Biomedical subjects

Fotini Gounari

Publications and source records attributed to Fotini Gounari.

11 recordsLinked to original sources

PubMed2006

c-Myc mediates pre-TCR-induced proliferation but not developmental progression.

Constitutive and cell-autonomous signals emanating from the pre-T-cell receptor (pre-TCR) promote proliferation, survival and differentiation of immature thymocytes. We show here that induction of pre-TCR signaling resulted in rapid elevation of c-Myc protein levels. Cre-mediated thymocyte-specific ablation of c-Myc in CD25(+)CD44(-) thymocytes reduced proliferation and cell growth at the pre-TCR checkpoint, resulting in thymic hypocellularity and a severe reduction in CD4(+)CD8(+) thymocytes. In contrast, c-Myc deficiency did not inhibit pre-TCR-mediated differentiation or survival. Myc(-/-) double-negative (DN) 3 cells progressed to the double-positive (DP) stage and up-regulated TCRalphabeta surface expression in the absence of cell proliferation, in vivo as well as in vitro. These observations indicate that distinct signals downstream of the pre-TCR are responsible for proliferation versus differentiation, and demonstrate that c-Myc is only required for pre-TCR-induced proliferation but is dispensable for developmental progression from the DN to the DP stage.

Animals↗

PubMed2006

Differential synergy of Notch and T cell receptor signaling determines alphabeta versus gammadelta lineage fate.

Thymic precursors expressing the pre-T cell receptor (TCR), the gammadeltaTCR, or the alphabetaTCR can all enter the CD4+ 8+ alphabeta lineage, albeit with different efficacy. Here it is shown that proliferation and differentiation of precursors with the different TCRs into alphabeta lineage cells require Notch signaling at the DN3 stage of thymic development. At the DN4 stage, Notch signaling still significantly contributes to the generation of alphabeta T cells. In particular, in alphabeta lineage commitment, the pre-TCR synergizes more efficiently with Notch signals than the other two TCRs, whereas gammadeltaTCR-expressing cells can survive and expand in the absence of Notch signals, even though Notch signaling enhances their proliferation. These observations suggest a new model of alphabeta versus gammadelta lineage choice in which lineage fate is determined by the extent of synergy between TCR and Notch signaling and in which the evolutionarily recent advent of the cell-autonomously signaling pre-TCR increased the efficacy of alphabeta T cell generation.

Animals↗

PubMed2005

Loss of adenomatous polyposis coli gene function disrupts thymic development.

Loss of the adenomatous polyposis coli (APC) protein is a common initiating event in colon cancer. Here we show that thymocyte-specific loss of APC deregulated beta-catenin signaling and suppressed Notch-dependent transcription. These events promoted the proliferation of cells of the double-negative 3 and 4 stages and reduced rearrangements between the variable, diversity and joining regions of the gene encoding T cell receptor (TCR) beta, encouraging developmental progression of aberrant thymocytes lacking pre-TCR and alphabeta TCR. Simultaneously, the loss of APC prolonged the mitotic metaphase-to-anaphase checkpoint and impaired chromosome segregation, blocking development beyond the double-negative 4 stage. The result was extensive thymic atrophy and increased frequencies of thymocytes with chromosomal abnormalities. Thus, loss of APC in immature thymocytes has consequences distinct from those of deregulation of beta-catenin signaling and is essential for T cell differentiation.

Adenomatous Polyposis Coli Protein↗

PubMed2004

Pre-TCRalpha and TCRalpha are not interchangeable partners of TCRbeta during T lymphocyte development.

In contrast with the alphabeta 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 TCRalpha precisely at the pre-TCR checkpoint, at levels resembling those of endogenous pre-TCRalpha (pTalpha), and in the absence of endogenous pTalpha. Both in isolation and more dramatically when in competition with pTalpha, TCRalpha induced defective proliferation, survival, and differentiation of alphabeta T lymphocyte precursors, as well as impaired commitment to the alphabeta T lymphocyte lineage. Substitution of TCRalpha transmembrane and cytoplasmic domains with those of pTalpha generated a hybrid molecule possessing enhanced competitive abilities. We conclude that features intrinsic to the pre-TCR, which are absent in TCRalpha, are essential for its unique function.

Animals↗

PubMed2003

Efficient thymic immigration of B220+ lymphoid-restricted bone marrow cells with T precursor potential.

Using a human CD25 reporter transgene controlled by regulatory sequences from the gene encoding pre-T cell receptor alpha, we identified a common lymphocyte precursor (CLP-2) population that, in contrast to the previously identified CLP-1 population, was c-Kit-B220+. In short-term culture, the CLP-2 could be derived from the CLP-1 subset, and contained cells that in clonogenic assays were assessed to be bipotent precursors of T and B cells. Intravenous injection of bone marrow cells yielded a selective accumulation of CLP-2 thymic immigrants that in thymic organ culture generated mature alphabeta T cells. Although the CLP-2 subset may represent the most differentiated population with T cell potential before commitment to the B cell lineage, other subsets of thymic immigrants capable of generating T cells may exist.

Animals↗

PubMed2003

Thymic selection revisited: how essential is it?

