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Expression of a growth arrest specific gene (gas-1) in transformed cells
1Istituto Patologia Generale, Centro di Studio sulla Patologia Cellulare del CNR, Milano, Italy.
Abstract:
A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. We report the analysis of the expression of one of them (gas-1) in transformed cells. We found a down regulation of gas-1 expression in NIH 3T3 cells transfected in vitro with an activated Ha-ras oncogene. In five chemically-induced mouse tumours grown in vivo the amounts of gas-1 mRNA were largely different but not related to the proliferating activity (evaluated by both H3 histone expression and 3H-thymidine incorporation into DNA). The amount of gas-1 mRNA in the tumours was in general higher than in normal tissues. Expression of c-myc was also evaluated and found to be high in tumours which exhibited low gas-1 expression. Two fibrosarcomas, CA-2 and CB-20, with similar phenotype, similar growth rate, different expression of c-myc and 100-fold difference in gas-1 expression were further investigated and gas-1 expression was found to be correlated with the expression of a differentiated function (as judged from collagen expression). Cell lines derived from CA-2 and CB-20 and maintained under different culture conditions showed that the cell cycle regulation and serum response of gas-1 expression were lost in CA-2. The higher steady state level of gas-1 mRNA in spite of a shorter mRNA half life suggests that in CB-20 cells the gas-1 gene is transcribed faster than in CA-2 cells indicating that transcriptional regulation is the major determinant of gas-1 gene expression in tumour cells. The finding of gas-1 expression in tumour cells suggests that its expression is not sufficient to maintain cells into quiescence, however, as a marker specific for the G0 phase, it could be useful, in conjunction with other growth related genes, to define the cell cycle distribution of a cell population.
Insights
Growth arrest-specific gene 1 (gas-1) expression is altered in cancer cells, showing decreased levels with oncogene activation. Its expression in tumors correlates with differentiation, not proliferation, suggesting transcriptional regulation is key.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Cycle Regulation
Background:
- Growth arrest-specific (gas) genes are identified as being negatively regulated by serum.
- The study focuses on the expression of gas-1, a specific gene within this group, in the context of cellular transformation.
Purpose of the Study:
- To analyze the expression of the gas-1 gene in transformed cells and chemically-induced mouse tumors.
- To investigate the relationship between gas-1 expression, proliferation, differentiation, and oncogene activity.
Main Methods:
- Quantitative analysis of gas-1 mRNA levels in NIH 3T3 cells transfected with Ha-ras oncogene.
- Evaluation of gas-1 mRNA in chemically-induced mouse tumors, alongside proliferation markers (H3 histone, 3H-thymidine incorporation) and c-myc expression.
- Detailed investigation of two fibrosarcoma cell lines (CA-2, CB-20) with varying gas-1 and c-myc expression, assessing correlation with collagen expression and cell cycle regulation.
Main Results:
- Down-regulation of gas-1 expression was observed in NIH 3T3 cells with activated Ha-ras.
- gas-1 mRNA levels in tumors varied but did not correlate with proliferation; generally higher than in normal tissues.
- Tumors with low gas-1 expression showed high c-myc expression. gas-1 expression correlated with differentiated function (collagen) in fibrosarcomas.
- Cell cycle regulation and serum response of gas-1 were lost in the CA-2 cell line.
- Transcriptional regulation was identified as the primary determinant of gas-1 gene expression in tumor cells, indicated by faster transcription in CB-20 despite shorter mRNA half-life.
Conclusions:
- gas-1 expression in tumor cells is not sufficient to induce quiescence.
- gas-1 serves as a potential marker for the G0 phase.
- gas-1, alongside other growth-related genes, could aid in defining cell cycle distribution within cell populations.