studies has converged on UPF1 as the central NMD factor. In human cells, the SMG1 kinase phosphorylates UPF1 at the N-terminal and C-terminal tails, in turn allowing the recruitment of the NMD factors SMG5, SMG6 and SMG7. To understand the molecular mechanisms, we recapitulated these steps of NMD in vitro using purified components. We find that a short C-terminal segment of phosphorylated UPF1 containing the last two Ser-Gln motifs is recognized by the heterodimer of SMG5 and SMG7 14–3–3-like proteins. In contrast, the SMG6 14–3–3-like domain is a monomer. The crystal structure indicates that the phosphoserine binding site of the SMG6 14–3–3-like domain is similar to that of SMG5 and can mediate a weak phospho-dependent interaction with UPF1. The dominant SMG6–UPF1 interaction is mediated by a low-complexity region bordering the 14–3–3-like domain of SMG6 and by the helicase domain and C-terminal tail of UPF1. This interaction is phosphorylation independent. Our study demonstrates that SMG5–SMG7 and SMG6 exhibit different and non-overlapping modes of UPF1 recognition, thus pointing at distinguished roles in integrating the complex NMD interaction network.

The formin protein formin-like 1 (FMNL1) is highly restrictedly expressed in hematopoietic lineage-derived cells and has been previously identified as a tumor-associated antigen. However, function and regulation of FMNL1 are not well defined. We have identified a novel splice variant (FMNL1␥) containing an intron retention at the C terminus affecting the diaphanous autoinhibitory domain (DAD). FMNL1␥ is specifically located at the cell membrane and cortex in diverse cell lines. Similar localization of FMNL1 was observed for a mutant lacking the DAD domain (FMNL1⌬DAD), indicating that deregulation of autoinhibition is effective in FMNL1␥. Expression of both FMNL1␥ and FMNL1⌬DAD induces polarized nonapoptotic blebbing that is dependent on N-terminal myristoylation of FMNL1 but independent of Src and ROCK activity. Thus, our results describe N-myristoylation as a regulative mechanism of FMNL1 responsible for membrane trafficking potentially involved in a diversity of polarized processes of hematopoietic lineage-derived cells.Formins represent a protein family indispensable for many fundamental actin-dependent processes, including migration, vesicle trafficking, morphogenesis, and cytokinesis (1). Because these polarized processes are also involved in inflammation, deregulated proliferation, and metastasis, formins have been suggested to represent attractive drug targets for inflammatory and malignant diseases. Formin-like 1 (FMNL1) 3 is expressed restrictedly in hematopoietic lineagederived cells and overexpressed in malignant cells of different origin. This restricted expression suggests FMNL1 to be an attractive target for novel immunotherapies in malignant and inflammatory diseases (2, 3). However, function and regulation of FMNL1 are less well characterized. Previous work has shown involvement of FMNL1 in the reorientation of the microtubuleorganizing center toward the immunological synapse and cytotoxicity of T cells (4). The murine homolog FRL, which has 85% homology to the human counterpart, has been additionally shown to be involved in cell adhesion and motility of macrophages as well as Fc␥ receptor-mediated phagocytosis (5, 6). To date, it is not clear how these different membrane-associated processes are regulated.Formins are defined by a unique and highly conserved C-terminal formin homology (FH) 2 domain that mediates the effects on actin (7-11). The FH2 domain is proceeded by a proline-rich FH1 domain that binds with low micromolar affinity to profilin (12, 13). In a conserved subfamily of formins known as diaphanous-related formins (DRFs), the FH1 and FH2 domains are flanked by an array of regulatory domains at the N terminus and by a single C-terminal diaphanous autoregulatory domain (DAD) (14). The large N-terminal regulatory region includes a binding domain for small G proteins like RhoGTPase followed by an adjacent diaphanous-inhibitory domain (DID) and a dimerization domain (13,(15)(16)(17). The DAD, which comprised only a small stretch of amino acid residues, binds to the DID. Interaction of DA...

