Keeping RNA polymerase II on the run: Functions of MLL fusion partners in transcriptional regulation.

Since the identification of key MLL fusion partners as transcription elongation factors regulating expression of HOX cluster genes during hematopoiesis, extensive work from the last decade has resulted in significant progress in our overall mechanistic understanding of role of MLL fusion partner proteins in transcriptional regulation of diverse set of genes beyond just the HOX cluster. In this review, we are going to detail overall understanding of role of MLL fusion partner proteins in transcriptional regulation and thus provide mechanistic insights into possible MLL fusion protein-mediated transcriptional misregulation leading to aberrant hematopoiesis and leukemogenesis.

The cost-effectiveness of pegaspargase versus native asparaginase for first-line treatment of acute lymphoblastic leukaemia: a UK-based cost-utility analysis.

BACKGROUND: L-asparaginase is a key component of treatment for patients with acute lymphoblastic leukaemia (ALL) in the UK. Commonly used forms of asparaginase are native E. coli-derived asparaginase (native asparaginase) and pegaspargase in first-line combination therapy, and native Erwinia chrysanthemi-derived asparaginase (Erwinia asparaginase) as second-line treatment. The objective of this study was to evaluate the cost-effectiveness of pegaspargase versus native asparaginase in first-line combination therapy for patients with newly diagnosed ALL. A combined decision tree and health-state transition Markov cost-effectiveness model was developed to assess the relative costs and health outcomes of pegaspargase versus native asparaginase in the UK setting. RESULTS: In base case analyses, first-line pegaspargase (followed by Erwinia asparaginase in cases of hypersensitivity) dominated first-line native asparaginase followed by Erwinia asparaginase; i.e. resulted in lower costs and more quality-adjusted life year gain. The favourable hypersensitivity rates and administration profile of pegaspargase led to lifetime cost savings of £4741 versus native asparaginase. Pegaspargase remained cost-effective versus all treatment strategies in all scenario analyses, including use of the 2500 IU/m2 dose, recommended for patients ≤21 years of age. CONCLUSIONS: Pegaspargase, as part of multi-drug chemotherapy, is a cost-effective option for the treatment of newly diagnosed ALL. Based on this study, The National Institute for Health and Care Excellence Technology Appraisal Committee concluded that it could recommend pegaspargase as a cost-effective use of National Health Service resources in England & Wales for treating ALL in children, young people and adults with untreated, newly diagnosed disease. TRIAL REGISTRATION: UKALL 2011, EudraCT number 2010-020924-22; UKALL 2003, EudraCT number 2007-004013-34; UKALL14, EudraCT number 2009-012717-22.

Positive Regulation of Transcription by Human ZMYND8 through Its Association with P-TEFb Complex.

Although human ZMYND8 has been implicated as a transcriptional co-repressor of multiple targets, global association of ZMYND8 with active genes and enhancer regions predicts otherwise. Here, we report an additional function of ZMYND8 in transcriptional activation through its association with the P-TEFb complex. Biochemical reconstitution analyses show that human ZMYND8, through direct association with CylcinT1, forms a minimal ZMYND8-P-TEFb complex. The importance of ZMYND8 in target gene activation, through P-TEFb complex recruitment, is demonstrated on chromosomally integrated reporter gene as well as native target genes in vivo. Physiologically, we further show that the ZMYND8-P-TEFb complex-mediated transcriptional activation is required for all-trans retinoic acid (ATRA)-mediated differentiation of neuronal precursor cells. Finally, to detail the dual activator and repressor nature, mechanistically we show that, through its putative coiled-coil domain, ZMYND8 forms a homodimer that preferentially associates with the activator P-TEFb complex, whereas the monomer associates with the CHD4 subunit of repressor NuRD complex.

YAP and p73: a complex affair.

In this issue of Molecular Cell, Lapi et al. (2008) demonstrate that YAP binds p73 to activate PML transcription, which in turn mediates YAP sumoylation and stabilization, increases p73 activity, and thereby generates a DNA-damage-induced feedback loop.

