Mutations in ATP2A2, encoding a Ca2+ pump, cause Darier disease

Darier disease (DD) is an autosomal-dominant skin disorder characterized by loss of adhesion between epidermal cells (acantholysis) and abnormal keratinization. Recently we constructed a 2.4-Mb, P1-derived artificial chromosome contig spanning the DD candidate region on chromosome 12q23-24.1. After screening several genes that mapped to this region, we identified mutations in the ATP2A2 gene, which encodes the sarco/endoplasmic reticulum Ca2(+)-ATPase type 2 isoform (SERCA2) and is highly expressed in keratinocytes. Thirteen mutations were identified, including frameshift deletions, in-frame deletions or insertions, splice-site mutations and non-conservative missense mutations in functional domains. Our results demonstrate that mutations in ATP2A2 cause DD and disclose a role for this pump in a Ca(2+)-signalling pathway regulating cell-to-cell adhesion and differentiation of the epidermis.     

The involvement of the renin-angiotensin system in the regulation of cell proliferation in the rat endometrium

Oestrogens are known to enhance angiotensin biosynthesis by increasing the elaboration of its precursor, angiotensinogen. On the other hand, we found that inhibition of angiotensin-converting enzyme (ACE) suppressed the proliferative response of the rat anterior pituitary gland to oestrogens. To answer the question whether the angiotensin system is involved in the control of the cell proliferation of the uterine epithelium, the effects of an ACE inhibitor, enalapril maleate, and of angiotensins II and IV, alone or together with losartan, an antagonist of angiotensin receptor type 1 (AT1), on endometrial epithelial cell proliferation have been studied. The experiments were performed on ovariectomized female Wistar rats. In the first experiment the animals were injected with a single dose of oestradiol benzoate or received an injection of solvent only. Half of the oestrogen-treated rats were injected additionally with enalapril maleate (EN, twice daily). The incorporation of bromodeoxyuridine (BrDU) into endometrial cell nuclei was used as an index of cell proliferation. It was found that oestradiol alone dramatically increased the BrDU labelling index (LI) of endometrial cell nuclei, and this effect was partially blocked by the simultaneous treatment with EN. In the second experiment, the animals were injected intraperitoneally with angiotensin II (AII), angiotensin IV (AIV) or saline, alone or together with losartan. It was found that AIV induced an increase in the LI in uterine epithelium, and this effect was not blocked by the simultaneous treatment with losartan. The increase in LI in uterine epithelium was also observed in the rats treated with AII and with losartan. These findings suggest an involvement of angiotensin IV in the control of uterine epithelium cell proliferation. Received 12 October 1998; received after revision 6 January 1999; accepted 2 February 1999     

Chemotherapy and immunotherapy of malignant glioma: molecular mechanisms and clinical perspectives

Despite the considerable progress in modern tumor therapy, the prognosis for patients with glioblastoma, the most frequent malignant brain tumor, has not been substantially improved. Although cytoreductive surgery and radiotherapy are the mainstays of treatment for malignant glioma at present, novel cytotoxic drugs and immunotherapeutic approaches hold great promise as effective weapons against these malignancies. Thus, great efforts are being made to enhance antitumoral efficacy by combining various cytotoxic agents, by novel routes of drug administration, or by combining anticancer drugs and immune modulators. Immunotherapeutic approaches include cytotoxic cytokines, targeted antibodies, and vaccination strategies. However, the success of most of these experimental therapies is prevented by the marked molecular resistance of glioma cells to diverse cytotoxic agents or by glioma-associated immunosuppression. One promising experimental strategy to target glioma is the employment of death ligands such as CD95 (Fas/Apo1) ligand or Apo2 ligand (TRAIL). Specific proapoptotic approaches may overcome many of the obvious obstacles to a satisfactory management of malignant brain tumors. Received 8 March 1999; received after revision 27 May 1999; accepted 14 June 1999     

