Epidermal growth factor (EGF) receptor density controls mitogenic activation of normal rat kidney (NRK) cells by EGF
✍ Scribed by D. H. T. P. Lahaye; M. G. M. Camps; P. E. van Erp; P. H. J. Peters; E. J. J. van Zoelen
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 272 KB
- Volume
- 174
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Normal rat kidney (NRK) fibroblasts are immortalized cells that are strictly dependent on externally added growth factors for proliferation. When cultured in the presence of epidermal growth factor (EGF) as the only growth stimulating hormone, these cells have a normal phenotype and undergo density-dependent growth inhibition. It has been postulated that this density-arrest results from a decrease of EGF receptor levels below a threshold level which makes these cells unresponsive to stimulation by EGF. In the present study, we show that NRK cells, made quiescent by serum-deprivation at submaximum density, are mitogenically still responsive to EGF, but show enhanced mitogenic stimulation after 8 hr pre-treatment with either transforming growth factor b (TGFb) or retinoic acid (RA), while prostaglandin F 2a (PGF 2a ) and bradykinin (BK) enhance the mitogenic stimulation by EGF only slightly under these conditions. Addition of TGFb or RA results in an increase of both 125 I-EGF-binding capacity and EGF receptor mRNA levels. Using flow cytometric analysis, we show that pre-treatment with TGFb or RA increases the percentage of cells entering the cell cycle as a function of time. Furthermore, pre-treatment of the cells with TGFb or RA increases the rate of mitogen-activated protein kinase (MAPK) phosphorylation by EGF. PGF 2a and BK also increase EGF receptor levels, but only with delayed kinetics. These results show that already in serum-deprived quiescent NRK cells, EGF receptor levels limit EGF-induced mitogenic stimulation. This observation provides further evidence for the regulating role of the EGF receptor in density-dependent growth control of NRK cells.