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J. Biol. Chem., Vol. 261, Issue 2, 723-727, 01, 1986
Lack of association of epidermal growth factor-, insulin-, and serum- induced mitogenesis with stimulation of phosphoinositide degradation in BALB/c 3T3 fibroblasts
JM Besterman, SP Watson and P Cuatrecasas
The hypothesis that inositol phospholipid degradation is a step in the
mechanism by which epidermal growth factor (EGF) stimulates mitogenesis in
confluent monolayers of quiescent BALB/c 3T3 fibroblasts was tested. The
maximum mitogenic response (a nearly 30-fold increase in incorporation of
[3H]thymidine) occurred at 1 ng/ml EGF (0.16 nM). This degree of
stimulation corresponded to 60% of that elicited by 10% serum. To determine
whether EGF stimulated formation of inositol phosphates via degradation of
polyphosphoinositides, the intracellular levels of [3H] inositol phosphates
and [3H]phosphoinositides were determined after EGF addition to BALB/c 3T3
fibroblasts prelabeled with [3H]inositol. These experiments were performed
under conditions designed to mimic exactly those conditions used to study
mitogenesis. The results demonstrated that 10% serum or 10 ng/ml of
platelet-derived growth factor, but not as much as 50 ng/ml EGF or 10
micrograms/ml insulin, increased the levels of inositol phosphates via
degradation of phosphoinositides in the presence of 10 mM Li+. The
serum-induced effects occurred in 30 s, the earliest time investigated.
Phorbol dibutyrate (100 nM), alone or in conjunction with EGF (10 ng/ml),
failed to stimulate inositol phospholipid degradation. However, phorbol
dibutyrate inhibited the serum-induced stimulation. Finally, fetal bovine
serum dialyzed so as to retain peptide mitogens lost almost 70% of the
capacity to stimulate degradation of inositol phospholipids while remaining
as mitogenic as the control serum. Thus, stimulation of inositol
phospholipid degradation is an unlikely component in the mechanism by which
EGF and probably insulin and serum stimulate mitogenesis in BALB/c 3T3
fibroblasts.

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Copyright © 1986 by the American Society for Biochemistry and Molecular Biology.
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