Independent Promoters Regulate the Expression of Two Amino Terminally Distinct Forms of Latent Transforming Growth Factor-β Binding Protein-1 (LTBP-1) in a Cell Type-specific Manner*
- From the ‡Department of Virology, The Haartman Institute, University of Helsinki, FIN-00014 Helsinki, Finland
Abstract
Latent transforming growth factor-β (TGF-β)-binding proteins (LTBPs) are components of the extracellular matrix and large latent TGF-β complexes are secreted by various cells. Human LTBP-1 is known to exist in different forms. LTBP-1L (long) has an amino-terminal extension, which is not found in the smaller LTBP-1S isoform. To study the formation and transcriptional regulation of LTBP-1S and LTBP-1L isoforms, we determined the nucleotide sequences of their 5′-flanking regions. The upstream regions of both isoforms are devoid of TATA boxes but contain other putative binding sites for several transcription factors. Genomic sequencing revealed that LTBP-1L transcript is alternatively spliced to an internal splice acceptor inside exon 1 ofLTBP-1S and thus defined the genomic organization of the isoforms. Reporter gene analysis of upstream regions indicated the presence of independent, functional promoters, which regulate the transcription of the isoforms by cell-specific manner. Deletion analyses of the promoter regions revealed specific elements modulating their basal and cell type-specific expression. In SV-40 virus-transformed WI-38 lung fibroblasts a regulatory element repressed the transcription of LTBP-1S by a cell-specific manner. In amniotic epithelial cells, transcription of the LTBP-1Sreporter gene construct was down-regulated by a distal upstream element. mRNA levels of the isoforms of LTBP-1 were stimulated in response to TGF-β1 in WI-38 cells. However, since TGF-β1 failed to stimulate the transcription of LTBP-1reporter gene constructs, TGF-β1 may mediate the induction of the isoforms by post-transcriptional mechanisms. Chromosomal localization of the LTBP-1 gene was refined to 2p22–24.
Footnotes
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↵* This work was supported by the Academy of Finland, Sigrid Juselius Foundation, Finnish Cancer Organization, Helsinki University Hospital, Novo Nordisk Foundation, Biocentrum Helsinki, and the University of Helsinki.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) and .
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↵§ To whom correspondence should be addressed: The Haartman Institute, Dept. of Virology, P. O. Box 21 (Haartmaninkatu 3), FIN-00014, University of Helsinki, Finland. E-mail: Jorma.Keski-Oja@Helsinki.Fi; Tel.: 358-9-191-26476; Fax: 358-9-191-26475.
- Abbreviations:
- TGF-β
-
transforming growth factor-β
- LTBP
-
latent transforming growth factor-β binding protein
- LTBP-1L
-
long form of LTBP-1
- LTBP-1S
-
short form of LTBP-1
- EGF
-
epidermal growth factor
- VEGF
-
vascular endothelial growth factor
- kb
-
kilobase(s)
- PCR
-
polymerase chain reaction
- bp
-
base pair(s)
- CREB
-
cAMP response element-binding protein
- NF-κB
-
nuclear factor κB
- Oct-1
-
octomer-binding protein-1
- HA cells
-
human amniotic epithelial cells
- TIE
-
TGF-β inhibitory element
- TCE
-
TGF-β responsive control element
- SBE
-
Smad-binding element
-
- Received June 18, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
