Kd. Burns et al., ROLE OF CYTOCHROME-P-450 EPOXYGENASE METABOLITES IN EGF SIGNALING IN RENAL PROXIMAL TUBULE, American journal of physiology. Cell physiology, 38(4), 1995, pp. 831-840
Epidermal growth factor (EGF) is a potent epithelial cell mitogen and
induces eicosanoid production in many cell types. The present study ex
amined signaling mechanisms for EGF in the renal proximal tubule, wher
e high concentrations of cytochrome P-450 epoxygenase have been report
ed. In primary cultures of rabbit proximal tubule cells, EGF (30 nM) i
ncreased endogenous epoxyeicosatrienoic acid (EET) levels 5.3 +/- 1.4-
fold within 10 min (n = 6). In these cells EGF-stimulated [H-3]thymidi
ne incorporation was significantly inhibited by the cytochrome P-450 i
nhibitors ketoconazole or clotrimazole but not by the cyclooxygenase i
nhibitor indomethacin. In fura 2-loaded proximal tubule cells, EGF cau
sed a concentration-dependent increase in cytosolic Ca2+ concentration
([Ca2+](i)), due to Ca2+ influx, which was inhibited by either ketoco
nazole or SKF-525A but not by indomethacin. Addition of 5,6-EET (0.5 m
u M) also induced Ca2+ influx in proximal tubule cells, whereas 8,9-,1
1,12-, or 14,15-EET did not. In cells treated with bis(2-amino-5-methy
lphenoxy)ethane N,N,N ', N'-tetraacetic acid tetraacetoxy-methyl ester
to chelate [Ca2+](i), EGF-stimulated [H-3]thymidine incorporation was
significantly inhibited. Pretreatment of cells with 5.6-EET also augm
ented EGF-stimulated [H-3]thymidine incorporation. These results indic
ate that EGF increases EET levels in proximal tubule and suggest that
5,6-EET or its metabolites may be a modulator of EGF-induced[Ca2+](i)
increases and involved in mitogenesis.