Molecular cloning and expression of rat betacellulin cDNA

EGFR signaling in renal fibrosis

Signaling through the epidermal growth factor receptor (EGFR) is involved in regulation of multiple biological processes, including proliferation, metabolism, differentiation, and survival. Owing to its aberrant expression in a variety of malignant tumors, EGFR has been recognized as a target in anticancer therapy. Increasingly, evidence from animal studies indicates that EGFR signaling is also implicated in the development and progression of renal fibrosis. The therapeutic value of EGFR inhibition has not yet been evaluated in human kidney disease. In this article, we summarize recent research into the role of EGFR signaling in renal fibrogenesis, discuss the mechanism by which EGFR regulates this process, and consider the potential of EGFR as an antifibrotic target.

Betacellulin overexpression in transgenic mice improves glucose tolerance and enhances insulin secretion by isolated islets in vitro

Betacellulin (BTC), a ligand of the epidermal growth factor receptor, has been shown to promote growth and differentiation of pancreatic beta-cells and to improve glucose metabolism in experimental diabetic rodent models. We employed transgenic mice (BTC-tg) to investigate the effects of long-term BTC overabundance on islet structure and glucose metabolism. Expression of BTC is increased in transgenic islets, which show normal structure and distribution of the different endocrine cell types, without pathological alterations. BTC-tg mice exhibit lower fasted glucose levels and improved glucose tolerance associated with increased glucose-induced insulin secretion. Surprisingly, quantitative stereological analyses revealed that, in spite of increased cell proliferation, the islet and beta-cell volumes were unchanged in BTC-tg mice, suggesting enhanced cell turnover. Insulin secretion in vitro was significantly higher in transgenic islets in medium containing high glucose (11.2 or 16.7mM) as compared to control islets. Our results demonstrate that long-term BTC overabundance does not alter pancreatic islet structure and beta-cell mass, but enhances glucose-induced insulin secretion in vivo as well as in vitro.

The role of the EGF family of ligands and receptors in renal development, physiology and pathophysiology

Mammalian kidney expresses all of the members of the ErbB family of receptors and their respective ligands. Studies support a role for ErbB family receptor activation in kidney development and differentiation. Under physiologic conditions, EGFR activation appears to play an important role in the regulation of renal hemodynamics and electrolyte handling by the kidney, while in different pathophysiologic states, EGFR activation may mediate either beneficial or detrimental effects to the kidney. This article provides an overview of the expression profile of the ErbB family of ligands and receptors in the mammalian kidney and summarizes known physiological and pathophysiological roles of EGFR activation in the organ.

Signal transduction of betacellulin in growth and migration of vascular smooth muscle cells

Epidermal growth factor (EGF) family ligands have been implicated in cardiovascular diseases because of their enhanced expression in vascular lesions and their promoting effects on growth and migration of vascular smooth muscle cells (VSMCs). Betacellulin (BTC), a novel EGF family ligand, has been shown to be expressed in atherosclerotic lesions and to be a potent growth factor of VSMCs. However, the molecular mechanisms downstream of BTC involved in mediating vascular remodeling remain largely unknown. Therefore, the aim of this study was to examine the effects of BTC on signal transduction, growth, and migration in VSMCs. We found that BTC stimulated phosphorylation of EGF receptor (EGFR) at Tyr1068, which was completely blocked by an EGFR kinase inhibitor, AG-1478. BTC also phosphorylated ErbB2 at Tyr877, Tyr1112, and Tyr1248 and induced association of ErbB2 with EGFR, suggesting their heterodimerization in VSMCs. In postreceptor signal transduction, BTC stimulated phosphorylation of extracellular signal-regulated kinase (ERK)1/2, Akt, and p38 mitogen-activated protein kinase (MAPK). Moreover, BTC stimulated proliferation and migration of VSMCs. ERK and Akt inhibitors suppressed migration markedly and proliferation partially, whereas the p38 inhibitor suppressed migration partially but not proliferation. In addition, we found the presence of endogenous BTC in conditioned medium of VSMCs and an increase of BTC on angiotensin II stimulation. In summary, BTC promotes growth and migration of VSMCs through activation of EGFR, ErbB2, and downstream serine/threonine kinases. Together with the expression and processing of endogenous BTC in VSMCs, our results suggest a critical involvement of BTC in vascular remodeling.

Genomic structure and promoter characterization of the gene encoding the ErbB ligand betacellulin

Betacellulin (BTC) belongs to the epidermal growth factor (EGF) family of peptide ligands that are characterized by a six-cysteine consensus motif (EGF-motif) that forms three intra-molecular disulfide bonds, crucial for binding the ErbB receptor family. A variety of in vitro studies have identified BTC as an important factor in the growth and/or differentiation of pancreatic islet cells. The molecular mechanisms that regulate the transcription of the BTC gene however have not been delineated. As an initial step, we have characterized the genomic structure of the mouse BTC (mBTC) gene. mBTC cDNA was used as a probe to screen a mouse 129/SVJ genomic bacterial artificial chromosome (BAC) library. Three positive clones containing the entire gene were isolated. DNA sequence analysis identified six exons (1-6) and five introns (A-E); a structure conserved among the EGF family. PCR analysis showed that introns A-E are approximately 7.8, 8.9, 3.8, 1.4 and 1.4 kb in length, respectively. The EGF-motif is encoded by exons 3 and 4 with an intron (intron C) disrupting the coding sequence between the second and third disulfide loops. All exon-intron boundaries are consistent with the "gt-ag" rule. Multiple transcription start sites and one poly(A) site, located 18 bp downstream of a polyadenylation signal sequence, were identified by 5'- and 3'-RACE, respectively. Approximately 2.6 kb of 5'-flanking region was sequenced and was shown to lack consensus TATA and CCAAT boxes, but was found to contain several putative cis-acting regulatory elements. These included consensus binding sites for transcription factors HNF3 beta, USF, Nkx2-5, AP-4, and Sp1. Functional promoter analysis of the 5'-flanking region in COS-7 cells, using 5'-deletion fragments (-168/+335; -635/+335; -732/+335; -1175/+335; -1698/+335) cloned into a promoterless firefly luciferase reporter vector, identified basal promoter activity and both positive and negative cis-acting elements.