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Correlation between suppression of c-myc and antiproliferative effect of transforming growth factor-beta 1 in thyroid
1Department of Cell Physiology, Nagasaki University School of Medicine, Japan.
Abstract:
The growth regulatory activity of transforming growth factor-beta 1 (TGF beta 1) was studied in a clonal strain of thyroid papillary carcinoma cell (NPA). Despite the presence of TGF beta 1 and its receptor messenger RNA in thyroid carcinoma, the molecular mechanism of TGF beta 1 action on cell growth of thyroid carcinoma has not yet been elucidated. Exogenously added TGF beta 1 inhibited DNA synthesis and cell growth in a dose- and time-dependent manner at concentrations of 0.1-10 ng/ml. TGF beta 1 inhibited not only basal but also fetal bovine serum-stimulated cell proliferation. Steady state levels of c-myc messenger RNA transcripts were inhibited by TGF beta 1 after 0.5-h treatment. Antisense, but not sense, c-myc oligodeoxynucleotides also caused suppression of NPA cell growth in a dose-responsive manner. Transfection studies of the 5'-up-stream flanking region (UFR) of c-myc/chloramphenicol acetyltransferase chimera genes suggest the presence of a TGF beta 1-responsive DNA element in the 2.3-kilobase c-myc 5'-UFR. Deletion mutant studies indicate the element lies between -106 to 70 relative to the P1 transcription start site. Studies with the gel mobility shift assay using 23-basepair double strand DNA showed the presence of at least two nuclear factors in NPA cell. TGF beta 1 treatment did not cause any alteration in TGF beta 1-induced mobility; however, the reduction of a positive band was selectively observed during 30 min to 2 h after treatment with TGF beta 1. In contrast, the position and intensity of another band were not altered by TGF beta 1 treatment. These results demonstrate that the inhibition of a nuclear factor binding to the c-myc 5'-UFR and subsequent suppression of c-myc gene expression are directly involved in the antiproliferative action of TGF beta 1 in NPA cell growth.
Insights
Transforming growth factor-beta 1 (TGF beta 1) inhibits thyroid papillary carcinoma cell growth by suppressing c-myc gene expression. This antiproliferative action involves reduced binding of nuclear factors to the c-myc upstream regulatory region.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Thyroid papillary carcinoma (NPA) cells possess transforming growth factor-beta 1 (TGF beta 1) and its receptor mRNA.
- The precise molecular mechanisms of TGF beta 1's effect on thyroid carcinoma cell proliferation remain unclear.
Purpose of the Study:
- To investigate the growth regulatory activity of TGF beta 1 in NPA cells.
- To elucidate the molecular pathways through which TGF beta 1 influences thyroid carcinoma cell growth.
Main Methods:
- Cell proliferation assays with varying TGF beta 1 concentrations and durations.
- Analysis of c-myc messenger RNA (mRNA) transcript levels.
- Oligodeoxynucleotide transfection studies targeting c-myc.
- Reporter gene assays using c-myc promoter-chloramphenicol acetyltransferase (CAT) chimeras.
- Gel mobility shift assays to study nuclear factor binding.
Main Results:
- TGF beta 1 significantly inhibited NPA cell DNA synthesis and proliferation in a dose- and time-dependent manner.
- TGF beta 1 reduced steady-state levels of c-myc mRNA, an effect mimicked by antisense c-myc oligodeoxynucleotides.
- Reporter gene studies identified a TGF beta 1-responsive element within the c-myc 5'-upstream regulatory region (-106 to 70).
- Gel mobility shift assays revealed TGF beta 1 treatment reduced the binding of at least one nuclear factor to this c-myc regulatory element.
Conclusions:
- TGF beta 1 exerts an antiproliferative effect on thyroid papillary carcinoma cells.
- The inhibition of c-myc gene expression, mediated by altered nuclear factor binding to its regulatory region, is a key mechanism underlying TGF beta 1's action.