Insulin and prolactin synergistically stimulate beta-casein messenger ribonucleic acid translation by cytoplasmic polyadenylation

Mol Endocrinol. 2004 Jul;18(7):1670-86. doi: 10.1210/me.2003-0483. Epub 2004 Apr 7.


Previous studies have shown that the synthesis and stability of milk protein mRNAs are regulated by lactogenic hormones. We demonstrate here in cultured mouse mammary epithelial cells (CID 9) that insulin plus prolactin also synergistically increases the rate of milk protein mRNA translation. Insulin alone stimulates synthesis of both milk and nonmilk proteins, whereas prolactin alone has no effect, but insulin plus prolactin selectively stimulate synthesis of milk proteins more than insulin alone. The increase in beta-casein mRNA translation is also reflected in a shift to larger polysomes, indicating an effect on translational initiation. Inhibitors of the phosphatidylinositol 3-kinase, mammalian target of rapamycin, and MAPK pathways block insulin-stimulated total protein and beta-casein synthesis but not the synergistic stimulation. Conversely, cordycepin abolishes synergistic stimulation of protein synthesis without affecting insulin-stimulated translation. The poly(A) tract of beta-casein mRNA progressively increases from approximately 20 to about 200 A residues over 30 min of treatment with insulin plus prolactin. The 3'-untranslated region of beta-casein mRNA containing an unaltered cytoplasmic polyadenylation element is sufficient for the translational enhancement and mRNA-specific polyadenylation, based on transient transfection of cells with a reporter construct. Insulin and prolactin stimulate cytoplasmic polyadenylation element binding protein phosphorylation with no increase of cytoplasmic poly(A) polymerase activity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3' Untranslated Regions
  • Adaptor Proteins, Signal Transducing
  • Animals
  • Carrier Proteins / drug effects
  • Carrier Proteins / metabolism
  • Caseins / drug effects
  • Caseins / genetics*
  • Caseins / metabolism
  • Cell Cycle Proteins
  • Cells, Cultured
  • Cytoplasm / drug effects
  • Cytoplasm / genetics*
  • Cytoplasm / metabolism
  • DNA-Directed DNA Polymerase / drug effects
  • DNA-Directed DNA Polymerase / metabolism
  • Drug Synergism
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism
  • Eukaryotic Initiation Factors
  • Female
  • Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / drug effects
  • Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / genetics
  • Insulin / metabolism
  • Insulin / pharmacology*
  • Mammary Glands, Animal / cytology
  • Mammary Glands, Animal / drug effects
  • Mice
  • Milk Proteins / biosynthesis
  • Milk Proteins / drug effects
  • Phosphoproteins / drug effects
  • Phosphoproteins / metabolism
  • Polyadenylation
  • Polyribosomes / metabolism
  • Prolactin / metabolism
  • Prolactin / pharmacology*
  • Protein Biosynthesis / drug effects*
  • RNA, Messenger / drug effects
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / drug effects
  • RNA-Binding Proteins / metabolism
  • Signal Transduction


  • 3' Untranslated Regions
  • Adaptor Proteins, Signal Transducing
  • CPEB protein, mouse
  • Carrier Proteins
  • Caseins
  • Cell Cycle Proteins
  • Eif4ebp1 protein, mouse
  • Eukaryotic Initiation Factors
  • Insulin
  • Milk Proteins
  • Phosphoproteins
  • RNA, Messenger
  • RNA-Binding Proteins
  • Prolactin
  • Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+)
  • DNA-Directed DNA Polymerase