The C. elegans CBFbeta homologue BRO-1 interacts with the Runx factor, RNT-1, to promote stem cell proliferation and self-renewal

In this report, we investigate the C. elegans CBFbeta homologue, BRO-1. bro-1 mutants have a similar male-specific sensory ray loss phenotype to rnt-1 (the C. elegans homologue of the mammalian CBFbeta-interacting Runx factors), caused by failed cell divisions in the seam lineages. Our studies indicate that BRO-1 and RNT-1 form a cell proliferation-promoting complex, and that BRO-1 increases both the affinity and specificity of RNT-1-DNA interactions. Overexpression of bro-1, like rnt-1, leads to an expansion of seam cell number and co-overexpression of bro-1 and rnt-1 results in massive seam cell hyperplasia. Finally, we find that BRO-1 appears to act independently of RNT-1 in certain situations. These studies provide new insights into the function and regulation of this important cancer-associated DNA-binding complex in stem cells and support the view that Runx/CBFbeta factors have oncogenic potential.     

Contribution of phospholipase D in endothelin-1-mediated extracellular signal-regulated kinase activation and proliferation in rat uterine leiomyoma cells

Endothelin (ET)-1 is a mitogenic factor in numerous cell types, including rat myometrial cells. In the present study, we investigated the potential role of ET-1 in the proliferation of tumoral uterine smooth muscle cells (ELT-3 cells). We found that ET-1 exerted a more potent mitogenic effect in ELT-3 cells than in normal myometrial cells, as indicated by the increase in [3H]thymidine incorporation, cell number, and bromodeoxyuridine incorporation. The ET-1 was more efficient than platelet-derived growth factor and epidermal growth factor to stimulate proliferation. The ET-1-mediated cell proliferation was inhibited in the presence of U0126, a specific inhibitor of (mitogen-activated protein kinase ERK kinase), indicating that extracellular signal-regulated kinase (ERK) activation is involved. Additionally, ET-1 induced the activation of phospholipase (PL) D, leading to the synthesis of phosphatidic acid (PA). The ET-1-induced activation of PLD was twofold higher in ELT-3 cells compared to that in normal cells. The two cell types expressed mRNA for PLD1a and PLD2, whereas PLD1b was expressed only in ELT-3 cells. The exposure of cells to butan-1-ol reduced ET-1-mediated production of PA by PLD and partially inhibited ERK activation and DNA synthesis. Addition of exogenous PLD or PA in the medium reproduced the effect of ET-1 on ERK activation and cell proliferation. Collectively, these data indicate that ET-1 is a potent mitogenic factor in ELT-3 cells via a signaling pathway involving a PLD-dependent activation of ERK. This highlights the potential role of ET-1 in the development of uterine leiomyoma, and it reinforces the role of PLD in tumor growth.     

Transcriptional control and patterning of the pho-1 gene, an essential acid phosphatase expressed in the C. elegans intestine

We have previously described an acid phosphatase enzyme, PHO-1, present at the lumenal surface of all but the anterior six cells of the Caenorhabditis elegans intestine. In the present paper, we identify the pho-1 structural gene, which encodes a histidine acid phosphatase showing highest similarity to human prostatic acid phosphatase. The pho-1 5'-flanking DNA is capable of directing reporter gene expression that is both gut specific, correctly timed and correctly "patterned", that is, not expressed in the gut anterior. Furthermore, this anterior-posterior patterning of pho-1 expression responds to the C. elegans Wnt pathway as if pho-1 is repressed (directly or indirectly) by high levels of the HMG effector protein POP-1. Transgenic analysis of the pho-1 promoter shows that gut expression is critically dependent on a single WGATAR site. The gut-specific GATA factor ELT-2 binds to this site in vitro and removal of ELT-2 from the embryo destroys expression of the pho-1 reporter. Thus, all our results indicate that pho-1 is a direct downstream target of ELT-2. Finally, the pho-1 loss-of-function mutation shows an interesting and unexpected phenotype for a somatically-expressed hydrolytic enzyme: loss of pho-1 causes arrest of the majority of embryos but this lethality is a maternal effect. We suggest that pho-1 is required by the maternal intestine to assimilate some nutrient or cleavage product that is subsequently provided to the next generation of embryos.