Primary structure and high expression of human agrin in basement membranes of adult lung and kidney

Abstract

Agrin is a heparan sulfate proteoglycan involved in the development of the neuromuscular junction during embryogenesis. In addition to this well-characterized function, agrin may have additional functions in other tissues and during other stages in development. In this study we present the cDNA sequence of human agrin, and demonstrate a high agrin content in adult basement membranes. The N-terminal domain of human agrin is highly similar to that of chick agrin, suggesting a similar function in laminin binding. The presence of three SGXG sequences supports serine-linked glycosylation of the core protein, two sites being particularly favorable for heparan sulfate attachment. Comparison of levels of agrin mRNA in fetal and adult human tissues showed a remarkable upregulation in adult kidney and lung. In both tissues truncated agrin transcripts were detected, lacking the region that encodes the laminin-binding domain. The high transcription levels in lung and kidney corresponded with the accumulation of agrin in the alveolar and glomerular basement membranes, suggesting a filtration-associated function. These data provide new directions for investigating the role of agrin in its different physiological environments, including the basement membranes of the neuromuscular junction, kidney and lung.Keywords : agrin; heparan sulfate proteoglycan ; glomerular basement membrane ; alveolar basement membrane ; neuromuscular junction.Agrin is a heparan sulfate proteoglycan (HSPG) of basement · glycoprotein complex [20]. Thus, agrin may anchor the BM to the cytoskeleton and be involved in signal transduction. Furthermembranes (BM). It induces aggregation of acetylcholine receptors at the neuromuscular junction (NMJ) [1, 2]. The primary more, agrin was identified recently as a major HSPG of the glomerular BM [21]. Here it could participate in the charge-selecstructures of the protein from electric ray, rat, mouse and chick have been reported [3Ϫ6]. The agrin gene was shown to encode tive ultrafiltration process. Agrin could be involved in the storage, activation, inhibition or presentation of various growth multiple isoforms through alternative splicing at three sites, designated x, y and z. These splice variants differ greatly in func-factors, and modulate their effect in a tissue-dependent manner.The human agrin gene was mapped previously to chromotion [6Ϫ9]. During the formation of the NMJ (the contact site of a motoneuron and a skeletal muscle cell), agrin isoforms ex-some 1 [5], but the cDNA structure is unknown. To obtain cDNA clones encoding full-length agrin, we used expressed-sepressed by motoneurons induce the clustering of acetylcholine receptors within the post-synaptic membrane. Isoforms ex-quence-tag information from public databases [18,22]. Here, we report the cDNA sequence of human agrin, and provide data pressed by the muscle cell do not have a clustering activity [6, 10Ϫ12]. Agrin-related proteins are also expressed in non-neural concerning its distribution in human tissues. tissues, suggesting functions in ...

Disruption of Glomerular Basement Membrane Charge through Podocyte-Specific Mutation of Agrin Does Not Alter Glomerular Permselectivity

“…22,23,40 In contrast, N-terminal antibodies label glomerular, tubular, and vascular smooth muscle BMs uniformly. 40 The reason for this discrepancy is unknown, but it might reflect alternative splicing or processing of agrin.…”

“…21 Agrin has been identified as the predominant GBM-HSPG in all species studied, prompting speculation that it may be a critical determinant of the charge barrier. 22,23 It is characterized by an ϳ2000-residue core protein of ϳ220 kd that carries at least two GAG chains, bringing its mass to ϳ400 kd. Agrin is generally classified as an HSPG, but it can carry both heparan and chondroitin sulfate (CS) GAGs.…”

Cell Adhesion Molecules in the Kidney: From Embryo to Adult

“…Expression is lost during differentiation of the bud and is totally absent in collecting ducts. In adult tissues, dystroglycan is detected in podocytes and Bowman’s capsule and localized to BMs of glomeruli and tubules but not of collecting ducts [88, 89, 90]. …”

“…It serves an alternative ligand to laminins for the transmembrane receptor dystroglycan [84]. It is expressed both in fetal and adult kidneys in the tubular BM, but in the adult it accumulates at high levels in the glomerular BM, suggesting that it may be important in filtration [88, 89]. Homozygous mutants for agrin survive to near term and show no renal phenotype, even disruption of synaptic complexes is not complete, which may reflect redundancy in deposition of dystroglycan ligands [160].…”

Matrix proteoglycans as effector molecules for epithelial cell function

“…This heparan sulphate proteoglycan is of particular interest because of the presence of endostatin, a 22 kDa antiangiogenic peptide located in the C-terminal domain of collagen XVIII [21]. Agrin is a heparan sulphate proteoglycan found in the alveolar and capillary basement membrane, which contains nine follistatin-like domains which share similarity to Kazal-type protease inhibitors, including pancreatic trypsin inhibitor, follistatin, thrombin inhibitor and elastase inhibitor [22,23].…”