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Down-regulated proteins of mesenchymal tumor cells
1MEM-Institute, University of Bern, Switzerland.
Abstract:
To identify proteins that are lost during the establishment of the transformed phenotype of a tumor cell, we have prepared a subtracted cDNA library with mRNA from normal human fibroblasts and from their matched SV40 transformed counterparts. More than 40 clones were obtained that showed a dramatic reduction in their relative expression after oncogenic transformation. The proteins encoded by these clones could be grouped into four distinct classes: extracellular matrix proteins (fibronectin, beta ig-h3, collagen VI), enzymes (collagenase, urokinase), cytoskeletal proteins (vinculin, SM22) and regulatory proteins (beta-glycan, integrin-associated protein, myosin kinase, IGFBP-5). Six novel gene products were discovered during these experiments, including a novel serine protease, a zyxin-like protein, an ankyrin-like protein and a GTP-binding protein. Only four of all the transformation-sensitive cDNAs were consistently down-regulated when a variety of cell lines derived from spontaneous mesenchymal tumors was investigated: beta ig-h3, collagen VI, the novel ankyrin-like protein, and IGFBP-5. It is likely that these gene products play an important role in the maintenance of the normal phenotype.
Insights
Researchers identified proteins lost during tumor cell transformation. Key down-regulated genes like beta ig-h3 and collagen VI may maintain normal cell phenotype.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Tumorigenesis involves significant cellular changes, including alterations in protein expression.
- Understanding protein loss during oncogenic transformation is crucial for identifying tumor suppressors and therapeutic targets.
Purpose of the Study:
- To identify and characterize proteins downregulated during the transition of normal fibroblasts to SV40-transformed cells.
- To determine which of these downregulated proteins are consistently lost in various mesenchymal tumor cell lines.
Main Methods:
- Subtracted cDNA library construction using mRNA from normal and SV40-transformed human fibroblasts.
- Differential screening of cDNA clones to identify genes with reduced expression post-transformation.
- Analysis of transformation-sensitive cDNAs in cell lines derived from spontaneous mesenchymal tumors.
Main Results:
- Over 40 clones showed reduced expression after oncogenic transformation.
- Downregulated proteins included extracellular matrix, enzymes, cytoskeletal, and regulatory proteins.
- Four genes—beta ig-h3, collagen VI, a novel ankyrin-like protein, and IGFBP-5—were consistently downregulated across multiple tumor cell lines.
- Six novel gene products were identified, including a serine protease and a GTP-binding protein.
Conclusions:
- Specific proteins are significantly lost during tumor cell transformation.
- Beta ig-h3, collagen VI, a novel ankyrin-like protein, and IGFBP-5 are likely critical for maintaining the normal cellular phenotype.
- These consistently downregulated genes represent potential biomarkers or therapeutic targets in mesenchymal tumors.