A role for Akt in mediating the estrogenic functions of epidermal growth factor and insulin-like growth factor I.
This study examines whether the serine/threonine protein kinase, Akt, is involved in the cross-talk between epidermal growth factor (EGF) and insulin-related growth factor I (IGF-I) receptors and ER-alpha. Treatment of MCF-7 cells with either EGF or IGF-I resulted in a rapid phosphorylation of Akt and a 14- to 16-fold increase in Akt activity, respectively. Akt activation was blocked by inhibitors of phosphatidylinositol 3-kinase, but not by an inhibitor of the ribosomal protein kinase p70S6K. Stable transfection of cells with a dominant negative Akt mutant blocked the effects of EGF and IGF-I on ER-alpha expression and activity, whereas stable transfection of cells with a constitutively active Akt mutant mimicked the effects of EGF and IGF-I. In the latter cells, there was a decrease in the amount of ER-alpha protein and messenger RNA (70-80%) and an increase in the amount of progesterone receptor protein, messenger RNA (4- to 9- and by 3.5- to 7-fold, respectively) and pS2 (3- to 5-fold). Coexpression of wild-type ER-alpha and the dominant negative Akt mutant in COS-1 cells also blocked the growth factor-stimulated activation of ER-alpha, but coexpression of the wild-type receptor with the constitutively active Akt mutant increased ER-alpha activity. Receptor activation was blocked by an antiestrogen. Studies using mutants of ER-alpha demonstrated that Akt increased estrogen receptor activity through the amino-terminal activation function-1 (AF-1). Serines S104 S106, S118, and S167 appear to play a role in the activation of ER-alpha by Akt.
Martin
M B
MB
Department of Oncology, Lombardi Cancer Center, Georgetown University, Washington, DC 20007, USA.
Franke
T F
TF
Stoica
G E
GE
Chambon
P
P
Katzenellenbogen
B S
BS
Stoica
B A
BA
McLemore
M S
MS
Olivo
S E
SE
Stoica
A
A
D000818:Animals; D019556:COS Cells; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology / Q000502:physiology*; D047628:Estrogen Receptor alpha; D004967:Estrogens / Q000502:physiology*; D015870:Gene Expression; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D009154:Mutation; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000032:analysis; D011960:Receptors, Estrogen / Q000235:genetics / Q000502:physiology*; D011980:Receptors, Progesterone / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D047628:Estrogen Receptor alpha; D004967:Estrogens; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt