Distribution patterns of the anti-angiogenic protein ADAMTS-1 during rat development.

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-1) belongs to the large ADAM family of proteins. ADAMTS-1 contains a metalloproteinase domain, a disintegrin domain and three thrombospondin-like repeats but unlike ADAMs lacks a transmembrane domain. For the elucidation of the biological functions of ADAMTS-1, we raised new antibodies against ADAMTS-1. We show an accumulation of ADAMTS-1 protein at the basal lamina of rat embryonal epithelia of intestines, nasal cavity, choroid plexus, skin and in intracellular storage vesicles of epithelial cells. ADAMTS-1 protein seems to play a role in the development of the neuronal system, adipose tissue, muscle, heart, liver and adrenal glands. At the time of birth its presence is reduced in most organs. However, in the developing bone as well as in the skin, labelling increased towards late embryonal development. Immunoblots revealed a strong presence of a 62 kDa ADAMTS-1 fragment in kidneys, adrenal glands, lungs, intestines and heart. ADAMTS-1 was also present in the corresponding adult rat organs, but in more restricted distribution patterns. It was typically found in principal cells of collecting ducts, of the renal medulla, in ependymal cells of the ventricles and in some neurons. The results were confirmed by real-time PCR. The specific distribution pattern of ADAMTS-1 in a variety of organs during embryogenesis suggests a role of the molecule in tissue remodelling, vasculogenesis and angiogenesis.

Tumor suppressor p53 inhibits transcriptional activation of invasion gene thromboxane synthase mediated by the proto-oncogenic factor ets-1.

Cancer formation and progression is a complex process determined by several mechanisms that promote cell growth, invasiveness, neo-angiogenesis, and render neoplastic cells resistant to apoptosis. The tumor suppressor p53 and the proto-oncogenic factor ets-1 are important regulators of such mechanisms. While it is well established that p53 and ets-1 influence various aspects of cell behavior by regulating the transcription of specific genes, little is known about the functional relationship between these transcription factors. We found that the gene encoding thromboxane synthase (TXSA), which we recently identified as a factor promoting invasion and resistance to apoptosis in gliomas, is a novel target gene for both p53 and ets-1. We demonstrate that p53 and ets-1 coregulate TXSA in an antagonistic and inter-related manner, with ets-1 being a potent transcriptional activator and p53 inhibiting ets-1-dependent transcription. Negative interference with ets-1 transcription requires functional p53 and is lost in mutant p53 proteins. We show that ets-1 and p53 associate physically in vitro and in vivo and that their interaction, rather than a direct binding of p53 to the TXSA promoter, is required for transcriptional repression of TXSA by wild-type p53. An important implication of our findings is that the loss of p53-mediated negative control over ets-1-dependent transcription may lead to the acquisition of an invasive phenotype in tumor cells.

The ClC-5 chloride channel knock-out mouse - an animal model for Dent's disease.

Mutations in the gene CLCN5 encoding the vesicular chloride channel ClC-5 lead to Dent's disease, an X-linked renal disorder. Dent's disease is characterised by proteinuria, hyperphosphaturia and hypercalciuria, which eventually lead to kidney stones and nephrocalcinosis. As it was unclear how mutations in a chloride channel might cause these symptoms, we and others have generated genetic mouse models to elucidate the underlying pathophysiological mechanisms. We review results obtained from these three mouse models and present new data on endosomal acidification and vitamin D metabolism in ClC-5 knock-out (KO) mice. ClC-5 is expressed in apical endosomes of proximal tubular cells where it co-localizes with endocytosed proteins and the proton ATPase. ClC-5 may provide an electric shunt for the efficient operation of the electrogenic H(+)-ATPase. We confirmed this hypothesis by showing that endosomes from CLCN5 KO mice are acidified at a significantly lower rate than wild-type endosomes. This probably results in the drastic impairment of endocytosis observed in ClC-5 KO mice. Parathyroid hormone (PTH) is filtered into the lumen of the nephron, where it is endocytosed and degraded by proximal tubular cells. The defective endocytosis in ClC-5 KO mice entails an increased luminal concentration of PTH, subsequent stimulation of apical PTH receptors which causes an increased endocytosis of the phosphate transporter NaPi and phosphaturia. We now show that it also results in up-regulation of proximal tubular alpha-hydroxylase that generates the active form of vitamin D from its precursor. We discuss how the primary defect in endocytosis leads via secondary changes in calciotropic hormones to the tertiary symptoms hyperphosphaturia, hypercalciuria and kidney stones.