Cell surface heparan sulfate proteoglycans and lipoprotein metabolism

Cell surface heparan sulfate proteoglycans are involved in several aspects of the lipoprotein metabolism. Most of the biological activities of these proteoglycans are mediated via interactions of their heparan sulfate moieties with various protein ligands, including lipoproteins and lipases. The binding of lipoproteins to heparan sulfate is largely determined by their apoprotein composition, and apoproteins B and E display the highest affinity for heparan sulfate. Interactions of lipoproteins with heparan sulfate are important for the cellular uptake and turnover of lipoproteins, in part by enhancing the accessibility of lipoproteins to lipoprotein receptors and lipases. Apoprotein B may interact with receptors without involving heparan sulfate. Heparan sulfate has been further implicated in presentation and stabilization of lipoprotein lipase and hepatic lipase on cell surfaces and in the transport of lipoprotein lipase from extravascular cells to the luminal surface of the endothelia. In atherosclerosis, heparan sulfate is intimately involved in several events important to the pathophysiology of the disease. Heparan sulfate thus binds and regulates the activity of growth factors, cytokines, superoxide dismutase and antithrombin, which contribute to aberrant cell proliferation, migration and matrix production, scavenging of reactive oxygen radicals and thrombosis. In this review we discuss the various roles of heparan sulfate proteoglycans in vascular biology, with emphasis on interactions of heparan sulfate with lipoproteins and lipases and the molecular basis of such interactions.     

The Pendred syndrome gene encodes a chloride-iodide transport protein

Pendred syndrome is the most common form of syndromic deafness and characterized by congenital sensorineural hearing loss and goitre. This disorder was mapped to chromosome 7 and the gene causing Pendred syndrome (PDS) was subsequently identified by positional cloning. PDS encodes a putative transmembrane protein designated pendrin. Pendrin is closely related to a family of sulfate transport proteins that includes the rat sulfate-anion transporter (encoded by Sat-1; 29% amino acid sequence identity), the human diastrophic dysplasia sulfate transporter (encoded by DTD; 32%) and the human sulfate transporter 'downregulated in adenoma' (encoded by DRA; 45%). On the basis of this homology and the presence of a slightly modified sulfate-transporter signature sequence comprising its putative second transmembrane domain, pendrin has been proposed to function as a sulfate transporter. We were unable to detect evidence of sulfate transport following the expression of pendrin in Xenopus laevis oocytes by microinjection of PDS cRNA or in Sf9 cells following infection with PDS-recombinant baculovirus. The rates of transport for iodide and chloride were significantly increased following the expression of pendrin in both cell systems. Our results demonstrate that pendrin functions as a transporter of chloride and iodide, but not sulfate, and may provide insight into thyroid physiology and the pathophysiology of Pendred syndrome.     

Arachidonic acid release by ionomycin and phorbol ester is similar in C127 epithelial cells expressing wild-type or mutated (ΔF508) cystic fibrosis transmembrane conductance regulator

The Ca²⁺ ionophore ionomycin induced cytosolic [Ca²⁺]_i elevation as well as strong activation of Cl⁻ efflux in mouse mammary epithelial cell lines expressing wild-type or mutated (deletion of phenylalaline 508) cystic fibrosis transmembrane conductance regulator (CFTR) or vector. Ionomycin-induced Cl⁻ efflux was abolished by the intracellular Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, whereas both activators and inhibitors of phospholipase A₂ had no effect, indicating the involvement of Ca²⁺-dependent Cl^- channels. Stimulation of arachidonic acid release by ionomycin and phorbol ester was not significantly different between wild-type or mutated cell lines, whereas vector-transfected cells exhibited a significant higher release, which was shown to be due to larger amount of immunoreactive cytosolic phospholipase A₂. These results indicate that phospholipase A₂ activity of C127 cells was not influenced by the presence of wild-type or mutated CFTR. Received 27 April 1999; received after revision 11 June 1999; accepted 23 July 1999