Christine Borowski

Requirement for cyclin D3 in lymphocyte development and T cell leukemias.

The D-type cyclins (cyclins D1, D2, and D3) are components of the core cell cycle machinery in mammalian cells. Cyclin D3 gene is rearranged and the protein is overexpressed in several human lymphoid malignancies. In order to determine the function of cyclin D3 in development and oncogenesis, we generated and analyzed cyclin D3-deficient mice. We found that cyclin D3(-/-) animals fail to undergo normal expansion of immature T lymphocytes and show greatly reduced susceptibility to T cell malignancies triggered by specific oncogenic pathways. The requirement for cyclin D3 also operates in human malignancies, as knock-down of cyclin D3 inhibited proliferation of acute lymphoblastic leukemias deriving from immature T lymphocytes. These studies point to cyclin D3 as a potential target for therapeutic intervention in specific human malignancies.

Constitutive pre-TCR signaling promotes differentiation through Ca 2+ mobilization and activation of NF-κB and NFAT

Pre-T cell antigen receptor (pre-TCR) signaling plays a crucial role in the development of immature T cells. Although certain aspects of proximal pre-TCR signaling have been studied, the intermediate signal transducers and the distal transcription modulators have been poorly characterized. We report here a correlation between pre-TCR signaling and a biphasic rise in the cytosolic Ca2+ concentration. In addition, we show that constitutive pre-TCR signaling is associated with an increased rate of Ca2+ influx through store-operated plasma membrane Ca2+ channels. We show also that the biphasic nature of the observed pre-TCR–induced rise in cytosolic Ca2+ differentially modulates the activities of the transcription factors NF-κB and NFAT in developing T cells.

The BCL2A1 gene as a pre-T cell receptor-induced regulator of thymocyte survival

The pre–T cell receptor (TCR) is expressed early during T cell development and imposes a tight selection for differentiating T cell progenitors. Pre-TCR–expressing cells are selected to survive and differentiate further, whereas pre-TCR− cells are “negatively” selected to die. The mechanisms of pre-TCR–mediated survival are poorly understood. Here, we describe the induction of the antiapoptotic gene BCL2A1 (A1) as a potential mechanism regulating inhibition of pre–T cell death. We characterize in detail the signaling pathway involved in A1 induction and show that A1 expression can induce pre–T cell survival by inhibiting activation of caspase-3. Moreover, we show that in vitro “knockdown” of A1 expression can compromise survival even in the presence of a functional pre-TCR. Finally, we suggest that pre-TCR–induced A1 overexpression can contribute to T cell leukemia in both mice and humans.

On the brink of becoming a T cell

Recent studies provide fresh insight into the mechanisms by which precursor cells are committed to and develop within the T-lymphocyte lineage. Precursor/product studies have identified developmental stages between that of the pluripotent hematopoietic stem cell and thymocytes committed to the T lineage. Specific ligands and signaling pathways interacting with the Notch-1 receptor and its ability to influence commitment within the lymphoid lineage have been described. Although the structural features or putative ligands endowing the pre-TCR with constitutive signaling capacity remain elusive, numerous distal mediators of pre-TCR signaling have been identified. It remains for the future to determine what roles they may have in survival, proliferation, lineage commitment and allelic exclusion of TCR genes. Receptor editing and lineage commitment of alphabeta T cells still represent controversial topics that need further study.

A critical role for the cytoplasmic tail of pTα in T lymphocyte development

Signals that emanate from the pre-T cell receptor (pre-TCR) regulate multiple processes required for the development of the αβ T cell lineage. In contrast to the γδ TCR, the pre-TCR localizes cell-autonomously to membrane rafts, where it appears to signal in a constitutive and ligand-independent manner. We addressed here the role played by structural features specific to the cytoplasmic domain of the pre-TCRα chain (pTα). More specifically, we examined a COOH-terminal proline-rich sequence that might play a role in signal transduction and a juxtamembrane cysteine residue that could be a target for palmitoylation, thus allowing spontaneous raft localization. Expression of pTα mutants in transgenic mice, retrovirally transduced T cell precursors and cell lines showed that the pTα cytoplasmic tail, in particular the proline-rich domain, plays a crucial role in pre-TCR signaling and T cell development. In contrast, the pTα juxtamembrane cysteine appeared to be dispensable for pre-TCR function.

