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Increased proteinase expression during tumor progression of cell lines down-modulated for TIMP levels: a new
R Khokha1, P Waterhouse, P Lala
1Cancer Research Laboratory, University of Western Ontario, London, Canada.
Abstract:
We have reported that down-modulation of tissue inhibitor of metalloproteinases (TIMP) by means of antisense RNA converts non-tumorigenic Swiss 3T3 cells into malignant cells capable of forming metastasizing tumors in nude mice [Science 243:947 (1989)]. We now describe changes in the expression of specific genes associated with tumor progression of two lines down-modulated with TIMP, LA1 and LA7. Six independent variant cell lines, generated from different primary tumors produced by LA1 and LA7, lacked (like LA1 and LA7) many characteristics of typical transformed cells. However, their tumorigenicity in nude mice was enhanced; tumors appeared with a shorter lag (1-3 weeks versus 8-10 weeks for the parental clones, LA1 and LA7) and grew very rapidly. Increases, substantial in some cases, in the expression of a cysteine proteinase, cathepsin L, and metalloproteinases homologous to rat transin (stromelysin) and transin-2 were characteristic of these variant clones. The mRNA levels encoding the transformation-associated secreted phosphoprotein (osteopontin) and the calcium-binding protein calcyclin were also augmented. No evidence for gene amplification was found, and we did not detect any change in the mRNA levels of the proto-oncogenes that were examined. These novel cell lines represent a new paradigm for the transformed cell. Our data suggest that a reduction in TIMP secretion enhances the cell's oncogenic capacity by altering the extracellular environment in a way conducive to further changes in gene expression necessary for tumor progression.
Insights
Reducing tissue inhibitor of metalloproteinases (TIMP) enhances cancer cell malignancy. New cell lines show increased tumor growth and metastasis due to altered gene expression, offering a new model for cancer progression.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- Down-modulation of tissue inhibitor of metalloproteinases (TIMP) using antisense RNA transforms non-tumorigenic cells into malignant cells capable of forming metastatic tumors.
- Previous studies established the link between TIMP reduction and cellular malignancy.
Purpose of the Study:
- To investigate gene expression changes in cell lines with down-modulated TIMP that exhibit enhanced tumorigenicity.
- To characterize novel cell lines derived from tumors produced by TIMP-down-modulated cells.
Main Methods:
- Generation and characterization of six independent variant cell lines from primary tumors of LA1 and LA7 TIMP-down-modulated cells.
- Analysis of gene expression, including cysteine proteinase (cathepsin L), metalloproteinases (stromelysin, transin-2), osteopontin, and calcyclin mRNA levels.
- Assessment of tumorigenicity and tumor growth rates in nude mice.
Main Results:
- Variant cell lines exhibited enhanced tumorigenicity with shorter lag times and rapid growth in nude mice compared to parental clones.
- Significant increases in cathepsin L, stromelysin, transin-2, osteopontin, and calcyclin mRNA levels were observed in variant clones.
- No evidence of gene amplification or changes in proto-oncogene mRNA levels was detected.
Conclusions:
- These novel cell lines represent a new paradigm for transformed cells, demonstrating enhanced oncogenic capacity.
- Reduced TIMP secretion promotes tumor progression by altering the extracellular environment, facilitating further gene expression changes.
- The findings suggest a mechanism where extracellular matrix remodeling by proteases contributes to cancer progression.