Hormone-dependent beta-casein mRNA stabilization requires ongoing protein synthesis.
The role of ongoing protein synthesis in mediating the posttranscriptional effects of hormones on casein gene expression in the COMMA D mouse mammary epithelial cell line was investigated using the protein synthesis inhibitors, cycloheximide and anisomycin. When COMMA D cells were pretreated with insulin and PRL for 24 h, the addition of glucocorticoids induced a greater than 20-fold increase in beta-casein mRNA accumulation with an apparent lag of greater than 8 h. Addition of cycloheximide and anisomycin not only prevented this increase, but unexpectedly, resulted in the rapid disappearance of preexisting beta-casein mRNA with a half-life of approximately 2 h. Under the same conditions, the levels of beta-actin and histone H4 mRNAs were increased markedly. In contrast, when cells were pretreated with all three lactogenic hormones for 48 h before the addition of either protein synthesis inhibitors or actinomycin D, the effects of these inhibitors on the levels of beta-casein mRNA were greatly diminished. This differential sensitivity of beta-casein mRNA to protein synthesis inhibitors was observed only in cells pretreated for greater than 24 h with all three hormones. Experiments performed in the absence of inhibitors indicated that beta-casein mRNA has a long half-life even after hormone withdrawal. These results suggest that hormone-dependent stabilization of cytoplasmic beta-casein mRNA requires ongoing protein synthesis. Cells cultured in the presence of all three lactogenic hormones slowly accumulate a labile protein(s), which exerts a selective effect on casein mRNA stability.
Poyet
P
P
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030-3498.
Henning
S J
SJ
Rosen
J M
JM
D000199:Actins / Q000235:genetics; D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D002364:Caseins / Q000235:genetics*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D006657:Histones / Q000235:genetics; D008321:Mammary Glands, Animal / Q000378:metabolism*; D051379:Mice; D011388:Prolactin / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism*
D000199:Actins; D002364:Caseins; D005938:Glucocorticoids; D006657:Histones; D012333:RNA, Messenger; D000841:Anisomycin; D011388:Prolactin; D003513:Cycloheximide