Efficiency of RNA interference in the mouse hematopoietic system varies between cell types and developmental stages

ABSTRACT RNA interference (RNAi) is a naturally occurring posttranscriptional gene-silencing mechanism that has been adapted as a genetic tool for loss-of-function studies of a variety of organisms. It is more widely applicable than classical gene targeting and allows for the simultaneous inactivation of several homologous genes with a single transgene. Recently, RNAi has been used for conditional and conventional gene inactivation in mice. Unlike gene targeting, RNAi is a dynamic process, and its efficiency may vary both between cell types and throughout development. Here we demonstrate that RNAi can be used to target three separately encoded isoforms of the bcl-2 family gene bfl-1/A1 in a conditional manner in mice. The extent of gene inactivation varies between different cell types and is least efficient in mature lymphocytes. Our data suggest that RNAi is affected by factors beyond small interfering RNA-mRNA stoichiometry.

Pre-TCRα and TCRα Are Not Interchangeable Partners of TCRβ during T Lymphocyte Development

In contrast with the αβ T cell receptor (TCR), the pre-TCR spontaneously segregates to membrane rafts from where it signals in a cell-autonomous fashion. The disparate behaviors of these two receptors may stem either from differences inherent to the distinct developmental stages during which they are expressed, or from features intrinsic and unique to the receptor components themselves. Here, we express TCRα precisely at the pre-TCR checkpoint, at levels resembling those of endogenous pre-TCRα (pTα), and in the absence of endogenous pTα. Both in isolation and more dramatically when in competition with pTα, TCRα induced defective proliferation, survival, and differentiation of αβ T lymphocyte precursors, as well as impaired commitment to the αβ T lymphocyte lineage. Substitution of TCRα transmembrane and cytoplasmic domains with those of pTα generated a hybrid molecule possessing enhanced competitive abilities. We conclude that features intrinsic to the pre-TCR, which are absent in TCRα, are essential for its unique function.

Characterization of human non-small cell lung cancer (NSCLC) cell lines for expression of MHC, co-stimulatory molecules and tumor-associated antigens

A panel of 31 long-term non-small cell lung cancer (NSCLC) cell lines was examined for the expression of protein and/or mRNA transcripts for 11 distinct immune response related molecules or tumor associated antigens (TAA). To assess whether cytokine stimulation might up-regulate expression of the genes of interest, cells were cultured in 500 U/ml of gamma-interferon (gamma-IFN) for 48-72 h prior to analysis. Major histocompatibility complex (MHC) Class I antigens were detected by indirect immunofluorescence and were constitutively expressed on all of the cell lines. The average of the mean fluorescence intensity (MFI) measured 222+/-22. gamma-IFN stimulation produced a significant increase to 482+/-36. For MHC Class II only 7/31 cell lines (23%) exhibited constitutive expression, while gamma-IFN treatment had a dramatic effect and yielded 18/31 (58%) positive cell lines. The co-stimulatory molecules CD80 and CD86 were examined by direct immunofluorescence for cell surface expression and RT-PCR amplification for mRNA. CD80 protein was not detected at all, while an insignificant percentage of cells were positive (mean 2%) for CD86 in all cell lines tested. gamma-IFN had no apparent effect on CD80 or CD86 protein expression. Constitutive CD80 or CD86 mRNA levels were observed in 45 and 61% of the NSCLC lines, respectively. These percentages increased to 77% and 90% with gamma-IFN. Cell surface phenotypic analysis for TAA revealed positive populations in 28/31 cell lines (90%) for Her-2/neu, 18/31 (58%) for CEA and 8/31 (26%) for GD-2, with gamma-IFN having no effect. After gamma-IFN stimulation, RT-PCR amplification for Mage-1, -2, -3 and WT-1 detected mRNA in 33%, 33%, 44% and 70% of the cell lines, respectively. Overall, gamma-IFN stimulation led to the up-regulation of MHC Class I molecules and class II molecules as well as CD80 and CD86 mRNA transcripts. This survey represents the first comprehensive analysis of NSCLC cell lines for a variety of molecules that could play an important role in the generation of an NSCLC anti-tumor CD8+ cytotoxic T lymphocyte (CTL) response.

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