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Novel non-TGF-beta-binding splice variant of LTBP-4 in human cells and tissues provides means to decrease TGF-beta
K Koli1, J Saharinen, M Kärkkäinen
1Department of Virology, Haartman Institute and Biomedicum Helsinki, University of Helsinki and Helsinki University Hospital, Finland. katri.koli@helsinki.fi
Journal of Cell Science
|October 31, 2001
Summary
Latent transforming growth factor-beta (TGF-beta) binding proteins (LTBPs) associate with TGF-beta. A novel LTBP-4 variant lacking TGF-beta binding capacity was identified, suggesting roles in TGF-beta regulation and extracellular matrix structure.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Small latent TGF-beta complexes involve latency associated peptide (LAP) noncovalently bound to TGF-beta.
- These complexes are secreted and form covalent complexes with latent TGF-beta binding proteins (LTBPs) in the extracellular matrix.
- Four LTBP types (LTBP-1 to -4) have been identified, featuring repetitive sequences, with the 3rd 8-Cys repeat in LTBP-1, -3, and -4 mediating small latent TGF-beta association.
Purpose of the Study:
- To analyze the expression patterns of LTBP-1 to -4 in various human cell lines.
- To investigate the impact of malignant transformation on LTBP expression.
- To identify and characterize novel alternatively spliced LTBP variants and their potential functions.
Main Methods:
- Reverse transcription polymerase chain reaction (RT-PCR) was used to analyze LTBP mRNA expression in cultured human cell lines.
- Cell lines included fibroblasts, endothelial cells, and keratinocytes.
- Sequence analysis was performed to identify alternatively spliced variants.
Main Results:
- LTBPs were expressed in an overlapping manner across different cell types, with variations in expression levels.
- Malignant transformation, exemplified by SV-40 transformed fibroblasts, correlated with decreased LTBP mRNA expression.
- A novel LTBP-4 splice variant, LTBP-4delta8-Cys3rd, lacking the TGF-beta binding 3rd 8-Cys repeat, was identified and found in tissues expressing full-length LTBP-4.
- This variant was generated by alternative splicing over two exons, and another variant lacking a single exon was found in HL-60 cells.
Conclusions:
- The expression of LTBP variants, particularly the non-TGF-beta-binding LTBP-4delta8-Cys3rd, may play a crucial role in regulating TGF-beta deposition in tissues.
- The LTBP-4delta8-Cys3rd protein, as a component of extracellular matrix microfibrils, might also contribute to structural functions independent of TGF-beta signaling.