Amanda Wilson

Functional crosstalk between Bmi1 and MLL/Hoxa9 axis in establishment of normal hematopoietic and leukemic stem cells.

Bmi1 is required for efficient self-renewal of hematopoietic stem cells (HSCs) and leukemic stem cells (LSCs). In this study, we investigated whether leukemia-associated fusion proteins, which differ in their ability to activate Hox expression, could initiate leukemia in the absence of Bmi1. AML1-ETO and PLZF-RARα, which do not activate Hox, triggered senescence in Bmi1(-/-) cells. In contrast, MLL-AF9, which drives expression of Hoxa7 and Hoxa9, readily transformed Bmi1(-/-) cells. MLL-AF9 could not initiate leukemia in Bmi1(-/-)Hoxa9(-/-) mice, which have further compromised HSC functions. But either gene could restore the ability of MLL-AF9 to establish LSCs in the double null background. As reported for Bmi1, Hoxa9 regulates expression of p16(Ink4a)/p19(ARF) locus and could overcome senescence induced by AML1-ETO. Together, these results reveal an important functional interplay between MLL/Hox and Bmi1 in regulating cellular senescence for LSC development, suggesting that a synergistic targeting of both molecules is required to eradicate a broader spectrum of LSCs.

Synthetic lethal targeting of oncogenic transcription factors in acute leukemia by PARP inhibitors.

Acute myeloid leukemia (AML) is mostly driven by oncogenic transcription factors, which have been classically viewed as intractable targets using small-molecule inhibitor approaches. Here we demonstrate that AML driven by repressive transcription factors, including AML1-ETO (encoded by the fusion oncogene RUNX1-RUNX1T1) and PML-RARα fusion oncoproteins (encoded by PML-RARA) are extremely sensitive to poly (ADP-ribose) polymerase (PARP) inhibition, in part owing to their suppressed expression of key homologous recombination (HR)-associated genes and their compromised DNA-damage response (DDR). In contrast, leukemia driven by mixed-lineage leukemia (MLL, encoded by KMT2A) fusions with dominant transactivation ability is proficient in DDR and insensitive to PARP inhibition. Intriguingly, genetic or pharmacological inhibition of an MLL downstream target, HOXA9, which activates expression of various HR-associated genes, impairs DDR and sensitizes MLL leukemia to PARP inhibitors (PARPis). Conversely, HOXA9 overexpression confers PARPi resistance to AML1-ETO and PML-RARα transformed cells. Together, these studies describe a potential utility of PARPi-induced synthetic lethality for leukemia treatment and reveal a novel molecular mechanism governing PARPi sensitivity in AML.

Cardiomyocyte growth and sarcomerogenesis at the intercalated disc

Cardiomyocytes grow during heart maturation or disease-related cardiac remodeling. We present evidence that the intercalated disc (ID) is integral to both longitudinal and lateral growth: increases in width are accommodated by lateral extension of the plicate tread regions and increases in length by sarcomere insertion within the ID. At the margin between myofibril and the folded membrane of the ID lies a transitional junction through which the thin filaments from the last sarcomere run to the ID membrane and it has been suggested that this junction acts as a proto Z-disc for sarcomere addition. In support of this hypothesis, we have investigated the ultrastructure of the ID in mouse hearts from control and dilated cardiomyopathy (DCM) models, the MLP-null and a cardiac-specific β-catenin mutant, cΔex3, as well as in human left ventricle from normal and DCM samples. We find that the ID amplitude can vary tenfold from 0.2xa0μm up to a maximum of ~2xa0μm allowing gradual expansion during heart growth. At the greatest amplitude, equivalent to a sarcomere length, A-bands and thick filaments are found within the ID membrane loops together with a Z-disc, which develops at the transitional junction position. Here, also, the tops of the membrane folds, which are rich in αII spectrin, become enlarged and associated with junctional sarcoplasmic reticulum. Systematically larger ID amplitudes are found in DCM samples. Other morphological differences between mouse DCM and normal hearts suggest that sarcomere inclusion is compromised in the diseased hearts.

