Platelet-derived growth factor (PDGF) is a potent mitogen for cells of mesenchymal origin and is released and/or synthesized by platelets, macrophages, endothelial cells, and rat mesangial cells. In the present investigation, we found that human glomerular mesangial cells in culture release a PDGF-like protein which competes for 125I-PDGF binding to human foreskin fibroblasts and is mitogenic for these fibroblasts. The competing and to a lesser extent the mitogenic activities present in the conditioned medium are partially recognized by an anti-PDGF antibody. Northern blot analysis of poly(A)+ RNA from human mesangial cells demonstrates the expression of both PDGF A- and B-chain mRNAs. PDGF also binds to mesangial cells in a specific manner and stimulates DNA synthesis and cell proliferation. These data suggest that a PDGF-like protein secreted by mesangial cells or released from platelets, monocytes, or endothelial cells during glomerular inflammation may function as an autocrine or a paracrine growth factor for these cells. The biological role of PDGF in mediating proliferative and other inflammatory events in the glomerulus remains to be identified.

ABSTRACTcAMP regulates transcription of the gene encoding the a-subunit of human chorionic gonadotropin (hCG) in choriocarcinoma cells (BeWo). To define the sequences required for regulation by cAMP, we inserted fragments from the 5' flanking region of the a-subunit gene into a test vector containing the simian virus 40 early promoter (devoid of its enhancer) linked to the bacterial chloramphenicol acetyltransferase (CAT) gene. Results from transient expression assays in BeWo cells indicated that a 1500-base-pair (bp) fragment conferred cAMP responsiveness on the CAT gene regardless of position or orientation of the insert relative to the viral promoter. A subfragment extending from position -169 to position -100 had the same effect on cAMP-induced expression. Furthermore, the entire stimulatory effect could be achieved with an 18-bp synthetic oligodeoxynucleotide corresponding to a direct repeat between positions -146 and -111. In the absence of cAMP, the a-subunit 5' flanking sequence also enhanced transcription from the simian virus 40 early promoter. We localized this enhancer activity to the same -169/-100 fragment containing the cAMP response element.The 18-bp element alone, however, had no effect on basal expression. Thus, this short DNA sequence serves as a cAMP response element and also functions independently of other promoter-regulatory elements located in the 5' flanking sequence of the a-subunit gene.Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone expressed in the placenta. Both the a-subunit and the P-subunit are required for biological activity (1). While a physiological regulator of hCG production has not been identified, the synthesis of both subunits can be stimulated by cAMP in placental explants and in human choriocarcinoma cells (2, 3). Recent reports from several laboratories have shown that cAMP regulates expression of the chorionic gonadotropin a-and ,-subunit genes, at least in part, at the level of transcription (refs. 4 and 5; A.M., R. Cox, and J.H.N., unpublished data).In the human a-subunit gene, the first 140 base pairs (bp) of 5' flanking sequence are sufficient to confer cAMP regulation to a heterologous gene after transfection and transient expression in choriocarcinoma cells (4). This suggests that a cAMP response element lies within this region. In the present study, we have constructed several expression vectors and have used a transient expression assay to localize this element to an 18-bp sequence that is repeated between positions -146 and -111 in the 5' flanking region of the a-subunit gene. A single copy ofthis cAMP response element is sufficient to confer the same degree of cAMP regulation as a 1500-bp fragment containing the a-subunit promoter. This response element functions independently of other promoter regulatory elements. PROCEDURES Construction of Vectors. Construction of the expression vector pHaCAT (Fig. 1A) was initiated by isolating a 1500-bp DNA fragment from the genomic clone of the human asubunit gene provided by J. Fiddes (6). ...

Platelet-derived growth factor (PDGF) has been implicated in several nonmalignant pathophysiological processes, including proliferative diseases of the kidney. Glomerular mesangial cells secrete a PDGF-like factor and express the PDGF A-chain and c-sis (or B-chain) mRNAs. We report here that both mRNAs are induced by serum and this effect can be mimicked by recombinant PDGF, which also markedly stimulates DNA synthesis. Other growth factors, such as epidermal growth factor (EGF), transforming growth factor type alpha, basic fibroblast growth factor (bFGF), and tumor necrosis factor type alpha (TNF-alpha) also are mitogenic for human mesangial cells and induce expression of the PDGF mRNAs. EGF, TNF-alpha, and bFGF also stimulate these cells to secrete a PDGF-like factor. Furthermore, anti-PDGF antibody partially abrogates the mitogenic effect of EGF, suggesting that mitogen-stimulated PDGF synthesis in mesangial cells is at least partly responsible for cell growth induced by other growth factors. In contrast to these results, transforming growth factor type beta (TGF-beta), while inducing both mRNAs, is not mitogenic, indicating that its effect on message levels can be dissociated from DNA synthesis. These data suggest that several peptide growth factors regulate the growth of mesangial cells and that PDGF may be an effector molecule that plays a role in the mitogenic response to many of these growth stimuli.

Summary Deficiency of von Willebrand factor (VWF) cleaving protease ADAMTS13 has been demonstrated to be the proximate cause of a subset of thrombotic microangiopathic haemolytic anaemias (MAHA) typical for thrombotic thrombocytopenic purpura (TTP). ADAMTS13 gene mutations cause the hereditary form; acquired deficiency has been attributed to presence of an autoantibody, which may represent a specific subset of MAHA best termed ‘autoimmune thrombotic thrombocytopenic purpura’. We describe a patient with relapsing TTP because of ADAMTS13 inhibitors, who failed to achieve sustained remission despite therapies with plasma exchange, steroids, vincristine, staphylococcal protein A and splenectomy. The ADAMTS13 inhibitor titre remained elevated and clinical stability was only maintained by plasma exchange every 2–3 d over a period of 268 d. The patient then received rituximab therapy (eight doses of 375 mg/m2 weekly), during which she required five plasma exchanges in the first 10 d, two exchanges in the next 3 weeks, and none thereafter for 450 d and ongoing. The ADAMTS13 inhibitor titre decreased and enzyme activity increased. We compared this case with that of seven previously reported TTP cases also treated with rituximab; experience suggests that rituximab therapy deserves further investigation for patients with either refractory or relapsing TTP caused by ADAMTS13 inhibitors.