Biomedical subjects

I Screpanti

Publications and source records attributed to I Screpanti.

At least 19 recordsLinked to original sources

PubMed2006

Alternative splicing of the ErbB-4 cytoplasmic domain and its regulation by hedgehog signaling identify distinct medulloblastoma subsets.

Medulloblastoma (MB) results from aberrant development of cerebellar neurons in which altered hedgehog (Hh) signalling plays a major role. We investigated the possible influence of Hh signalling on ErbB-receptor expression in MB, in particular that of the ErbB-4 CYT-1 and CYT-2 isoforms generated by alternative splicing of the cytoplasmic domain. ErbB-4 expression was downregulated in Hh-induced MBs from Patched-1(+/-) mice. Hh signalling (reflected by enhanced expression of the Gli1 transcription factor) inhibited ErbB-4 expression in mouse cerebellar granule progenitors and human MB cells. Analysis of 26 human primary MBs revealed a subset of 11 tumors characterized by low Gli1 levels, upregulated ErbB-4 expression and increased CYT-1:CYT-2 ratios. Interestingly, CYT-1 and Gli1 levels were inversely correlated. ErbB-4 CYT-1 and CYT-2 had different phenotypic effects in cultured MB cells: in response to neuregulin treatment, CYT-2 overexpression inhibited proliferation whereas CYT-1, which includes a phosphatidylinositol 3-kinase (PI3K)-binding site that is missing in CYT-2, enhanced resistance to starvation- and etoposide-induced apoptosis by activating PI3K/Akt signalling. CYT-1:CYT-2 ratios displayed correlation with tumor histotype and ErbB-2 levels, which are established prognostic indices for MB. These findings demonstrate that low-level Hh signalling in human MB is associated with the selective maintenance of high ErbB-4 CYT-1 expression, an alteration that exerts tumor-promoting effects.

Alternative Splicing↗

PubMed2006

BRCA1 and BRCA2 genetic testing in Italian breast and/or ovarian cancer families: mutation spectrum and prevalence and analysis of mutation prediction models.

BACKGROUND: Breast cancer is an extremely complex disease, characterized by a progressive multistep process caused by interactions of both genetic and non-genetic factors. A combination of BRCA1 and BRCA2 gene mutations appears responsible for about 20%-30% of the cases with breast cancer familial history. The prevalence of BRCA1/2 pathogenic mutations largely varies within different populations; in particular, the rate of mutations in Italian breast and/or ovarian cancer families is rather controversial and ranges from 8% to 37%. PATIENTS AND METHODS: Of the 152 breast/ovarian cancer families counseled in our centre, 99 were selected for BRCA1/2 mutation screening according to our minimal criteria. The entire coding sequences and each intron/exon boundary of BRCA1/2 genes were screened by direct sequencing (PTT limited to BRCA1 exon 11). For each proband, the a priori probability of carrying a pathogenic BRCA1/2 germline mutation was calculated by means of different mutation prediction models (BRCApro, IC and Myriad Table) in order to evaluate their performances. RESULTS: Our analysis resulted in the identification of 25 and 52 variants in the BRCA1 and BRCA2 genes, respectively. Seventeen of them represent novel variants, including four deleterious truncating mutations in the BRCA2 gene (472insA, E33X, C1630X and IVS6+1G>C). Twenty-seven of the 99 probands harbored BRCA1 (n = 15) and BRCA2 (n = 12) pathogenic germline mutations, indicating an overall detection rate of 27.3% and increasing by more than 15% the spectrum of mutations in the Italian population. Furthermore, we found the lowest detection rate (19.4%) in pure hereditary breast cancer family subset. All of the prediction models showed praises and faults, with the IC software being extremely sensitive but poorly specific, compared to BRCApro. In particular all models accumulated most false-negative prediction in the HBC subset. Interestingly preliminary results of a study addressing the presence of genomic rearrangements in HBC probands with BRCApro or IC prediction scores >/=95%, provided evidence for additional mutations undetectable with our conventional screening for point mutations. CONCLUSIONS: Altogether our results suggest that HBC families, the largest pool in our series, represent an heterogeneous group where the apparently faulty performances of the prediction models might be at least partially explained by the presence of additional kinds of BRCA1/2 alteration (such as genomic rearrangements) or by mutations on different breast cancer related genes.

Adult↗

PubMed2001

EGF regulates a complex pattern of gene expression and represses smooth muscle differentiation during the neurotypic conversion of the neural-crest-derived TC-1S cell line.