Mediastinal large-cell lymphoma with sclerosis (MLCLS)

In a retrospective analysis encompassing a 14 year period (1978-92), 22 patients (age range 19-71, median 30 years) were identified as having mediastinal large-cell lymphoma with sclerosis on the basis of clinical and pathological features. At presentation, 15/22 had bulky disease and 11/22 had evidence of superior vena caval obstruction. Thirteen patients had stage II disease (6,II; 7,IIE), nine presented with stage IV disease. Complete remission (CR) was achieved in only 4/22 patients with the initial adriamycin-containing regimen. Good partial remission (no clinical evidence of disease, minimal abnormalities of uncertain significance on radiological investigation) was achieved in a further seven patients and poor partial remission (a reduction in measurable disease > 50%) in four, giving an overall response rate of 15/22 (68%). One patient died within 48 h of arrival at the hospital; 16 of the 17 remaining patients in whom anything less than CR was achieved subsequently received additional, alternative treatment (one chemotherapy, six mediastinal radiotherapy, nine both treatment modalities) but in only 2/16 did this result in any further degree of response. With a median follow-up of 5 1/2 years, 10/22 patients remain well without progression between 6 months and 14 years (5/6 in whom CR was eventually achieved and 5/11 in whom only partial remission was ever documented). The seven patients in whom the initial treatment demonstrably failed have all died. These results suggest that a proportion of patients with this rare subtype of high-grade B-cell lymphoma may be cured by chemotherapy alone and that the presence of a residual mediastinal mass after treatment does not necessarily imply treatment failure. However, patients in whom the initial chemotherapy fails have a very grave prognosis.

ArnS, a kinase involved in starvation‐induced archaellum expression

Organisms have evolved motility organelles that allow them to move to favourable habitats. Cells integrate environmental stimuli into intracellular signals to motility machineries to direct this migration. Many motility organelles are complex surface appendages that have evolved a tight, hierarchical regulation of expression. In the crenearchaeon Sulfolobus acidocaldarius, biosynthesis of the archaellum is regulated by regulatory network proteins that control expression of archaellum components in a phosphorylation‐dependent manner. A major trigger for archaellum expression is nutrient starvation, but although some components are known, the regulatory cascade triggered by starvation is poorly understood. In this work, the starvation‐induced Ser/Thr protein kinase ArnS (Saci_1181) which is located proximally to the archaellum operon was identified. Deletion of arnS results in reduced motility, though the archaellum is properly assembled. Therefore, our experimental and modelling results indicate that ArnS plays an essential role in the precisely controlled expression of archaellum components during starvation‐induced motility in Sulfolobus acidocaldarius. Furthermore they combined in vivo experiments and mathematical models to describe for the first time in archaea the dynamics of key regulators of archaellum expression.

Expanding the archaellum regulatory network – the eukaryotic protein kinases ArnC and ArnD influence motility of Sulfolobus acidocaldarius

Expression of the archaellum, the archaeal‐type IV pilus‐like rotating motility structure is upregulated under nutrient limitation. This is controlled by a network of regulators, called the archaellum regulatory network (arn). Several of the components of this network in Sulfolobus acidocaldarius can be phosphorylated, and the deletion of the phosphatase PP2A results in strongly increased motility during starvation, indicating a role for phosphorylation in the regulation of motility. Analysis of the motility of different protein kinase deletion strains revealed that deletion of saci_0965, saci_1181, and saci_1193 resulted in reduced motility, whereas the deletion of saci_1694 resulted in hypermotility. Here ArnC (Saci_1193) and ArnD (Saci_1694) are characterized. Purified ArnC and ArnD phosphorylate serine and threonine residues in the C‐terminus of the repressor ArnB. arnC is upregulated in starvation medium, whereas arnD is constitutively expressed. However, while differences in the expression and levels of flaB were observed in the ΔarnD strain during growth under rich conditions, under nutrient limiting conditions the ΔarnC and ΔarnD strains showed no large differences in the expression levels of the archaellum or of the studied regulators. This suggests that next to the regulation via the archaellum regulatory network additional regulatory mechanisms of expression and/or activity of the archaellum exist.

Physical Factors Affecting Outflow Facility Measurements in Mice.