Stem/progenitor cell-like properties of desmoglein 3dim cells in primary and immortalized keratinocyte lines.

We showed previously that primary keratinocytes selected for low desmoglein 3 (Dsg3) expression levels exhibited increased colony-forming efficiency and heightened proliferative potential relative to cells with higher Dsg3 expression levels, characteristics consistent with a more "stem/progenitor cell-like" phenotype. Here, we have confirmed that Dsg3(dim) cells derived from cultured primary human adult keratinocytes have comparability with alpha(6)(bri)/CD71(dim) stem cells in terms of colony-forming efficiency. Moreover, these Dsg3(dim) cells exhibit increased reconstituting ability in in vitro organotypic culture on de-epidermalized dermis (DED); they are small, actively cycling cells, and they express elevated levels of various p63 isoforms. In parallel, using the two immortalized keratinocyte cell lines HaCaT and NTERT, we obtained essentially similar though occasionally different findings. Thus, reduced colony-forming efficiency by Dsg3(bri) cells consistently was observed in both cell lines even though the cell cycle profile and levels of p63 isoforms in the bri and dim populations differed between these two cell lines. Dsg3(dim) cells from both immortalized lines produced thicker and better ordered hierarchical structural organization of reconstituted epidermis relative to Dsg3(bri) and sorted control cells. Dsg3(dim) HaCaT cells also show sebocyte-like differentiation in the basal compartment of skin reconstituted after a 4-week organotypic culture. No differences in percentages of side population cells (also a putative marker of stem cells) were detected between Dsg3(dim) and Dsg3(bri) populations. Taken together our data indicate that Dsg3(dim) populations from primary human adult keratinocytes and long-term established keratinocyte lines possess certain stem/progenitor cell-like properties, although the side population characteristic is not one of these features. Disclosure of potential conflicts of interest is found at the end of this article.

Bcr-Abl signaling through the PI-3/S6 kinase pathway inhibits nuclear translocation of the transcription factor Bach2, which represses the antiapoptotic factor heme oxygenase-1.

The malignant phenotype of chronic myeloid leukemia (CML) is due to the abnormal tyrosine kinase activity of the Bcr-Abl oncoprotein. We have previously reported that expression of the Bach2 transcription factor, which induces apoptosis in response to oxidative stress, is greatly reduced in CML cells. Because these cells are resistant to apoptosis, we tested whether Bach2 could also be regulated through posttranslational mechanisms that promote inhibition of the apoptotic response to mutagenic stimuli in CML. We found that Bach2 is phosphorylated on S521 via the phosphatidylinositol-3/S6 kinase pathway, and substitution of this site to alanine leads to nuclear accumulation of the protein, indicating that this phosphorylation is important for its subcellular localization. Ectopic expression of the S521 mutant imparts greater impairment to CML cell growth than the wild-type factor. Furthermore, we showed that Bach2 transcriptionally represses heme oxygenase-1, an antiapoptotic factor up-regulated in CML. Because CML cells are known to produce high levels of intracellular reactive oxygen species, overexpression of heme oxygenase-1 resulting from inhibition of Bach2 activity may contribute to their genomic instability and leukemic phenotype.

Akt phosphorylates the Yes-associated protein, YAP, to induce interaction with 14-3-3 and attenuation of p73-mediated apoptosis.

We have used an affinity purification method to identify substrates of protein kinase B/Akt. One protein that associates with 14-3-3 in an Akt-dependent manner is shown here to be the Yes-associated protein (YAP), which is phosphorylated by Akt at serine 127, leading to binding to 14-3-3. Akt promotes YAP localization to the cytoplasm, resulting in loss from the nucleus where it functions as a coactivator of transcription factors including p73. p73-mediated induction of Bax expression following DNA damage requires YAP function and is attenuated by Akt phosphorylation of YAP. YAP overexpression increases, while YAP depletion decreases, p73-mediated apoptosis following DNA damage, in an Akt inhibitable manner. Akt phosphorylation of YAP may thus suppress the induction of the proapoptotic gene expression response following cellular damage.