EGF, known to sustain CNS neuronal progenitors, also promotes a neurotypic response in the thymic neural-crest-derived TC-1S cell line. We report here the use of TC-1S cells as a model to identify the genetic programs regulated during the neurotypic response induced by EGF and to isolate 23 EGF-responsive genes. Among them 5 represent novel cDNAs, while 18 are known genes, whose regulation by EGF is associated with the mitogenic or differentiating effects of the growth factor. The repression of smooth muscle alpha-actin and SM22alpha genes by EGF and their increase by TGFbeta suggest that the TC-1S line includes neural crest multipotent cells whose smooth muscle differentiation is repressed upon EGF treatment and stimulated by TGFbeta. Therefore, we identified a complex pattern of EGF-target genes and propose EGF as a novel signal able to recruit postmigratory neural-crest-derived cells along proliferation and cell lineage choice pathways.

Animals↗

PubMed2001

Stromal-epithelial interactions modulate estrogen responsiveness in normal human endometrium.

The coculture of endometrial epithelial cells (EEC) with stromal cells (ESC) allows achievement of an improved in vitro system for studying interactions between cells via soluble signals. The purpose of this study was to investigate whether 17beta-estradiol and insulin can induce proliferation of EEC through ESC-secreted factors. No evidence of estrogen-induced EEC proliferation has been reported so far in the conventional culture methods. To this end, we used an in vitro bicameral coculture model where human EEC were grown on extracellular matrix-coated inserts applied in dishes containing ESC. Proliferation was assessed by tritiated thymidine incorporation. Homogeneity of endometrial cell populations was ascertained immunocytochemically. 17beta-estradiol did not induce any proliferative effect on EEC cultured alone. Endometrial epithelial cell proliferation was significantly enhanced in EEC/ESC cocultures; moreover, it was further increased by 17beta-estradiol addition. Insulin increased proliferation in EEC cultured alone, but again the effect was more pronounced in EEC/ESC cocultures. Coincubation of 17beta-estradiol and an antibody against insulin-like growth factor I (IGF I) led to neutralization of ESC-mediated EEC proliferation. This work provides evidence that the effect of 17beta-estradiol on human EEC proliferation may be mediated at least in part through ESC-secreted IGF I. We also showed that insulin effect is also partially due to ESC activation.

Adult↗

PubMed2000

Expression of metabotropic glutamate receptors in murine thymocytes and thymic stromal cells.

RT-PCR combined with immunoblotting showed the expression of group-I (mGlu1 and 5) and group-II (mGlu2 and 3) metabotropic glutamate receptors in whole mouse thymus, isolated thymocytes and TC-1S thymic stromal cell line. Cytofluorimetric analysis showed that mGlu-5 receptors were absent in CD4(-)/CD8(-) but present in more mature CD4(+) CD8(+) and CD4(+)CD8(-) thymocytes. mGlu-1a receptors showed an opposite pattern of expression with respect to mGlu5, whereas mGlu2/3 receptor expression did not differ between double negative and double positive cells. mGlu receptors expressed in both thymic cell components were functional, as indicated by measurements of polyphosphoinositide hydrolysis or cAMP formation. These data suggest a possible role for mGlu receptor signalling in the thymus.

Animals↗

PubMed2000

Constitutive activation of NF-kappaB and T-cell leukemia/lymphoma in Notch3 transgenic mice.

The multiplicity of Notch receptors raises the question of the contribution of specific isoforms to T-cell development. Notch3 is expressed in CD4(-)8(-) thymocytes and is down-regulated across the CD4(-)8(-) to CD4(+)8(+) transition, controlled by pre-T-cell receptor signaling. To determine the effects of Notch3 on thymocyte development, transgenic mice were generated, expressing lck promoter-driven intracellular Notch3. Thymuses of young transgenics showed an increased number of thymocytes, particularly late CD4(-)8(-) cells, a failure to down-regulate CD25 in post-CD4(-)8(-) subsets and sustained activity of NF-kappaB. Subsequently, aggressive multicentric T-cell lymphomas developed with high penetrance. Tumors sustained characteristics of immature thymocytes, including expression of CD25, pTalpha and activated NF-kappaB via IKKalpha-dependent degradation of IkappaBalpha and enhancement of NF-kappaB-dependent anti-apoptotic and proliferative pathways. Together, these data identify activated Notch3 as a link between signals leading to NF-kappaB activation and T-cell tumorigenesis. The phenotypes of pre-malignant thymocytes and of lymphomas indicate a novel and particular role for Notch3 in co-ordinating growth and differentiation of thymocytes, across the pre-T/T cell transition, consistent with the normal expression pattern of Notch3.

