RT Journal Article
SR Electronic
T1 Evidence for the Involvement of Protein Kinase C in the Inhibition of Prolactin Gene Expression by Transforming Growth Factor<strong>-</strong>β<sub>2</sub>
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1054
OP 1061
VO 53
IS 6
A1 Chuan-Chang Chuang
A1 Sai-Koong Tan
A1 Lung-Kuo Tai
A1 Jin-Ping Hsin
A1 Fung-Fang Wang
YR 1998
UL http://molpharm.aspetjournals.org/content/53/6/1054.abstract
AB We investigated the mechanisms by which transforming growth factor (TGF)-β2 inhibited prolactin mRNA expression in GH3 rat pituitary tumor cells. Maximal inhibition was observed with cells exposed to 5 ng/ml TGF-β2 for 24 hr. Continuous presence of the hormone during the entire period was not necessary because exposure of cells to TGF-β2 for 20 min was sufficient to trigger the same extent of prolactin mRNA inhibition at 24 hr as with its persistent presence. The action of TGF-β2 could be abolished by cycloheximide or EGTA, suggesting the requirement of a newly synthesized protein and extracellular Ca2+. The response of prolactin mRNA to TGF-β2 was inhibited by preincubation of cells with phorbol-12-myristate-13-acetate, which down-regulated protein kinase C (PKC). The activities of both the cytosolic and membrane PKC were significantly reduced at 20 min after TGF-β2 addition, and inhibition continued to 24 hr, the last time point analyzed. However, the ratio of cytosolic to membrane PKC was not altered by TGF-β2. Inhibition of PKC did not require the sustained presence of TGF-β2. In vitro kinase assays of the immunoprecipitated PKC demonstrated that the activities of α, ε, μ, and ζ isozymes were significantly decreased in the TGF-β2-treated cells, whereas that of PKCλ was not affected. Western blotting did not reveal any change in PKCε steady state protein levels, suggesting TGF-β2 inhibits PKC activity through a post-translational mechanism. Our results support that inhibition of PKC activity is an early event mediating TGF-β2-inhibited prolactin mRNA expression in GH3 cells. The American Society for Pharmacology and Experimental Therapeutics