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Mol. Cell. Biol., Mar 1996, 762-770, Vol 16, No. 3
M Gorospe, Y Liu, Q Xu, FJ Chrest and NJ Holbrook
Prostaglandin A2 (PGA2) potently inhibits cell proliferation and suppresses
tumor growth in vivo, but little is known regarding the molecular
mechanisms mediating these effects. Here we demonstrate that treatment of
breast carcinoma MCF-7 cells with PGA2 leads to G1 arrest associated with a
dramatic decrease in the levels of cyclin D1 and cyclin-dependent kinase 4
(cdk4) and accompanied by an increase in the expression of p21. We further
show that these effects occur independent of cellular p53 status. The
decline in cyclin D and cdk4 protein levels is correlated with loss in cdk4
kinase activity, cdk2 activity is also significantly inhibited in
PGA2-treated cells, an effect closely associated with the upregulation of
p21. Immunoprecipitation experiments verified that p21 was indeed complexed
with cdk2 in PGA2- treated cells. Additional experiments with synchronized
MCF-7 cultures stimulated with serum revealed that treatment with PGA2
prevents the progression of cells from G1 to S. Accordingly, the kinase
activity associated with cdk4, cyclin E, and cdk2 immunocomplexes, which
normally increases following serum addition, was unchanged in PGA2- treated
cells. Furthermore, the retinoblastoma protein (Rb), a substrate of cdk4
and cdk2 whose phosphorylation is necessary for cell cycle progression,
remains underphosphorylated in PGA2-treated serum- stimulated cells. These
findings indicate that PGA2 exerts its growth- inhibitory effects through
modulation of the expression and/or activity of several key G1 regulatory
proteins. Our results highlight the chemotherapeutic potential of PGA2,
particularly for suppressing growth of tumors lacking p53 function.
Copyright © 1996, American Society for Microbiology
Inhibition of G1 cyclin-dependent kinase activity during growth arrest of human breast carcinoma cells by prostaglandin A2
Gerontology Research Center, National Institute on Aging, Baltimore, Maryland, USA.
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