Animals↗

PubMed2000

Expression of the HMGI(Y) gene products in human neuroblastic tumours correlates with differentiation status.

HMGI and HMGY are splicing variants of the HMGI(Y) gene and together with HMGI-C, belong to a family of DNA binding proteins involved in maintaining active chromatin conformation and in the regulation of gene transcription. The expression of the HMGI(Y) gene is maximal during embryonic development, declines in adult differentiated tissues and is reactivated in most transformed cells in vitro and in many human cancers in vivo. The HMGI(Y) genomic locus is frequently rearranged in mesenchymal tumours, suggesting a biological role for HMGI(Y) gene products in tumour biology. HMGIs are both target and modulators of retinoic acid activity. In fact, HMGI(Y) gene expression is differentially regulated by retinoic acid in retinoid-sensitive and -resistant neuroblastoma cells, while HMGI-C participates in conferring retinoic acid resistance in some neuroblastoma cells. In this paper we show that HMGI and HMGY isoforms are equally regulated by retinoic acid in neuroblastoma cell lines at both RNA and protein levels. More importantly our immunohistochemical analysis shows that, although HMGI(Y) is expressed in all neuroblastic tumours, consistently higher levels are observed in less differentiated neuroblastomas compared to more differentiated ganglioneuromas, indicating that HMGI(Y) expression should be evaluated as a potential diagnostic and prognostic marker in neuroblastic tumours.

Antineoplastic Agents↗

PubMed2000

The thymus at the crossroad of neuroimmune interactions.

The numerous relationships existing between the nervous and the immune systems suggest that the neural networks present in the intrathymic microenvironment may influence T-cell development. We previously reported that thymic neural-crest-derived stromal cells are involved in a neural differentiation pathway and are able to produce neurotrophic factors and neurokines that are in turn able to increase and/or modulate thymic-stromal cell neuronal phenotype. We also showed that EGF promotes a neural phenotype in thymic epithelial cells by enhancing the expression of neuronal-specific markers, neurotransmitters, and neuropoietic cytokines, such as IL-6 and CNTF. More recently we showed that the effect of EGF in directing thymic epithelial cells toward a neural-oriented cell fate is mediated by modulating the expression of genes directly involved in neurotypic differentiation (i.e., thrombospondin-1). EGF-induced regulation of stromal cells may also affect T-cell differentiation, as we observed that an EGF-pretreatment reduces the ability of thymic epithelial cells to sustain thymocyte differentiation in vitro. Finally, we demonstrated that a complex network involving the neurotrophin BDNF and its specific receptors may have a role in sustaining thymocyte precursor survival and supporting the thymocyte differentiation process. All together, our results suggest that the thymus may be the site of integration of different neuroimmune networks that are potentially involved in the regulation of thymocyte survival and/or differentiation.

Animals↗

PubMed1999

HMGI(Y) and HMGI-C genes are expressed in neuroblastoma cell lines and tumors and affect retinoic acid responsiveness.

HMGI-C and HMGI(Y) are architectural DNA-binding proteins that participate in the conformational regulation of active chromatin. Their pattern of expression in embryonal and adult tissues, the analysis of the "pygmy" phenotype induced by the inactivation of the HMGI-C gene, and their frequent qualitative or quantitative alteration in experimental and human tumors indicate their pivotal role in the control of cell growth, differentiation, and tumorigenesis in several tissues representative of the epithelial, mesenchymal, and hematopoietic lineages. In contrast, very little information is available on their expression and function in neural cells. Here, we investigated the expression of the HMGI(Y) and HMGI-C genes in neuroblastoma (NB), a tumor arising from an alteration of the normal differentiation of neural crest-derived cells and in embryonal and adult adrenal tissue. Although HMGI(Y) is constitutively expressed in the embryonal and adult adrenal gland and in all of the NB cell lines and ex vivo tumors examined, its regulation appears to be associated to growth inhibition and differentiation because we observed that HMGI(Y) expression is reduced by retinoic acid (RA) in several NB cell lines that are induced to differentiate into postmitotic neurons, whereas it is up-regulated by RA in cells that fail to differentiate. Furthermore, the decrease of HMGI(Y) expression observed in RA-induced growth arrest and differentiation is abrogated in cells that have been made insensitive to this drug by NMYC overexpression. In contrast, HMGI-C expression is down-regulated during the development of the adrenal gland, completely absent in the adult individual, and only detectable in a subset of ex vivo NB tumors and in RA-resistant NB cell lines. We provide evidence of a causal link between HMGI-C expression and resistance to the growth arrest induced by RA in NB cell lines because exogenous HMGI-C expression in HMGI-C-negative and RA-sensitive cells is sufficient to convert them into RA-resistant cells. Therefore, we suggest that HMGI-C and HMGI(Y) may participate in growth- and differentiation-related tumor progression events of neuroectodermal derivatives.

