Heregulin and forskolin-induced cyclin D3 expression in Schwann cells: Role of a CCAAT promoter element and CCAAT enhancer binding protein

✍ Scribed by Luis Fuentealba; Charles Schworer; Allen Schroering; Mohammed Rahmatullah; David J. Carey

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 378 KB
• Volume: 45
• Category: Article
• ISSN: 0894-1491
• DOI: 10.1002/glia.10325

✦ Synopsis

Abstract

Heregulin, a polypeptide growth factor, and forskolin, an adenylyl cyclase activator, synergistically stimulate expression of cyclin D3 and cell division in Schwann cells. Heregulin induces expression in Schwann cells of a luciferase reporter gene linked to the cyclin D3 promoter. Forskolin markedly augments reporter expression in the presence of heregulin. Deletion analysis identified several promoter sites that contribute to high‐level reporter expression in heregulin‐ and forskolin‐treated Schwann cells. A promoter fragment that contains 103 bp of 5′‐flanking sequence produced significant reporter expression in heregulin‐ and forskolin‐stimulated cells. Deletion of a consensus CCAAT site within this promoter fragment caused a nearly complete loss of reporter expression. Similar results were obtained when CCAAT site mutations were introduced into the promoter. Heregulin and forskolin increased steady‐state levels of CCAAT/enhancer binding protein‐β (C/EBPβ) in Schwann cells. Mobility shift assays identified proteins in Schwann cell nuclear extracts that formed stable complexes with the cyclin D3 CCAAT promoter element and were disrupted by anti‐C/EBPβ antibody. Transfection of Schwann cells with C/EBPβ cDNA increased cyclin D3 reporter expression. In contrast to these results, mutation of a cAMP response element in the cyclin D3 promoter had only a modest effect on heregulin‐ and forskolin‐stimulated reporter expression. These findings demonstrate that C/EBPβ plays a key role in the heregulin and cAMP‐dependent regulation of cyclin D3 expression in Schwann cells. © 2003 Wiley‐Liss, Inc.