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ZFP36L1 and ZFP36L2 are RNA-binding proteins (RBPs) which interact with AU-rich elements in the 3'UTR of mRNA, leading to mRNA degradation and translational repression. Mice lacking ZFP36L1 and ZFP36L2 during thymopoiesis develop a Notch1-dependent T cell acute lymphoblastic leukaemia (T-ALL). Prior to the onset of T-ALL, thymic development is perturbed with accumulation of cells which have passed through the β-selection checkpoint without first expressing T cell receptor β (TCR-β). Notch1 expression is increased in non-transformed thymocytes in the absence of ZFP36L1 and ZFP36L2. Both RBPs interact with evolutionarily conserved AU-rich elements within the 3' untranslated region of Notch1 and suppress its expression. These data establish a role for ZFP36L1 and ZFP36L2 during thymocyte development and in the prevention of malignant transformation.The development of T cells in the thymus proceeds through a series of developmental stages characterised by progressive rearrangement of the T cell receptor (TCR) genes and regulated by a series of developmental checkpoints. This ordered process is orchestrated by transcription factor networks which integrate environmental cues to initiate gene expression programs appropriate to the developmental stage of the thymocyte1 -3. However there is increasing recognition that gene expression during lymphocyte development is also subject to regulation by post-transcriptional mechanisms. These affect the half-life of mRNA though promotion or

Interleukin-10 (IL-10) is an important immunomodulatory cytokine, which has attracted much attention because of its anti-inflammatory properties. It reduces antigen presentation and inhibits T cell activation. IL-10-treated myeloid cells lose their ability to respond toward the endotoxin lipopolysaccharide (LPS) with the production of several proinflammatory mediators. Thereby, IL-10 limits excessive inflammatory reactions in response to endotoxin as it occurs in colitis or endotoxin shock. Mice can be tolerized toward endotoxin shock when pretreated with a sublethal dose of LPS. This can be mimicked in vitro as LPS desensitization, resulting in a similar LPS hyporesponsiveness as observed with IL-10 pretreatment. However, an early block in LPS signaling characterizes LPS desensitization, whereas IL-10 seems to target late events. Controversial reports have been published where IL-10 would interfere with the induction of proinflammatory mediators, and little is known about the molecular mechanisms behind the anti-inflammatory activities of IL-10. Some recent publications have tried to gain more insight into the molecular mechanism of IL-10 by gene-expression profiling and functional studies in myeloid-derived cells. These results are reviewed here and compared with the progress that has been made to understand the induction of endotoxin tolerance by LPS itself.

AIBSTRACTThe RBTN2 LIM-domain protein, originally identified as an oncogenic protein in human T-cell leukemia, is essential for erythropoiesis. A possible role for RBTN2 in transcription during erythropoiesis has been investigated. Direct interaction of the RBTN2 protein was observed in vivo and in vitro with the GATAI or -2 zinc-finger transcription factors, as well as with the basic helix-loop-helix protein TALl. By using mammalian two-hybrid analysis, complexes involving RBTN2, TAL1, and GATA1, together with E47, the basic helix-loop-helix heterodimerization partner of TAL1, could be demonstrated. Thus, a molecular link exists between three proteins crucial for erythropoiesis, and the data suggest that variations in amounts of complexes involving RBTN2, TAL1, and GATAl could be important for erythroid differentiation.

BCR-ABL is a chimeric oncogene generated by translocation of sequences from the c-abl protein-tyrosine kinase gene on chromosome 9 into the BCR gene on chromosome 22. Alternative chimeric proteins, p210BCR-ABL and p190BCR-ABL, are produced that are characteristic of chronic myelogenous leukemia and acute lymphoblastic leukemia, respectively. Their role in the etiology of human leukemia remains to be defined. Transformed murine hematopoietic cells can be used as a model of BCR-ABL function since these cells can be made growth factor independent and tumorigenic by the action of the BCR-ABL oncogene. We show that the BCR-ABL oncogenes prevent apoptotic death in these cells by inducing a Bcl-2 expression pathway. Furthermore, BCR-ABL-expressing cells revert to factor dependence and nontumorigenicity after Bcl-2 expression is suppressed. These results help to explain the ability of BCR-ABL oncogenes to synergize with c-myc in cell transformation.

Recently various genetic defects in immu-

The LIM-only protein LMO2 is expressed aberrantly in acute T-cell leukaemias as a result of the chromosomal translocations t(11;14) (p13;q11) or t(7;11) (q35;p13). In a transgenic model of tumorigenesis by Lmo2, T-cell acute leukaemias arise after an asymptomatic phase in which an accumulation of immature CD4 -CD8 -double negative thymocytes occurs. Possible molecular mechanisms underlying these effects have been investigated in T cells from Lmo2 transgenic mice. Isolation of DNA-binding sites by CASTing and band shift assays demonstrates the presence of an oligomeric complex involving Lmo2 which can bind to a bipartite DNA motif comprising two E-box sequences~10 bp apart, which is distinct from that found in erythroid cells. This complex occurs in T-cell tumours and it is restricted to the immature CD4 -CD8 -thymocyte subset in asymptomatic transgenic mice. Thus, ectopic expression of Lmo2 by transgenesis, or by chromosomal translocations in humans, may result in the aberrant protein interactions causing abnormal regulation of gene expression, resulting in a blockage of T-cell differentiation and providing precursor cells for overt tumour formation.

Interleukin‐10 (IL‐10), originally identified as an inhibitor of pro‐inflammatory cytokine production, exerts multiple immunomodulatory functions. Its ability to inhibit a Th1 response has been used in clinical trials for the treatment of inflammatory diseases including psoriasis. However, little is known about the molecular mechanisms of IL‐10 functions. We aimed at identifying possiblemediators of in vitro IL‐10 treatment in monocytes by gene chip technology using Hu95a Affymetrix mRNA arrays with 12,000 genes. To prove relevance of the identified genes for the clinicalsituation we compared these in vitro results with genes being regulated by IL‐10 in peripheral blood mononuclear cells from psoriatic patients undergoing IL‐10 therapy. A high proportion of the 1,600 genes up‐regulated and 1,300 genes down‐regulated in vitro was found to be similarly regulated in vivo. Some genes, which were previously unknown to be regulated by IL‐10, can be assigned to known IL‐10 functions like e.g. the increase of pathogen clearance. Other new potentially immunomodulating genes have been identified to be regulated by IL‐10, but their impact needs to be experimentally evaluated. We could confirm a recently reported up‐regulation of heme oxygenase‐1 (HO‐1). However, we demonstrate that the anti‐inflammatory mechanisms of IL‐10 remain functional even when HO‐1 is irreversibly inhibited.