Adrenal Glands↗

PubMed1999

Thrombospondin-1 is a mediator of the neurotypic differentiation induced by EGF in thymic epithelial cells.

Thymic epithelial cell component originates from cranial neural crest as well as from endoderm and ectoderm of the third pharyngeal pouch and branchial cleft. Epidermal growth factor (EGF) has been previously shown to play a crucial role in directing thymic epithelial cells toward a neural-oriented cell fate. To identify genes that are involved in the EGF-induced neurotypic differentiation of the thymic stroma-derived TC-1S cell line, we studied EGF-treated and untreated cells by RNA fingerprinting PCR-based differential screening. We obtained 23 distinct sequences including 18 known genes and 5 sequences previously unreported, which are currently under characterization. Here, we describe the involvement of one of the isolated genes, the thrombospondin-1, as a mediator of the neurotypic differentiation induced by EGF in TC-1S cells. We show that thrombospondin-1 mRNA and protein levels are increased by EGF. Moreover, exogenous thrombospondin-1 is able to enhance the outgrowth of neurite-like processes as well as the expression of neurofilaments and neural cell adhesion molecule in TC-1S cells. These observations suggest that the up-regulation of thrombospondin-1 synthesis induced by EGF contributes to the differentiation choice of thymic epithelial cells toward a neural fate, reminiscent of their neural crest origin.

Animals↗

PubMed1999

Expression pattern of notch1, 2 and 3 and Jagged1 and 2 in lymphoid and stromal thymus components: distinct ligand-receptor interactions in intrathymic T cell development.

The suggested role of Notch1 or its mutants in thymocyte differentiation and T cell tumorigenesis raises the question of how the different members of the Notch family influence distinct steps in T cell development and the role played by Notch ligands in the thymus. We report here that different Notch receptor-ligand partnerships may occur inside the thymus, as we observed differential expression of Notch1, 2 and 3 receptors, their ligands Jagged1 and 2, and downstream intracellular effectors hairy and Enhancer of Split homolog 1 (HES-1) and hairy and Enhancer of Split homolog 5 (HES-5), depending on ontogenetic stage and thymic cell populations. Indeed, while Jagged2 is expressed in both stromal cells and thymocytes, Jagged1 expression is restricted to stromal cells. Moreover, a differential distribution of Notch3, with respect to Notch1, was observed in distinct age-related thymocyte subsets. Finally, Notch3 was preferentially up-regulated in thymocytes, following the induction of their differentiation by interaction with thymic epithelial cells expressing the cognate Jagged1 and 2 ligands, suggesting that, besides Notch1, Notch3 may also be involved in distinct steps of thymocyte development. Our results suggest that the Notch signaling pathway is involved in a complex interplay of T cell developmental stages, as a consequence of the heterogeneity and specific expression of members of the Notch receptor family and their cognate ligands, in distinct thymic cell compartments.

Animals↗

PubMed1997

2-Aminopurine unravels a role for pRB in the regulation of gene expression by transforming growth factor beta.

Transforming growth factor type beta (TGFbeta) is a pleiotropic factor that regulates different cellular activities including cell growth, differentiation, and extracellular matrix deposition. All the known effects of TGFbeta appear to be mediated by its interaction with cell surface receptors that possess a serine/threonine kinase activity. However, the intracellular signals that follow receptor activation and lead to the different cellular responses to TGFbeta are still largely unknown. On the basis of the different sensitivity to the protein kinase inhibitor 2-aminopurine and the phosphatase inhibitor okadaic acid, we identified two distinct pathways through which TGFbeta activates a genomic response. Consistently, 2-aminopurine prevented and okadaic acid potentiated the induction of JE by TGFbeta. The induction of PAI-1 and junB was instead potentiated by 2-aminopurine, after a transient inhibition and was unaffected by okadaic acid. The superinducing effect of 2-aminopurine required the presence of a functional RB protein since it was abolished in SV40 large T antigen-transfected cells, absent in the BT549 and Saos-2 RB-defective cell lines, and restored in BT549 and Saos-2 cells after reintroduction of pRB. The effects of 2-aminopurine on the TGFbeta inducible junB expression occur in all the cell lines examined suggesting that junB, and possibly other genes, can be regulated by TGFbeta through a distinct pRB-dependent pathway.

