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Reduction in platelet-derived growth factor receptor mRNA in v-src-transformed fibroblasts
Q X Zhang1, F Walker, A W Burgess
1Ludwig Institute for Cancer Research, Melbourne Tumour Biology, Royal Melbourne Hospital, Vic., Australia.
Abstract:
The status of the platelet-derived growth factor (PDGF) receptor in normal rat kidney (NRK) fibroblasts and in NRK fibroblasts transformed by the v-src oncogene or the polyoma middle T (pmt) antigen has been compared. v-src-NRK cells have 7-fold fewer surface binding sites for PDGF than NRK cells, but the affinity of the residual receptors for PDGF is reduced only 2-fold. Levels of the PDGF receptor measured by Western blotting or in an autophosphorylation assay in vitro are 8- and 4-fold lower respectively in v-src-NRK cells than in NRK cells. No PDGF-induced phosphorylation of the PDGF receptor is apparent after 32P-labelling of intact v-src-NRK cells, implying that the reduction in PDGF receptor levels is not a consequence of production of autocrine PDGF. A 10-fold reduction in the amount of mRNA for the PDGF receptor is also observed in v-src-NRK cells. No decrease in PDGF receptor protein or mRNA levels is observed in pmt-NRK cells. We conclude that levels of the PDGF receptor in v-src-transformed NRK fibroblasts are modulated by reduction in the level of PDGF receptor mRNA.
Insights
v-src oncogene transformation reduces platelet-derived growth factor (PDGF) receptors in NRK fibroblasts by decreasing PDGF receptor mRNA levels. This impacts PDGF receptor status and signaling in cancer research.
Area of Science:
- Cell Biology
- Molecular Oncology
- Signal Transduction
Background:
- Platelet-derived growth factor (PDGF) receptors are crucial for normal cell function.
- Oncogenic transformation can alter growth factor receptor expression and signaling.
- Understanding these alterations is key to cancer research.
Purpose of the Study:
- To compare PDGF receptor status in normal rat kidney (NRK) fibroblasts versus v-src or polyoma middle T (pmt) antigen-transformed NRK cells.
- To investigate the mechanisms underlying changes in PDGF receptor levels upon oncogenic transformation.
Main Methods:
- Quantification of PDGF surface binding sites.
- Western blotting for PDGF receptor protein levels.
- In vitro autophosphorylation assays.
- Analysis of PDGF receptor mRNA levels.
- Radiolabeling studies (32P) to assess receptor phosphorylation.
Main Results:
- v-src-NRK cells exhibited a 7-fold decrease in PDGF binding sites and reduced receptor affinity.
- PDGF receptor protein and mRNA levels were significantly lower (8-fold and 10-fold, respectively) in v-src-NRK cells.
- No significant changes in PDGF receptor levels were observed in pmt-NRK cells.
- PDGF-induced receptor phosphorylation was absent in v-src-NRK cells.
Conclusions:
- v-src oncogene transformation downregulates PDGF receptor levels in NRK fibroblasts.
- The primary mechanism for this downregulation is a reduction in PDGF receptor mRNA.
- pmt antigen transformation does not affect PDGF receptor levels, suggesting pathway-specific effects.