PURPOSEnMice are commonly used to study conventional outflow physiology. This study examined how physical factors (hydration, temperature, and anterior chamber [AC] deepening) influence ocular perfusion measurements in mice.nnnMETHODSnOutflow facility (C) and pressure-independent outflow (Fu) were assessed by multilevel constant pressure perfusion of enucleated eyes from C57BL/6 mice. To examine the effect of hydration, seven eyes were perfused at room temperature, either immersed to the limbus in saline and covered with wet tissue paper or exposed to room air. Temperature effects were examined in 12 eyes immersed in saline at 20 °C or 35 °C. Anterior chamber deepening was examined in 10 eyes with the cannula tip placed in the anterior versus posterior chamber (PC). Posterior bowing of the iris (AC deepening) was visualized by three-dimensional histology in perfusion-fixed C57BL/6 eyes and by spectral-domain optical coherence tomography in living CD1 mice.nnnRESULTSnExposure to room air did not significantly affect C, but led to a nonzero Fu that was significantly reduced upon immersion in saline. Increasing temperature from 20 °C to 35 °C increased C by 2.5-fold, more than could be explained by viscosity changes alone (1.4-fold). Perfusion via the AC, but not the PC, led to posterior iris bowing and increased outflow.nnnCONCLUSIONSnInsufficient hydration contributes to the appearance of pressure-independent outflow in enucleated mouse eyes. Despite the large lens, AC deepening may artifactually increase outflow in mice. Temperature-dependent metabolic processes appear to influence conventional outflow regulation. Physical factors should be carefully controlled in any outflow studies involving mice.

Different clinical characteristics of paroxysmal nocturnal hemoglobinuria in pediatric and adult patients.

Studies of children with paroxysmal nocturnal hemoglobinuria (PNH) are scarce and include limited numbers of patients. We compared demographic and clinical characteristics of children and adults in the International PNH Registry. Our data show that, compared to adults with PNH, children had smaller

Sarcoplasmic reticulum is an intermediary of mitochondrial and myofibrillar growth at the intercalated disc

In cardiomyocytes columns of intermyofibrillar mitochondria run up to the intercalated disc (ID); half are collinear with those in the neighbouring cell, suggesting coordinated addition of sarcomeres and mitochondria both within and between cells during cardiomyocyte growth. Recent evidence for an association between sarcoplasmic reticulum (SR) and mitochondria indicates that the SR may be an intermediary in this coordinated behaviour. For this reason we have investigated the arrangement of SR and t tubules with respect to mitochondria and myofibrils, particularly at the ID. In the body of the cardiomyocyte the mitochondrial columns are frequently intersected by transverse tubules. In addition, we find that a majority of axial tubules are sandwiched between mitochondria and myofibril. No tubules are found at the ID. SR coats mitochondrial columns and fibrils throughout their length and reaches towards the peaks of the ID membrane where it attaches in the form of junctional (j)SR. These peripheral ID couplings are often situated between mitochondria and ID membrane, suggesting an SR connection between the two. In dilated cardiomyopathy (DCM) the mitochondria are somewhat disordered and clumped. In a mouse model for DCM, the muscle LIM protein KO, we find that there is a lack of mitochondria near the ID, suggesting the uncoupling of the myofibril/mitochondria organisation during growth. SR still coats the fibrils and reaches the ID folds in a jSR coupling. Unlike in control tissue, however, loops and long fingers of ID membrane penetrate into the proximal sarcomere suggesting a possible intermediary state in cardiomyocyte growth.

Transcriptional memory of cells of origin overrides β‐catenin requirement of MLL cancer stem cells

While β‐catenin has been demonstrated as an essential molecule and therapeutic target for various cancer stem cells (CSCs) including those driven by MLL fusions, here we show that transcriptional memory from cells of origin predicts AML patient survival and allows β‐catenin‐independent transformation in MLL‐CSCs derived from hematopoietic stem cell (HSC)‐enriched LSK population but not myeloid–granulocyte progenitors. Mechanistically, β‐catenin regulates expression of downstream targets of a key transcriptional memory gene, Hoxa9 that is highly enriched in LSK‐derived MLL‐CSCs and helps sustain leukemic self‐renewal. Suppression of Hoxa9 sensitizes LSK‐derived MLL‐CSCs to β‐catenin inhibition resulting in abolishment of CSC transcriptional program and transformation ability. In addition, further molecular and functional analyses identified Prmt1 as a key common downstream mediator for β‐catenin/Hoxa9 functions in LSK‐derived MLL‐CSCs. Together, these findings not only uncover an unexpectedly important role of cells of origin transcriptional memory in regulating CSC self‐renewal, but also reveal a novel molecular network mediated by β‐catenin/Hoxa9/Prmt1 in governing leukemic self‐renewal.