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Binding of insulin-like growth factors to Tera-2 human embryonal carcinoma cells during differentiation
J F Fleck1, G W Sledge, S V Benenati
1Department of Medicine, Indiana University School of Medicine, Indianapolis.
Abstract:
Differentiation of Tera-2 human embryonal carcinoma cells by exposure to 2.1 mM alpha-difluoromethylornithine resulted in changes in morphology, a decrease in growth rate, and changes in the expression of SSEA-1 differentiation antigen. While the binding of 125I-insulin-like growth factor I (IGF-I) remained relatively constant during differentiation, binding of 125I-IGF-II increased 2-3-fold. Further, the binding of IGF-II was 87 times greater than IGF-I in both undifferentiated and differentiated cells. Undifferentiated Tera-2 cells exhibited a single class of binding sites for both IGF-I (KD = 1.2 nM, 7.0 x 10(3) sites/cell) and IGF-II (KD = 8.3 nM, 3.4 x 10(5) sites/cell). Following differentiation, IGF-I continued to bind to a single class of binding sites (KD 1.0 nM, 6.7 x 10(3) sites/cell) whereas IGF-II bound to both high-affinity sites (KDH 0.3 nM, 2.2 x 10(5) sites/cell) and low-affinity sites (KDL 15.1 nM, 1.6 x 10(7) sites/cell). The binding of iodinated IGF-II was blocked by unlabeled IGF-II but not IGF-I. In contrast, 125I-IGF-I binding was prevented by either IGF-I or IGF-II. Affinity cross-linking experiments demonstrated the presence of both type I and type II IGF receptors along with a number of IGF binding proteins. IGF-I failed to stimulate the incorporation of [3H]thymidine in both undifferentiated and differentiated cells. Although IGF-II caused a significant increase in [3H]thymidine incorporation in both undifferentiated and differentiated Tera-2 cells, the magnitude of the response and the sensitivity of the cells to IGF-II stimulation was diminished following differentiation. The observed changes in IGF-II binding, which occur in conjunction with cellular differentiation, may be an important feature of the expression of the differentiated phenotype by human germ cell tumors.
Insights
Alpha-difluoromethylornithine induced differentiation in Tera-2 cells, altering morphology and growth. Insulin-like growth factor II (IGF-II) binding increased significantly, suggesting a role in germ cell tumor differentiation.
Area of Science:
- Endocrinology
- Cell Biology
- Developmental Biology
Background:
- Tera-2 human embryonal carcinoma cells serve as a model for studying germ cell tumor differentiation.
- Insulin-like growth factors (IGFs) play crucial roles in cell growth, differentiation, and development.
- Understanding IGF signaling is vital for comprehending the mechanisms underlying tumor progression and differentiation.
Purpose of the Study:
- To investigate the effects of alpha-difluoromethylornithine-induced differentiation on IGF binding and signaling in Tera-2 cells.
- To characterize the binding kinetics and receptor interactions of IGF-I and IGF-II during cellular differentiation.
- To explore the functional consequences of altered IGF binding on cellular proliferation.
Main Methods:
- Induction of Tera-2 cell differentiation using alpha-difluoromethylornithine.
- Radioligand binding assays using 125I-IGF-I and 125I-IGF-II to quantify binding.
- Affinity cross-linking studies to identify IGF receptors and binding proteins.
- Measurement of [3H]thymidine incorporation to assess DNA synthesis.
Main Results:
- Differentiation led to morphological changes, decreased growth rate, and altered SSEA-1 expression.
- IGF-II binding increased 2-3 fold, with significantly higher affinity and capacity post-differentiation.
- IGF-I binding remained constant, while IGF-II stimulated proliferation, albeit with reduced sensitivity after differentiation.
- Both type I and type II IGF receptors were identified, along with IGF binding proteins.
Conclusions:
- Differentiation of Tera-2 cells significantly alters IGF-II receptor binding characteristics.
- Increased IGF-II binding and signaling may be a key feature in the differentiated phenotype of human germ cell tumors.
- These findings highlight the complex interplay between IGFs and cellular differentiation in the context of cancer development.