MEIS1 regulates an HLF-oxidative stress axis in MLL-fusion gene leukemia.

Leukemias with MLL translocations are often found in infants and are associated with poor outcomes. The pathogenesis of MLL-fusion leukemias has been linked to upregulation of HOX/MEIS1 genes. The functions of the Hox/Meis1 complex in leukemia, however, remain elusive. Here, we used inducible Meis1-knockout mice coupled with MLL-AF9 knockin mice to decipher the mechanistic role of Meis1 in established MLL leukemia. We demonstrate that Meis1 is essential for maintenance of established leukemia. In addition, in both the murine model and human leukemia cells, we found that Meis1 loss led to increased oxidative stress, oxygen flux, and apoptosis. Gene expression and chromatin immunoprecipitation studies revealed hepatic leukemia factor (HLF) as a target gene of Meis1. Hypoxia or HLF expression reversed the oxidative stress, rescuing leukemia development in Meis1-deficient cells. Thus, the leukemia-promoting properties of Meis1 are at least partly mediated by a low-oxidative state, aided by HLF. These results suggest that stimulants of oxidative metabolism could have therapeutic potential in leukemia treatment.

Meis1 preserves hematopoietic stem cells in mice by limiting oxidative stress.

The transcription factor Meis1 is expressed preferentially in hematopoietic stem cells (HSCs) and overexpressed in certain leukemias. However, the functions of Meis1 in hematopoiesis remain largely unknown. In the present study, we found that Meis1 is required for the maintenance of hematopoiesis under stress and over the long term, whereas steady-state hematopoiesis was sustained in the absence of Meis1 in inducible knock-out mice. BM cells of Meis1-deficient mice showed reduced colony formation and contained significantly fewer numbers of long-term HSCs, which exhibited loss of quiescence. Further, we found that Meis1 deletion led to the accumulation of reactive oxygen species in HSCs and decreased expression of genes implicated in hypoxia response. Finally, reactive oxygen species scavenging by N-acetyl cysteine or stabilization of hypoxia signaling by knockdown of the von-Hippel-Lindau (VHL) protein led to reversal of the effects of Meis1 deletion. The results of the present study demonstrate that Meis1 protects and preserves HSCs by restricting oxidative metabolism.

Direct inhibition of retinoblastoma phosphorylation by nimbolide causes cell-cycle arrest and suppresses glioblastoma growth.

PURPOSE: Classical pharmacology allows the use and development of conventional phytomedicine faster and more economically than conventional drugs. This approach should be tested for their efficacy in terms of complementarity and disease control. The purpose of this study was to determine the molecular mechanisms by which nimbolide, a triterpenoid found in the well-known medicinal plant Azadirachta indica, controls glioblastoma growth. EXPERIMENTAL DESIGN: Using in vitro signaling, anchorage-independent growth, kinase assays, and xenograft models, we investigated the mechanisms of its growth inhibition in glioblastoma. RESULTS: We show that nimbolide or an ethanol soluble fraction of A. indica leaves (Azt) that contains nimbolide as the principal cytotoxic agent is highly cytotoxic against glioblastoma multiforme in vitro and in vivo. Azt caused cell-cycle arrest, most prominently at the G1-S stage in glioblastoma multiforme cells expressing EGFRvIII, an oncogene present in about 20% to 25% of glioblastoma multiformes. Azt/nimbolide directly inhibited CDK4/CDK6 kinase activity leading to hypophosphorylation of the retinoblastoma protein, cell-cycle arrest at G1-S, and cell death. Independent of retinoblastoma hypophosphorylation, Azt also significantly reduced proliferative and survival advantage of glioblastoma multiforme cells in vitro and in tumor xenografts by downregulating Bcl2 and blocking growth factor-induced phosphorylation of Akt, extracellular signal-regulated kinase 1/2, and STAT3. These effects were specific because Azt did not affect mTOR or other cell-cycle regulators. In vivo, Azt completely prevented initiation and inhibited progression of glioblastoma multiforme growth. CONCLUSIONS: Our preclinical findings demonstrate nimbolide as a potent anti-glioma agent that blocks cell cycle and inhibits glioma growth in vitro and in vivo.