Cell-based immunotherapy in settings of allogeneic stem cell transplantation or donor leukocyte infusion has curative potential, especially in hematologic malignancies. However, this approach is severely restricted due to graft-versus-host disease (GvHD). This limitation may be overcome if target antigens are molecularly defined and effector cells are specifically selected. We chose formin-related protein in leukocytes 1 (FMNL1) as a target antigen after intensive investigation of its expression profile at the mRNA and protein levels. Here, we confirm re- IntroductionAlthough it is controversially discussed whether adaptive immune responses in tumor-bearing hosts play a role in controlling growth and recurrence of human tumors, 1,2 T cells can be converted to highly efficient killers of tumors. Donor leukocyte infusions (DLIs) are responsible for a graft-versus-leukemia effect (GvL) after allogeneic stem-cell transplantation (SCT), representing a therapeutic option with curative potential in different diseases at advanced stages. 3 Although GvL responses have also been shown for low-grade lymphomas, improvement of long-term survival after allogeneic transplantation has not been demonstrated in these patients. [4][5][6][7][8] This can be attributed primarily to the high treatmentassociated mortality due to transfer of T cells recognizing allogeneic minor histocompatibility (MHC) antigens, thereby causing potentially life-threatening graft-versus-host disease (GvHD). For broader applicability of this therapeutic option, it is therefore essential to reduce the risk of detrimental GvHD.One approach to gain a tumor-specific effect while significantly reducing the risk of GvHD is to generate allorestricted T cells with specificity for epitopes derived from tumor-associated antigens (TAAs). 9 Such allorestricted peptide-specific T cells may display high avidity toward MHC-presented TAAs, because they have not been negatively selected in the thymus. Moreover, they can be isolated by tetramers and cloned by limiting dilution to identify the specific TCR responsible for tumor-selective killing. 10 The isolation of a TCR with defined specificity for TAAs facilitates genetic TCR transfer into T-cell lines, 11-14 allowing major expansion of tumor-specific T cells.The choice of an appropriate target antigen is of fundamental importance for the success of an antitumor immunotherapeutic approach. So far, there is no universal antigen that serves as a target antigen in a broad range of malignancies. Many tumor-specific antigens are derived from aberrant expression of cell type-specific proteins and are expressed only in a restricted number of tumor types, limiting the tumors that can be treated. However, even the presence of a suitable antigen does not guarantee effective antigen recognition, because tumor cells evade immune recognition by down-regulation of the specific target or by inhibition of MHC class I-restricted antigen presentation. Thus, the level of epitope presentation in the context of classical or nonclassical MHC...

T cells can recognize tumor cells specifically by their TCR and the transfer of TCR-engineered T cells is a promising novel tool in anticancer therapies. We isolated and characterized four allorestricted TCRs with specificity for the HER2/neu-derived peptide 369 (HER2369) demonstrating high peptide specificity. PBMCs transduced with especially one TCR, HER2-1, mediated specific tumor reactivity after TCR optimization suggesting that this TCR represents a potential candidate for targeting HER2 by TCR-transduced effector cells. Another TCR showed high-peptide specificity without tumor reactivity. However, the TCRα-chain of this TCR specifically recognized HER2369 not only in combination with the original β-chain but also with four other β-chains of the same variable family deriving from TCRs with diverse specificities. Pairing with one β-chain derived from another HER2369-specific TCR potentiated the chimeric TCRs in regard to functional avidity, CD8 independency, and tumor reactivity. Although the frequency of such TCR single chains with dominant peptide recognition is currently unknown, they may represent interesting tools for TCR optimization resulting in enhanced functionality when paired to novel partner chains. However, undirected mispairing with novel partner chains may also result in enhanced cross-reactivity and self-reactivity. These results may have an important impact on the further design of strategies for adoptive transfer using TCR-transduced T cells.

Modulation of protein kinase C (PKC) activity has been demonstrated to either prevent or enhance drug-induced apoptosis in various tissue types. We tested four novel modulators of PKC activity in comparison to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) for the capability to affect differentiation, cell cycle progression and apoptosis in the human myeloid leukemia cell lines U937 and HL-60. Farnesyl thiotriazole (FTT) and N-(n-heptyl)-5-chloro-1-naphthalenesulfonamide (SC-10) are both direct activators of PKC, whereas 6-(2-(4-[(4-fluorophe-nyl)phenylmethylene]-1-piperidinyl)ethyl)-7-methyl-5H-thiazolo[3,2-a]pyrimidin-5-one (R59022) and [3-[2-[4-(bis-(4-fluorophenyl)methylene]piperidin-1-yl)ethyl]-2,3-dihydro-2-thioxo-4(1H)-quin-azolinone (R59949) are diacyl glycerol kinase inhibitors that activate PKC by enhancing the levels of the endogenous ligand diacyl glycerol. U937 cells displayed a slight reduction in the number of cells in G(2)/M cell cycle phase after exposure to FTT, SC-10, R59022 and R59949, respectively. In contrast, HL-60 cells demonstrated a largely unaltered cell cycle distribution. Whereas TPA treatment resulted in a strong induction of p21(WAF/CIP1), c-Fos and c-Jun levels, neither one of the novel PKC activators altered expression of these proteins. Consequently, we tested the ability of the activators to cause membrane translocation of PKC. While TPA treatment resulted in translocation of the PKC isoforms alpha, delta and epsilon, SC-10 and FTT failed to induce alterations in the PKC content of the membrane and cytosolic fractions, respectively. Expression of the beta(2)-integrin CD11c that is induced during TPA-mediated differentiation remained unaltered after exposure to SC-10 and was partly reduced after treatment with FTT. To further investigate the effect of these activators upon apoptosis in leukemic cells, HL-60 and U937 cells were treated with 1-beta-D-arabinofuranosylcytosine (Ara-C) or etoposide (VP-16). Whereas TPA strongly reduced apoptosis in Ara-C- or VP-16-treated U937 cells, little if any reduction was observed after pretreatment with either FTT, SC-10, R59022 or R59949, respectively, in these cells. In contrast, TPA enhanced apoptosis in Ara-C- or VP-16-treated HL-60 cells. Interestingly, FTT and SC-10 demonstrated a protective effect in Ara-C-treated HL-60 cells. Taken together, these data suggest that the novel PKC activators FTT, SC-10, R59022 and R59949 exhibit modest biological effects upon leukemic blast cells, and are not capable of enhancing the apoptotic response of these cells to cytotoxic drugs.