Regulation of epidermal growth factor receptor expression and growth by protein kinase C and retinoic acid in LLC-PK1 cells.
The importance of receptor expression and protein kinase C to epidermal growth factor (EGF)-induced cell proliferation was studied in LLC-PK1 kidney cells. These cells have both high- and low-affinity binding sites for EGF. Neither transforming growth factor-beta nor tumor necrosis factor altered EGF receptor expression. On the other hand, retinoic acid induced a concentration-dependent increase in EGF binding that was maximal at 1 mumol/L. One micromolar of retinoic acid increased EGF binding from 0.38 +/- 0.01 fmol/10(6) cells in controls to 1.10 +/- 0.03 fmol/10(6) in treated cells at 18 hours (n = 8, P < 0.001). The increase in binding was the result of an increase in the Bmax of the high-affinity receptor. The upregulation of the EGF receptor induced by retinoic acid was associated with enhanced EGF-induced growth promotion. A 45-minute incubation of cells with phorbol 12-myristate 13-acetate caused a concentration-dependent decrease in EGF binding that was prevented by a 40-hour, 2 mumol/L pre-exposure to phorbol 12-myristate 13-acetate; 10(-8) mol/L EGF also caused a downregulation of the EGF receptor that was not prevented by phorbol 12-myristate 13-acetate or retinoic acid. Downregulation of protein kinase C did not interfere in the capacity of EGF to induce growth in these cells. These studies demonstrate that EGF receptor upregulation plays an important role in the control of EGF-induced cell growth. Protein kinase C regulates EGF binding in these cells; however, it is not necessary for EGF-induced growth promotion or receptor downregulation.
Mantzouris
N M
NM
Department of Internal Medicine, University of Maryland Medical School, Baltimore.
Kaplan
J
J
Clark
G
G
Hise
M K
MK
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors / Q000032:analysis*; D007668:Kidney / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation
D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D014212:Tretinoin; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011493:Protein Kinase C