2-Aminopurine↗

PubMed1997

Interleukin-6 and CAAT/enhancer binding protein beta-deficient mice act as tools to dissect the IL-6 signalling pathway and IL-6 regulation.

Interleukin-6 (IL-6) is a pleiotropic cytokine playing important roles in immunity, hemopoiesis and inflammation. IL-6 signalling is known to involve the activation of two independent transcription factors: Stat3 (through phosphorylation by Jak kinases) and C/EBP beta (through activation of the ras pathway). In addition, C/EBP beta is believed to act as a transcriptional activator of the IL-6 gene itself. Making use of IL-6-deficient mice, we have recently demonstrated that IL-6 is essential for the induction of acute phase mRNAs in the liver upon localized tissue damage, but not upon systemically induced inflammation. Here we show that the defective mRNA induction is paralleled by a defective activation of Stat3, thus establishing a direct relationship between IL-6 function, Stat3 activation and acute phase genes induction. On the other hand, making use of C/EBP beta-deficient mice, we show that the induction of IL-6 by a variety of stimuli does not require C/EBP beta activity. In contrast to the predicted activating role of C/EBP beta, IL-6 levels are increased in the C/EBP beta-deficient mice, suggesting that C/EBP beta may act as a down-modulator of the IL-6 gene. Through the generation of C/EBP beta, IL-6 double mutant mice we show that IL-6 hyperproduction is responsible for the development of the Castleman's like lymphoproliferative disease described in the C/EBP beta-deficient mice, since the disorder is completely blocked by inactivating the IL-6 gene.

Acute-Phase Reaction↗

PubMed1997

Modulation of cytokine gene expression by thymic lympho-stromal cell to cell interaction: effect of retinoic acid.

We have examined the expression of a panel of cytokines in thymic epithelial cells and CD4-CD8- (DN) thymocytes following cell to cell lymphostromal interaction, in an experimental model which enhances in vitro thymocyte maturation. Since retinoic acid (RA) has been previously shown to be an inhibitor of thymocyte maturation process in this model, we wanted to analyse cytokine expression in DN thymocytes and thymic epithelial cells following the RA-induced impairment of in vitro thymocyte maturation. Cell to cell lymphostromal interaction results in increased IL2 and decreased IL7 expression in thymocytes while the expression of IL1 beta and IL7 increased and decreased, respectively, in thymic epithelial cells. Addition of RA to lympho-stromal cell co-culture results in the enhancement of IL4 and IL7 expression in thymocytes while in thymic epithelial cells IL1 alpha decreased and IL6 and IL7 increased. These data indicate that discrete patterns of cytokine expression are present in thymocyte precursors and in thymic epithelial cells during in vitro T-cell development. They furthermore suggest that specific cytokine modulation might contribute to the RA-induced impairment of thymocyte differentiation.

Animals↗

PubMed1996

Inactivation of the IL-6 gene prevents development of multicentric Castleman's disease in C/EBP beta-deficient mice.

Castleman's disease is a lymphoproliferative disorder thought to be related to deregulated production of IL-6. We have previously shown that mice lacking the trans-acting factor C/EBP beta, a transcriptional regulator of IL-6 and a mediator of IL-6 intracellular signaling, develop a pathology nearly identical to multicentric Castleman's disease, together with increasingly high levels of circulating IL-6. We describe here how the simultaneous inactivation of both IL-6 and C/EBP beta genes prevents the development of pathological traits of Castleman's disease observed in C/EBP beta-deficient mice. Histological and phenotypic analysis of lymph nodes and spleen of double mutant mice did not show either the lymphoadenopathy and splenomegaly or the abnormal expansion of myeloid, B and plasma cell compartments observed in C/EBP beta-/- mice, while B cell development, although delayed, was normal. Our data demonstrate that IL-6 is essential for the development of multicentric Castleman's disease in C/EBP beta-/- mice.

