The human RUNX3/AML2 gene belongs to the 'runt domain' family of transcription factors that act as gene expression regulators in major developmental pathways. Here, we describe the expression pattern of Runx3 during mouse embryogenesis compared to the expression pattern of Runx1. E10.5 and E14.5-E16.5 embryos were analyzed using both immunohistochemistry and beta-galactosidase activity of targeted Runx3 and Runx1 loci. We found that Runx3 expression overlapped with that of Runx1 in the hematopoietic system, whereas in sensory ganglia, epidermal appendages, and developing skeletal elements, their expression was confined to different compartments. These data provide new insights into the function of Runx3 and Runx1 in organogenesis and support the possibility that cross-regulation between them plays a role in embryogenesis.

The vitamin D receptor (VDR) belongs to the thyroid hormone/retinoid receptor subfamily of nuclear receptors and functions as a heterodimer with retinoid X receptor (RXR). The RXR-VDR heterodimer, in contrast to other members of the class II nuclear receptor subfamily, is nonpermissive where RXR does not bind its cognate ligand, and therefore its role in VDR-mediated transactivation by liganded RXR-VDR has not been fully characterized. Here, we show a unique facet of the intermolecular RXR-VDR interaction, in which RXR actively participates in vitamin D3-dependent gene transcription. Using helix 3 and helix 12 mutants of VDR and RXR, we provide functional evidence that liganded VDR allosterically modifies RXR from an apo (unliganded)- to a holo (liganded)-receptor conformation, in the absence of RXR ligand. As a result of the proposed allosteric modification of RXR by liganded VDR, the heterodimerized RXR shows the "phantom ligand effect" and thus acquires the capability to recruit coactivators steroid receptor coactivator 1, transcriptional intermediary factor 2, and amplified in breast cancer-1. Finally, using a biochemical approach with purified proteins, we show that RXR augments the 1,25-dihydroxyvitamin D3-dependent recruitment of transcriptional intermediary factor 2 in the context of RXR-VDR heterodimer. These results confirm and extend the previous observations suggesting that RXR is a significant contributor to VDR-mediated gene expression and provide a mechanism by which RXR acts as a major contributor to vitamin D3-dependent transcription.

The discovery of potent and selective cyanamide-based inhibitors of the cysteine protease cathepsin C is detailed. Optimization of the template with regard to plasma stability led to the identification of compound 17, a potent cathepsin C inhibitor with excellent selectivity over other cathepsins and potent in vivo activity in a cigarette smoke mouse model.

We provide evidence of a cross-talk between nuclear receptor and Ser/Thr protein phosphatases and show that vitamin D receptor (VDR) interacts with the catalytic subunit of protein phosphatases, PP1c and PP2Ac, and induces their enzymatic activity in a ligand-dependent manner. PP1c specifically interacts with VDR but not retinoic acid receptor ␣ and retinoid X receptor ␣ in yeast. Although VDR-PP1c and VDR-PP2Ac interaction is ligand-independent in vivo, 1␣,25-dihydroxy-vitamin D 3 induces VDR-associated phosphatase activity. Further, VDR modulation of PP1c/PP2Ac activity results in a rapid and specific dephosphorylation and inactivation of their substrate, p70 S6 kinase (p70 S6k ). Finally, we demonstrate that the endogenous VDR, PP1c or PP2Ac, and p70S6k are present in a ternary complex in vivo, and the interaction of p70S6k with the VDR-PP complex is modulated by the phosphorylation state of the kinase. Since p70S6k is essential for G 1 -S transition, our results provide a molecular basis of 1␣,25-dihydroxyvitamin D 3 -induced G 1 block in colon cancer cells. Vitamin D receptor (VDR),1 a sequence-specific ligand-dependent transcription factor belonging to the family of nuclear receptors, mediates biological actions of 1␣,25-dihydroxy-vitamin D 3 (1,25(OH) 2 D 3 ). VDR heterodimerizes with retinoid X receptor (RXR), and at the molecular level VDR-RXR heterodimers induce gene expression via interaction with vitamin D response elements present in the promoter regions of responsive genes (1). This mode of action is known as the "genomic action" of VDR. However 1,25-(OH) 2 D 3 also induces gene expression by a mechanism distinct from its classical mode of action. For example, 1,25-(OH) 2 D 3 -induced expression of monocytic differentiation markers CD14 and CD11b in THP-1 cells requires phosphatidylinositol 3-kinase (PI 3-kinase) via liganddependent interaction of VDR with the regulatory (p85) subunit of PI 3-kinase (2). Similarly estrogen receptor interacts with the p85 regulatory subunit of the PI 3-kinase where estrogen receptor-PI 3-kinase interaction leads to the activation of protein kinase B/AKT and endothelial nitric-oxide synthase (3). It thus appears that cross-talk between nuclear receptors and other signal transduction pathways can lead to either induction of gene expression in a nuclear receptor-responsive element-independent manner or to extranuclear/non-genomic induction of enzymatic activities that are physiologically important, for example, in explaining the vasoprotective effects of estrogen (3). Further, nuclear receptor ligands (dexamethasone, triiodothyronine, and retinoic acid) also induce a rapid dephosphorylation of c-Jun N-terminal kinase independently of their transcriptional activation (4). Therefore, nuclear receptors appear to have a functional role both outside and inside the nucleus. Ser/Thr phosphatases are implicated in the regulation of a wide variety of cellular functions, namely metabolism, transcription, translation, development, cell growth, and differentiation (5). There are ...

No abstract