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Differential effects of PDGF isoforms on proliferation of normal rat kidney cells
E J Van Zoelen1, W Van Rotterdam, R A Van de Wetering
1Department of Cell Biology, University of Nijmegen, The Netherlands.
Abstract:
The effects of the PDGF isoforms AA, AB and BB have been studied on the proliferation of normal rat kidney cells, a non-tumorigenic fibroblast cell line which contains both type alpha and type beta PDGF receptors. On monolayer cells made quiescent by serum deprivation, PDGF-AA is a relatively poor mitogen compared to PDGF-AB and PDGF-BB. When these cells are made density-arrested following continuous incubation with epidermal growth factor, however, they can be restimulated to proliferate by all three PDGF isoforms with similar activity when added at sufficiently high concentration, resulting in phenotypic cellular transformation. Binding of radiolabelled isoforms to confluent NRK monolayers obeys the predictions of an induced receptor dimerisation model, and increases in the order AA < AB < BB. Upon preincubation of the cells with PDGF-AA, the dose-response curve for mitogenic activity of PDGF-AB is shifted to higher concentrations, indicating that PDGF-AA can partly antagonize the growth stimulating activity of PDGF-AB, as has also been observed in ligand binding studies. This observation has subsequently been confirmed using fluorescence cytometric analysis. PDGF-AB is highly active in inducing anchorage-independent proliferation of NRK cells, but in all such assays PDGF-AA is at least as potent as PDGF-BB. Intriguingly, PDGF-BB is almost devoid of activity in inducing soft agar growth of these cells, in contrast to PDGF-AA. When compared to substrate-attached cells, enhanced expression of the type alpha PDGF receptor was observed under anchorage-independent conditions. These results show that the relative potency of the three PDGF isoforms to stimulate proliferation of NRK cells is different for quiescent cells in monolayer, density-arrested cells and anchorage-independent cells. Moreover it is shown that the biological activity of PDGFs can be impaired by the additional presence of other isoforms.
Insights
Platelet-derived growth factor (PDGF) isoforms AA, AB, and BB show varied effects on normal rat kidney cell proliferation. PDGF-AA is a weaker mitogen than PDGF-AB and PDGF-BB on quiescent cells, but all isoforms stimulate proliferation in density-arrested cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Platelet-derived growth factor (PDGF) plays a crucial role in cell proliferation and is implicated in various biological processes.
- PDGF exists in several isoforms (AA, AB, BB) that bind to PDGF receptors (alpha and beta), influencing cellular responses.
- Normal rat kidney (NRK) cells possess both PDGF receptor types, making them a suitable model for studying PDGF isoform effects.
Purpose of the Study:
- To investigate the differential mitogenic effects of PDGF-AA, PDGF-AB, and PDGF-BB on NRK cells under various conditions.
- To explore the impact of PDGF isoforms on cell proliferation, receptor binding, and anchorage-independent growth.
- To understand the potential antagonistic interactions between different PDGF isoforms.
Main Methods:
- Utilized normal rat kidney (NRK) cells, a non-tumorigenic fibroblast cell line.
- Assessed cell proliferation using monolayer cultures under quiescent and density-arrested conditions.
- Investigated anchorage-independent proliferation in soft agar assays.
- Employed radioligand binding assays and fluorescence cytometric analysis to study receptor interactions.
Main Results:
- PDGF-AA demonstrated weaker mitogenic activity on quiescent NRK cells compared to PDGF-AB and PDGF-BB.
- All three PDGF isoforms stimulated proliferation in density-arrested NRK cells, leading to phenotypic transformation.
- Ligand binding affinity increased in the order PDGF-AA < PDGF-AB < PDGF-BB.
- PDGF-AA exhibited partial antagonism towards PDGF-AB's mitogenic activity.
- PDGF-AB strongly induced anchorage-independent proliferation, while PDGF-AA was potent, and PDGF-BB showed minimal activity.
- Enhanced expression of the alpha PDGF receptor was observed under anchorage-independent conditions.
Conclusions:
- The mitogenic potency of PDGF isoforms varies significantly depending on the cell state (quiescent, density-arrested, anchorage-independent).
- PDGF isoform interactions can lead to complex biological outcomes, including partial antagonism.
- Differential receptor expression and isoform-specific activities highlight the nuanced regulation of cell proliferation by PDGF.