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Neoplastic transformation inactivates specific trans-acting factor(s) required for the expression of the
V E Avvedimento1, A Musti, A Fusco
1Dipartimento di Biologia e Patologia Molecolare, II Facolta di Medicina e Chirurgia, Universita di Napoli, Italy.
Abstract:
The expression of rat thyroglobulin gene is repressed following the transformation of rat thyroid cells with Kirsten murine sarcoma virus. The expression of a reporter gene fused to the thyroglobulin promoter is down-regulated in transformed thyroid cells in transient or in stable transfection assays. DNase and exonuclease III cleavage-protection analysis reveals that a promoter binding activity located at -60 base pairs from the transcription start site is substantially reduced in transformed thyroid cells. The repression in the transformed cells of the reporter gene joined to the thyroglobulin promoter can be reversed by fusion with normal differentiated thyroid cells. Fusion of transformed thyroid cells to liver cells does not reactivate the reporter under control of the thyroglobulin promoter.
Insights
Thyroid cell transformation with Kirsten murine sarcoma virus represses thyroglobulin gene expression. This repression is linked to reduced promoter binding activity and can be reversed by fusion with normal thyroid cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Thyroglobulin gene expression is crucial for thyroid function.
- Viral transformation of thyroid cells can alter gene expression patterns.
- Kirsten murine sarcoma virus (KiMSV) is known to induce cellular transformation.
Purpose of the Study:
- To investigate the effect of KiMSV transformation on rat thyroglobulin gene expression.
- To identify the molecular mechanisms underlying the repression of thyroglobulin gene expression in transformed thyroid cells.
- To explore the potential for reversing the repressed gene expression.
Main Methods:
- Transient and stable transfection assays using a reporter gene fused to the thyroglobulin promoter.
- DNase and exonuclease III cleavage-protection assays to analyze promoter binding activity.
- Cell fusion experiments between transformed and normal differentiated thyroid cells, and with liver cells.
Main Results:
- KiMSV transformation significantly down-regulates reporter gene expression driven by the thyroglobulin promoter.
- A key promoter binding activity at -60 base pairs is substantially reduced in transformed thyroid cells.
- Fusion with normal differentiated thyroid cells reverses the repression of thyroglobulin promoter activity.
Conclusions:
- KiMSV-induced transformation represses thyroglobulin gene expression in rat thyroid cells.
- Reduced binding of a specific transcription factor at the thyroglobulin promoter is a key mechanism of repression.
- Cellular differentiation and specific cell-cell interactions play a role in maintaining or restoring thyroglobulin gene expression.