Heregulin and forskolin-induced cyclin D3 expression in Schwann cells: role of a CCAAT promoter element and CCAAT enhancer binding protein.
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-beta (C/EBPbeta) 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/EBPbeta antibody. Transfection of Schwann cells with C/EBPbeta 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/EBPbeta plays a key role in the heregulin and cAMP-dependent regulation of cyclin D3 expression in Schwann cells.
Fuentealba
Luis
L
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822-2601, USA.
Schworer
Charles
C
Schroering
Allen
A
Rahmatullah
Mohammed
M
Carey
David J
DJ
D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D056743:Cyclin D3; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D020890:Neuregulin-1 / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012583:Schwann Cells / Q000187:drug effects* / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; C534698:Ccnd3 protein, rat; D056743:Cyclin D3; D016213:Cyclins; D020890:Neuregulin-1; D005576:Colforsin