Epidermal growth factor increases the level of the cyclin-dependent kinase(CDK) inhibitor p21/CIP1 (CDK-interacting protein 1) in A431 cells by increasing the half-lives of the p21/CIP1 transcript and the p21/CIP1 protein
Le. Johannessen et al., Epidermal growth factor increases the level of the cyclin-dependent kinase(CDK) inhibitor p21/CIP1 (CDK-interacting protein 1) in A431 cells by increasing the half-lives of the p21/CIP1 transcript and the p21/CIP1 protein, BIOCHEM J, 337, 1999, pp. 599-606
DNA synthesis was inhibited in A431 cells by epidermal growth factor (EGF)
in a p21/CIP1-dependent manner [where CIP1 is cyclin-dependent kinase (CDK)
-interacting protein 1]. When 1 or 10 nM EGF was added, the level of p21/CI
P1 was increased to the same extent, and the protein level peaked after app
rox. 5 h of incubation. The increase in p21/CIP1 mRNA upon addition of EGF
was rapid, and was enhanced in the presence of cycloheximide. The half-life
of p21/CIP1 mRNA in EGF-treated A431 cells was increased approx. 2-fold; t
his is in contrast with the case in MCF-7 cells with normal p53, in which t
he half-life of p21/CIP1 mRNA was not increased upon addition of EGF. This
increased stability accounts for most of the increase in mRNA levels observ
ed in A431 cells during short incubation periods. Additionally, upon prolon
ged incubation of A431 cells with EGF, the half-life of the protein was als
o increased compared with that in untreated cells and in cells treated with
EGF for short time periods. Nuclear run-on assays demonstrated only margin
al stimulation of transcription by 10 or 1 nM EGF, or by 10 ng/ml tumour ne
crosis factor alpha. Our results indicate that the most important mechanism
s by which EGF increases p21/CIP1 protein levels in A431 cells are post-tra
nscriptional and posttranslational stabilization.