Animals↗

PubMed1996

Expression of trKB neurotrophin receptor during T cell development. Role of brain derived neurotrophic factor in immature thymocyte survival.

The relationships between the nervous and the immune systems raise the question of whether neurotrophic factors, in addition to the regulation of neural cell ontogeny, may influence lymphocyte development. We report in this work that the pattern of neurotrophin receptor expression depends on the developmental stage of T cells. The presence of nerve growth factor receptor trkA could not be detected in any of the thymocyte subsets, whereas brain-derived neurotrophic factor (BDNF) receptor trkB was expressed in all thymocyte subpopulations. Interestingly, both trkB mRNA and protein expression inversely correlated with the maturation stage and the differentiation potential of thymocytes, being more expressed in CD4-8- immature thymocytes and progressively declining in CD8+ and CD4+ single-positive and CD4+8+ more mature thymocytes. The developmentally regulated expression of trkB is further shown by the inhibition or enhancement of trkB expression induced by signals that either trigger or impair the transition from immature to more differentiated stages of the thymocyte developmental pathway. Signals generated following the interaction of BDNF with trkB receptor resulted in the stimulation of trkB autophosphorylation and in the up-regulation of the expression of the c-fos gene in CD4-8- cells and enhanced thymocyte survival. Finally, BDNF is expressed in thymic stroma and is further up-regulated by signals generated by the thymocyte/stromal cell interaction. These data suggest that BDNF may be a novel survival factor for thymocyte precursors and support the presence of developmentally regulated feedback mechanisms based on autocrine/paracrine neurotrophin/receptor interactions that may be involved in the thymocyte differentiation process.

Animals↗

PubMed1996

Prostaglandin E2 inhibits the interleukin-2 promoter activity through down-regulation of the Oct-dependent transcription of the octamer motif.

Prostaglandins, mainly those of the E series (PGE), are modulators of immune responses. Indeed PGE2 inhibits T cell activation and the transcription of the interleukin-2 (IL-2) gene, the major T cell growth factor. We observed that PGE2 inhibits IL-2 promoter transcription activity by interfering with signals activating the (-96 to -66 bp) octamer motif. This motif binds Oct-1 and Oct-2 as well as the phorbol ester and calcium ionophore-inducible jun and fos AP-1 factors. The PGE2-dependent down-modulation is observed in the presence of either the endogenous transacting factor Oct-1 or the exogenously expressed Oct-2. PGE2 does not regulate octamer function by influencing the jun and fos mRNA or Oct-1 protein levels or their DNA-binding abilities. Functional dissection of the octamer motif, through mutations of either the AP-1 or the octamer sites, revealed that the AP-1 site is dispensable for PGE2-dependent inhibition which instead may occur through the interference with the Oct-mediated transactivation of the octamer element. Our data suggest that the Oct-octamer interaction is a novel target of the PGE2-induced down-regulation of the IL-2 promoter.

DNA-Binding Proteins↗

PubMed1996

Human immunodeficiency virus type 1 tat protein modulates fibronectin expression in thymic epithelial cells and impairs in vitro thymocyte development.

Infection of both lymphoid and stromal components of the thymus by human immunodeficiency virus type 1 (HIV-1) suggests that impairment of lymphocyte differentiation from early T cells progenitors in the thymus may contribute to the HIV-induced T cell depletion. Cross-talk between immature thymocyte and thymic epithelium through cell-to-cell adhesion mediated by fibronectin/receptor interaction plays a central role in driving T cell development. HIV-1 tat protein, like fibronectin, contains an RGD sequence involved in the interaction with fibronectin receptor. We demonstrated that gene transfer-mediated tat expression in thymic stroma is able to influence the in vitro maturation of T cell progenitors as tat-expressing epithelial cells have a decreased ability to drive the generation of CD4+8+ thymocytes from CD4-8- precursors. Furthermore, tat-expressing cells produce more fibronectin and display upregulation of VLA-5 cell surface receptor levels compared to control cells, while alpha v expression was unchanged. Cellular distribution of fibronectin is also influenced by tat. Fibronectin is distributed in the whole cell surface and along cell processes in control cells whereas it is mainly concentrated in the intracytoplasmic area in tat-expressing cells. Therefore, expression of tat in thymic epithelial cells impairs thymocyte maturation and modulates fibronectin expression: this suggests a crucial role of this viral protein in regulating the T lymphocyte differentiation program through modulation of intrathymic lympho-stromal interactions.

Animals↗