XIAP expression is post-transcriptionally upregulated in childhood ALL and is associated with glucocorticoid response in T-cell ALL.

BACKGROUND: Resistance to glucocorticoid induced apoptosis is one of the major risk factors for relapse and poor outcome in childhood acute lymphoblastic leukemia (ALL). Overexpression of X-linked inhibitor of apoptosis protein (XIAP) has been shown to be associated with chemotherapy resistance in several malignancies. PROCEDURE: XIAP protein and mRNA expression were determined in leukemic blasts of 51 childhood ALL patients and normal bone marrow mononuclear cells. XIAP expression was correlated with glucocorticoid response and outcome. RESULTS: XIAP protein but not mRNA expression was found to be highly increased in childhood ALL compared to control bone marrow mononuclear cells (MNC) (median: 3.5 vs. 0.14 ng/10(5) MNC, P < 0.0001) indicating a post-transcriptional regulation of XIAP expression. In patients with T-cell ALL, poor prednisone response was associated with increased XIAP expression (median: 2.8 in good vs. 5.8 in poor responders; P = 0.005). Similarly, T-cell ALL patients suffering adverse events showed higher initial XIAP levels than patients in continuous complete remission (CCR) (median: 2.7 in patients in CCR vs. 5.6 in patients suffering adverse events; P = 0.007). XIAP inhibition using the low-molecular-weight SMAC mimetic LBW242 resulted in a significant increase of prednisone-induced apoptosis in vitro. CONCLUSION: In childhood ALL compared to control bone marrow, the expression of the apoptosis inhibitor XIAP is highly increased by post-transcriptional regulation. The association with poor in vivo glucocorticoid response and outcome in T-cell ALL suggests XIAP inhibition as a promising novel approach for the treatment of resistant ALL.

Combination of host susceptibility and Mycobacterium tuberculosis virulence define gene expression profile in the host.

Progression and outcome of tuberculosis is governed by extensive crosstalk between pathogen and host. Analyses of global changes in gene expression during immune response to infection with Mycobacterium tuberculosis (M.tb) can help identify molecular markers of disease state and progression. Global distribution of M.tb strains with different degrees of virulence and drug resistance, especially for the immunocompromised host, make closer analyses of host responses more pressing than ever. Here, we describe global transcriptional responses of inducible nitric oxide synthase-deficient (iNOS(-/-)) and WT mice infected with two related M.tb strains of markedly different virulence, namely the M.tb laboratory strains H37Rv and H37Ra. Both hosts exhibited highly similar resistance to infection with H37Ra. In contrast, iNOS(-/-) mice rapidly succumbed to H37Rv, whereas WT mice developed chronic course of disease. By differential analyses, virulence-specific changes in global host gene expression were analyzed to identify molecular markers characteristic for chronic versus acute infection. We identified several markers unique for different stages of disease progression and not previously associated with virulence-specific host responses in tuberculosis.

RNA Silencing in the struggle against disease.

Numerous acquired and hereditary diseases are caused by aberrant cellular or microbial gene expression. As a result of sequencing of the human genome and the genomes of various human pathogens, researchers have gained access to a large number of genes with residual functions. For functional validation of unknown genes, their functions can be specifically inhibited by antisense nucleic acids or small interfering RNAs (siRNAs) and the consequences of the functional loss, that is, the resulting phenotypes, can be analyzed. While antisense nucleic acids block the translation stoichiometrically by docking on the mRNA, siRNAs induce a highly effective cellular mechanism that causes catalytic destruction of several mRNA molecules by a single siRNA molecule. This mechanism, called RNA interference (RNAi), is only intrinsic to eukaryotic cells. Consequently, only eukaryotic target validation is pushed by RNAi whereas time-consuming conventional knockout techniques or the less efficient antisense strategies have to be applied for prokaryotic target validation. We succeeded in triggering gene silencing by siRNA in prokaryotic cells. This opens promising perspectives regarding validation of prokaryotic gene functions.

Design of siRNAs producing unstructured guide-RNAs results in improved RNA interference efficiency.

In RNA interference (RNAi), guide RNAs direct RNA-induced silencing complexes (RISC) to their mRNA targets, thus enabling the cleavage that leads to gene silencing. We describe a strong inverse correlation between the degree of guide-RNA secondary structure formation and gene silencing by small interfering (si)RNA. Unstructured guide strands mediate the strongest silencing whereas structures with base-paired ends are inactive. Thus, the availability of terminal nucleotides within guide structures determines the strength of silencing. A to G and C to U base exchanges, which involve wobble base-pairing with the target but preserve complementarity, turned inactive into active guide structures, thereby expanding the space of functional siRNAs. Previously observed base degenerations among mature micro (mi)RNAs together with the data presented here suggest a crucial role of the guide-RNA structures in miRNA action. The analysis of the effect of the secondary structures of guide-RNA sequences on RNAi efficiency provides a basis for better understanding RNA silencing pathways and improving the design of siRNAs.