Dimerization of MLL fusion proteins immortalizes hematopoietic cells.

MLL fusion proteins are leukemogenic, but their mechanism is unclear. Induced dimerization of a truncated MLL immortalizes bone marrow and imposes a reversible block on myeloid differentiation associated with upregulation of Hox a7, a9, and Meis1. Both dimerized MLL and exon-duplicated MLL are potent transcriptional activators, suggesting a link between dimerization and partial tandem duplication of DNA binding domains of MLL. Dimerized MLL binds with higher affinity than undimerized MLL to a CpG island within the Hox a9 locus. However, MLL-AF9 is not dimerized in vivo. The data support a model in which either MLL dimerization/exon duplication or fusion to a transcriptional activator results in Hox gene upregulation and ultimately transformation.

Molecular mechanism of tenascin-C action on matrix metalloproteinase-1 invasive potential.

The aim of the current study was to confirm that tenascin-C large splice variant (TNC320) stimulates matrix metalloproteinase-1 (MMP-1) expression and to elucidate molecular mechanisms underlying this activation. The analysis of gene expression in cultured cells grown under different conditions indicated significant increases of MMP-1 mRNA steady-state levels in the cells treated with TNC320 (200%) compared with TNC220 (100%) and bovine serum albumin (BSA), which served as controls. Gel electrophoresis results demonstrated augmented MMP-1 protein in cells cultured with TNC320, whereas slight up-regulation was noticed in cells treated with TNC220 or fibronectin. Reverse transcriptase polymerase chain reaction results demonstrated significantly higher levels of MMP-1 gene expression in TNC320 cultured cells than in all other treatment groups. The result was confirmed by examining the level of MMP-1 promoter transactivation by different extracellular proteins. Data demonstrated 30-fold activation of MMP-1 promoter by TNC320 treatment in comparison with other treatments (TNC220 or fibronectin) and BSA as a control. Both invasion and collagenase activity assays demonstrated a 3-fold difference in the cells treated with TNC320 in comparison with the control. MMP-1 was quantified by enzyme-linked immunosorbent assay as well. Experiments with constitutively active expression kinases indicated that MMP-1 expression induced by TNC320 was associated with mitogen-activated protein kinase (MAPK) cascade activation. Culture with TNC320 resulted in more than 2-fold activation of MMP1-luciferase in the presence of mitogen-activated protein kinase kinase kinase 1 and also 2-fold down-regulation in the presence of mitogen-activated protein kinase kinase 1. We hypothesize that tenascin-C stimulates invasion via up-regulation of MMP-1 expression through activation of MAPK cascade signaling.

Effect of hypothalamic proline-rich peptide (PRP-1) on neuronal and bone marrow cell apoptosis.

The AGAPEPAEPAQPGVY proline-rich peptide (PRP-1) was isolated from neurosecretory granules of the bovine neurohypophysis; it is produced by N. supraopticus and N. paraventricularis. It has been shown that PRP-1 has many potentially beneficial biological effects including immunoregulatory, hematopoietic, antimicrobial and anti-neurodegenerative properties. Here we investigated the influence of PRP-1 on staurosporine-induced apoptosis of postnatal hippocampal cells and on doxorubicin-induced bone marrow granulocyte- and monocyte apoptosis. The intention was to further characterize the effect of PRP-1 on the survival rate of neurons and in context with myelopoiesis. We demonstrate that PRP-1 significantly reduced apoptosis of postnatal hippocampal cells induced by staurosporine. The protective effect of PRP-1 against apoptotic cell death was shown to be both time- and dose-dependent. Neuroprotection was more pronounced after prolonged pretreatment of the cells with PRP-1 before the induction of apoptosis with staurosporine. The related peptide [arg(8)]vasopressin did not reveal neuroprotection. PRP-1 also significantly reduced apoptosis of bone marrow monocytes and granulocytes induced by doxorubicin. This protective effect lasted for 2-4 h and was not detectable anymore after 24 h when PRP-1 and doxorubicin were added simultaneously. Previously obtained data and results of the current studies suggested that the hypothalamic PRP-1 possibly represents an endogenous peptide whose primary functions are to regulate myelopoiesis and neuron survival as we provide evidence that PRP can differentially reduce both staurosporine- and doxorubicin-induced hippocampal and bone marrow cell apoptosis.