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Induced expression of the endogenous beta interferon gene in adenovirus type 5-transformed rat fibroblasts
U Nielsch1, R Pine, S G Zimmer
1Laboratory of Molecular Cell Biology, Rockefeller University, New York, New York 10021.
Abstract:
Tumorigenesis is a multistep process involving both genetic and epigenetic changes resulting in altered cellular gene expression. While many phenotypic attributes of transformed cells have been described, the cellular genes responsible for these phenotypes are largely unknown. In this study, we show that the interferon-stimulated gene (ISG) ISG15 is expressed in all adenovirus type 5 (Ad5)-transformed rodent cells tested, in an E1A-dependent manner. We find that the level of ISG15 mRNA correlates with the level of the transcription factor ISGF3, which has been postulated to be the transcriptional activator of ISGs. Consistent with the activation of the interferon transduction pathway in Ad5-transformed cells, beta interferon mRNA is expressed in all but the parental untransformed cell line. The level of ISG15 mRNA in Ad5-transformed cells correlated inversely with the ability of these cells to proliferate in soft agar. This appears to have functional significance, since the phenotype of poor growth in agar could be conferred upon a cell line that grows efficiently in soft agar by using conditioned media from cells that grow poorly in soft agar. The same effect could be mimicked by applying rat interferon. We conclude that the degree of activation of the interferon signal transduction pathway explains differences in the transformation phenotypes among Ad5-transformed cell lines.
Insights
Interferon-stimulated gene 15 (ISG15) expression in adenovirus-transformed cells correlates with interferon pathway activation and inversely impacts tumor cell growth in soft agar, explaining transformation phenotype variations.
Area of Science:
- Molecular Biology
- Virology
- Cancer Research
Background:
- Tumorigenesis involves genetic and epigenetic alterations, but responsible genes remain largely unknown.
- Phenotypic changes in transformed cells are complex and not fully understood.
- Adenovirus type 5 (Ad5) transformation provides a model for studying tumorigenesis.
Purpose of the Study:
- To investigate the role of interferon-stimulated genes (ISGs) in Ad5-transformed cells.
- To identify specific genes and pathways involved in Ad5-induced cell transformation.
- To correlate gene expression with cellular phenotypes like soft agar proliferation.
Main Methods:
- Analysis of ISG15 mRNA expression in Ad5-transformed rodent cells.
- Correlation of ISG15 levels with the transcription factor ISGF3 and beta interferon mRNA.
- Assessment of cell proliferation in soft agar.
- Experimental manipulation using conditioned media and rat interferon.
Main Results:
- ISG15 is expressed in all Ad5-transformed cells in an E1A-dependent manner.
- ISG15 mRNA levels correlate with ISGF3 levels, indicating interferon pathway activation.
- Higher ISG15 expression inversely correlates with soft agar colony formation.
- Interferon treatment mimics the effect of conditioned media on growth inhibition.
Conclusions:
- The degree of interferon signal transduction pathway activation explains phenotypic differences in Ad5-transformed cells.
- ISG15 expression is a key factor modulated by the interferon pathway in transformed cells.
- Interferon signaling plays a significant role in regulating the transformation phenotype of Ad5-infected cells.