Vaj. Smits et al., Negative growth regulation of SK-N-MC cells by bFGF defines a growth factor-sensitive point in G(2), J BIOL CHEM, 275(25), 2000, pp. 19375-19381
Basic fibroblast growth factor (bFGF) has been shown to induce growth inhib
ition of the neuroepithelioma cell line SK-N-MC, Here we show that this gro
wth inhibition occurs in G(2). We show that bFGF is active on these cells d
uring S and early G(2) phase. Therefore, this constitutes a rather unusual
mechanism of growth inhibition, because it is generally believed that cells
become refractory to extracellular signals after passage through the restr
iction point. We show that bFGF treatment inhibits Tyr-15 dephosphorylation
of cdc2 and prevents activation of Cdc25C, similar to what is seen upon ac
tivation of the G(2) DNA damage checkpoint. Interestingly, both DNA damage-
and bFGF-induced effects on cdc2 phosphorylation are reverted by caffeine.
To confirm the involvement of similar pathways induced by bFGF and DNA dam
age, we generated tetracycline-regulatable SK-N-MC clones expressing Cdc25C
-S216A. Expression of this Cdc25C mutant can revert the bFGF-induced effect
s on cdc2 phosphorylation and can rescue cells from the block in G(2) impos
ed by bFGF. Taken together, these data define a growth factor-sensitive poi
nt in G(2) that most likely involves regulation of Cdc25C phosphorylation.