Epidermal growth factor-induced mitogenesis in kidney epithelial cells (LLC-PK1)

The growth kinetics of LLC-PK1 renal epithelia is examined, particularly relating to epidermal growth factor (EGF)-induced mitogenesis in growth-arrested confluent cultures. LLC-PK1 cell proliferation is shown to be density dependent. After reaching confluence, cell number remains near constant, and addition of fresh serum-containing medium does not elicit significant increase in cell number. EGF and 12-O-tetradecanoyl-phorbol-13-acetate do however induce a marked increase in cell number, although each with different kinetics. EGF-induced mitogenesis in LLC-PK1 cells has the following characteristics: (a) DNA synthesis peaks in a defined window 10-12 h after EGF administration; (b) 10 nM EGF elicits a maximal response; (c) 10 nM EGF requires only a 30-s exposure to these cells to induce a maximal mitogenic response; (d) exposure of the basolateral membrane of these polar cells to 10 nM EGF is necessary for mitogenesis, exposure of EGF to the apical surface being ineffective. This aspect of polarity in growth factor-induced mitogenesis is a phenomenon which cannot be addressed with nonpolar fibroblastic cell cultures.