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DNA synthesis in U-2 OS human osteosarcoma cells is independent of PDGF binding to functional cell surface receptors
1Department of Periodontics, University of Texas Health Science Center, San Antonio 78284.
Abstract:
Previous studies have shown that suramin reveals specific PDGF binding sites on U-2 OS human osteosarcoma cells. Studies presented here indicate that U-2 OS cells pretreated with suramin internalize and degrade 125I-PDGF and respond to PDGF by increased tyrosine kinase activity and amino acid transport. However, DNA synthesis in these cells is not reduced by incubation with the PDGF blocking agent suramin and is not stimulated by exogenous PDGF. These data indicate that U-2 OS cells possess functional PDGF receptors but that high levels of DNA synthesis in these cells is unrelated to the binding of secreted PDGF to these cell surface receptors. Thus, it is unlikely that the PDGF mitogen produced by U-2 OS cells stimulates proliferation through an autocrine mechanism involving secretion and subsequent binding to PDGF receptors.
Insights
U-2 OS cells have functional platelet-derived growth factor (PDGF) receptors, but their high DNA synthesis is independent of PDGF binding. This suggests PDGF does not stimulate proliferation via an autocrine mechanism in these osteosarcoma cells.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- Previous research identified specific platelet-derived growth factor (PDGF) binding sites on U-2 OS human osteosarcoma cells using suramin.
- U-2 OS cells are a human osteosarcoma cell line used to study cell growth and signaling pathways.
Purpose of the Study:
- To investigate the functional role of PDGF receptors in U-2 OS cells.
- To determine if PDGF signaling mediates DNA synthesis and proliferation in U-2 OS cells.
- To explore the potential autocrine mechanism of PDGF in osteosarcoma growth.
Main Methods:
- Treatment of U-2 OS cells with suramin, a PDGF antagonist.
- Incubation with radiolabeled 125I-PDGF to assess internalization and degradation.
- Measurement of tyrosine kinase activity and amino acid transport in response to PDGF.
- Assessment of DNA synthesis levels under various experimental conditions.
Main Results:
- U-2 OS cells pretreated with suramin internalized and degraded 125I-PDGF.
- PDGF stimulation led to increased tyrosine kinase activity and amino acid transport.
- Suramin did not reduce, and exogenous PDGF did not stimulate, DNA synthesis in these cells.
- U-2 OS cells possess functional PDGF receptors, but DNA synthesis is not linked to PDGF binding.
Conclusions:
- U-2 OS cells exhibit functional PDGF receptors, but their high DNA synthesis rate is independent of PDGF.
- The study refutes an autocrine mechanism where secreted PDGF stimulates proliferation via cell surface receptors in U-2 OS cells.
- These findings suggest alternative pathways regulate DNA synthesis and proliferation in this osteosarcoma cell line.