System A-mediated amino acid transport, activation of
different steps of signal transduction and involvement
of different isoforms of protein kinase C (PKC) have
been investigated in chick embryo hepatocytes after
epidermal growth factor (EGF) stimulation. EGF
rapidly (10 min) increased the rate of aminoisobutyric
acid (AIB) uptake in chick embryo hepatocytes freshly isolated on the
19th day of embryonic life, while no change was detectable at other
embryonal stages. The growth factor stimulation was abolished by PKC
and tyrosine kinase inhibitors and was mimicked by
4-phorbol-12-myristate-13-acetate, dimethyl-2 (PMA). EGF treatment
did not modify the phosphorylation of the γ isoform of phospholipase C
(PLC-γ), and inositol trisphosphate (IP3) and intracellular calcium
levels, but it induced an increase in PKC activity. Our data show that
EGF regulates amino acid uptake, via PKC and without PLC-γ
activation, only in the last period of chick embryo hepatocyte
development. The effects of growth factor on PKC activity suggest the
involvement of PKC-α and -ε isoforms in EGF modulation of amino
acid transport.