Notch signaling expands a pre-malignant pool of T-cell acute lymphoblastic leukemia clones without affecting leukemia-propagating cell frequency

NOTCH1 pathway activation contributes to the pathogenesis of over 60% of T-cell acute lymphoblastic leukemia (T-ALL). While Notch is thought to exert the majority of its effects through transcriptional activation of Myc, it also likely has independent roles in T-ALL malignancy. Here, we utilized a zebrafish transgenic model of T-ALL, where Notch does not induce Myc transcription, to identify a novel Notch gene expression signature that is also found in human T-ALL and is regulated independently of Myc. Cross-species microarray comparisons between zebrafish and mammalian disease identified a common T-ALL gene signature, suggesting that conserved genetic pathways underlie T-ALL development. Functionally, Notch expression induced a significant expansion of pre-leukemic clones; however, a majority of these clones were not fully transformed and could not induce leukemia when transplanted into recipient animals. Limiting-dilution cell transplantation revealed that Notch signaling does not increase the overall frequency of leukemia-propagating cells (LPCs), either alone or in collaboration with Myc. Taken together, these data indicate that a primary role of Notch signaling in T-ALL is to expand a population of pre-malignant thymocytes, of which a subset acquire the necessary mutations to become fully transformed LPCs

Interrogation of the RP-MDM2-P53 Axis in Human Ribosomopathies

Ribosomopathies such as Diamond-Blackfan anemia (DBA) and 5q- syndrome are human diseases characterized by heterozygous loss or mutation of ribosome-associated genes. Hallmarks of these diseases include a macrocytic anemia in an otherwise normocellular bone marrow and, in some cases, developmental defects such as craniofacial or thumb abnormalities. Haploinsufficiency of ribosome-associated genes leads to dysfunctional ribosome biogenesis, which ultimately results in inhibition of MDM2 and consequent aberrant activation of the p53 pathway. Multiple genetic models have shown that p53 loss partially or completely rescues phenotypes associated with ribosomal protein (RP) haploinsufficiency, implicating p53 as the primary driver of those phenotypes in these diseases. However, the details of the molecular cascade leading to p53 activation – the RP-MDM2-p53 axis – are not fully understood. The thesis work presented here aimed to better characterize the molecular players downstream of ribosome dysfunction involved in modulation of ribosomopathy-associated phenotypes, as well as to identify novel therapeutic opportunities. The proteomics screen characterized the protein binding partner profiles of MDM2 in cells with and without ribosome dysfunction. We found several RPs, including RPL5, RPL11, RPL23, and RPL38, to be commonly associated with MDM2, though RP deficiency may enhance the binding of RPL5 and RPL11. We also identified IGF1R as associated with MDM2 and selectively degraded in RP-deficient hematopoietic stem and progenitor cell (HSPC) cultures, and we showed that this protein loss contributes to defective erythropoiesis. In addition, a chemical screen identified calmodulin inhibitors as effective in rescuing ribosomopathy-associated phenotypes in zebrafish, mouse, and primary human HSPC models. We showed that these compounds (including the antipsychotic trifluoperazine) modulated p53 activity by inhibiting its nuclear localization, probably through inhibition of calmodulin-dependent CHK2. Lastly, we found that heterozygous RP gene deletion is a common feature of many human cancers. We further showed that silencing of a number of RPs frequently deleted in cancer results in p53 pathway activation, and that RP-deleted cancers have defects in ribosomal RNA processing. Together, this work adds novel insight to several aspects of ribosomopathy pathology and the RP-MDM2-p53 axis, and it further provides foundational evidence for novel therapeutic approaches to both ribosompathies and RP-deficient cancers.Medical Science

Bibliographies

Beichelt Timm, Bönker Frank, Kern Kristine, Hägel Peter, Raiser Simon, Kerner Ina, Pollmann Arnd, Strecke David, Walkenhaus Ralf. Bibliographies. In: Politix, vol. 15, n°59, Troisième trimestre 2002. Sciences politiques allemandes, sous la direction de Fabien Jobard et Pascale Laborier. pp. 113-146

Deletion of ribosomal protein genes is a common vulnerability in human cancer, especially in concert with TP53 mutations

Abstract Heterozygous inactivating mutations in ribosomal protein genes (RPGs) are associated with hematopoietic and developmental abnormalities, activation of p53, and altered risk of cancer in humans and model organisms. Here we performed a large‐scale analysis of cancer genome data to examine the frequency and selective pressure of RPG lesions across human cancers. We found that hemizygous RPG deletions are common, occurring in about 43% of 10,744 cancer specimens and cell lines. Consistent with p53‐dependent negative selection, such lesions are underrepresented in TP53‐intact tumors (P ≪ 10−10), and shRNA‐mediated knockdown of RPGs activated p53 in TP53‐wild‐type cells. In contrast, we did not see negative selection of RPG deletions in TP53‐mutant tumors. RPGs are conserved with respect to homozygous deletions, and shRNA screening data from 174 cell lines demonstrate that further suppression of hemizygously deleted RPGs inhibits cell growth. Our results establish RPG haploinsufficiency as a strikingly common vulnerability of human cancers that associates with TP53 mutations and could be targetable therapeutically

Transmission zone plates as analyzers for efficient parallel 2D RIXS-mapping.

We have implemented and successfully tested an off-axis transmission Fresnel zone plate as spectral analyzer for resonant inelastic X-ray scattering (RIXS). The imaging capabilities of zone plates allow for advanced two-dimensional (2D) mapping applications. By varying the photon energy along a line focus on the sample, we were able to simultaneously record the emission spectra over a range of excitation energies. Moreover, by scanning a line focus across the sample in one dimension, we efficiently recorded RIXS spectra spatially resolved in 2D, increasing the throughput by two orders of magnitude. The presented scheme opens up a variety of novel measurements and efficient, ultra-fast time resolved investigations at X-ray Free-Electron Laser sources