Intrathymic T cell development represents one of the best studied paradigms of mammalian development. Lymphoid committed precursors enter the thymus and the Notch1 receptor plays an essential role in committing them to the T cell lineages. The pre-T cell receptor (TCR), as an autonomous cell signaling receptor, commits cells to the alphabeta lineage while its rival, the gammadeltaTCR, is involved in generating the gammadelta lineage of T cells. Positive and negative selection of immature alphabetaTCR-expressing cells are essential mechanisms for generating mature T cells, committing them to the CD4 and CD8 lineages and avoiding autoimmunity. Additional lineages of alphabetaT cells, such as the natural killer T cell lineage and the CD25+ regulatory T cell lineage, are formed when the alphabetaTCR encounters specific ligands in suitable microenvironments. Thus, positive selection and receptor-instructed lineage commitment represent a hallmark of the thymus. Ectopically expressed organ-specific antigens contribute to thymic self-nonself discrimination, which represents an essential feature for the evolutionary fitness of mammalian species.

Animals↗

PubMed2002

Stabilization of beta-catenin induces lesions reminiscent of prostatic intraepithelial neoplasia, but terminal squamous transdifferentiation of other secretory epithelia.

The present study documents that stabilization of beta-catenin is sufficient to induce lesions reminiscent of prostate intraepithelial neoplasia (PIN). Such lesions were present in all compound mutant mice and all prostate acini expressing stabilized beta-catenin. High grade PIN-like lesions resembling early human prostate cancer were detected as early as 10 weeks of age. Surprisingly, stabilization of beta-catenin in other secretory epithelia including salivary, preputial, harderian, and mammary glands induced extensive squamous metaplasia and keratinization associated with terminal differentiation of the target cells, but failed to cause neoplastic transformation. Epidermal hyperplasia, hair follicle cysts, and odontomas were also observed. The prostatic lesions exhibited upregulation of c-myc, increased rate of cellular proliferation, loss of the Na-K-Cl co-transporter NKCC1, and expression of androgen receptor. Basal cell markers such as p63 and keratin 5 were not expressed by the masses of PIN-like lesions, but were present in small foci of proliferating beta-catenin expressing basal cells. Our observations indicate that beta-catenin stabilization is a crucial event for the initiation of PIN-like lesions, but induces squamous metaplasia rather than tumorigenesis in secretory epithelia other than the prostate.

Animals↗

PubMed2002

Tracing lymphopoiesis with the aid of a pTalpha-controlled reporter gene.

A transgenic reporter mouse strain, which expressed the human CD25 (hCD25) surface marker as a reporter under the control of the pre-T cell receptor alpha(pTalpha) promoter, was used to identify lymphoid precursors that expressed pTalpha intracellularly. The hCD25 reporter marked intra- and extrathymic precursors of lymphocytes but not myeloid cells. The earliest intrathymic precursors were CD4(lo)CD8(-)CD25(-)CD44(+)c-Kit(+) cells that expressed elevated levels of Notch-1 mRNA. Clonogenic assays showed that the extrathymic precursors were common lymphoid progenitors (CLPs) that included CD19(-), B220(+), Thy1(+) and CD4(+) cells. Thus, the pTalpha reporter can be used to trace lymphopoiesis between CLPs and alphabeta T cells. The slower extinction of the hCD25 reporter compared to pTalpha enabled us to define points at which pTalpha(-) lineages branched off.

Animals↗

PubMed2002

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

Signals that emanate from the pre-T cell receptor (pre-TCR) regulate multiple processes required for the development of the alphabeta T cell lineage. In contrast to the gammadelta 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-TCRalpha chain (pTalpha). 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 pTalpha mutants in transgenic mice, retrovirally transduced T cell precursors and cell lines showed that the pTalpha cytoplasmic tail, in particular the proline-rich domain, plays a crucial role in pre-TCR signaling and T cell development. In contrast, the pTalpha juxtamembrane cysteine appeared to be dispensable for pre-TCR function.

Animals↗

PubMed2002

Activation of beta -catenin signaling in differentiated mammary secretory cells induces transdifferentiation into epidermis and squamous metaplasias.

Mammary anlagen are formed in the embryo as a derivative of the epidermis, a process that is controlled by Lef-1 and therefore possibly by beta-catenin. To investigate the role of beta-catenin signaling in mammary alveolar epithelium, we have stabilized endogenous beta-catenin in differentiating alveolar epithelium through the deletion of exon 3 (amino acids 5-80) of the beta-catenin gene. This task was accomplished in mice carrying a floxed beta-catenin gene and a Cre transgene under control of the mammary-specific whey acidic protein (WAP) gene promoter or the mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Stabilized beta-catenin was obtained during the first pregnancy, and its presence resulted in the dedifferentiation of alveolar epithelium followed by a transdifferentiation into epidermal and pilar structures. Extensive squamous metaplasia, but no adenocarcinomas, developed upon beta-catenin activation during pregnancy and persisted throughout involution. These data demonstrate that the activation of beta-catenin signaling induces a program that results in loss of mammary epithelial cell differentiation and induction of epidermal structures.

Adenocarcinoma↗

PubMed2002

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.

Animals↗