title: Insulin-like growth factor I enhances the expression of aromatase P450 by inhibiting autophagy.
abstract: Aromatase, a key enzyme of estrogen biosynthesis, is transcriptionally regulated by many growth factors. IGF-I enhances aromatase activity in a variety of cells, but the mechanism of action has not been determined. We herein report our finding of a novel mechanism of action for IGF-I. IGF-I enhanced the dexamethasone (DEX)-induced aromatase activity by 30% in serum-starved THP-1 cells. The increase was associated with a corresponding increase in the level of aromatase protein but not with any change in the mRNA level. Metabolic labeling experiments revealed that IGF-I inhibited the degradation of aromatase. We identified pepstatin A as the most effective inhibitor of aromatase degradation by in vitro assay. Using a nontoxic concentration of pepstatin A, we examined IGF-I's action on aromatase distribution in microsomes and lysosomes. In the presence of pepstatin A, DEX caused an increase in the amount of aromatase in both microsomes and lysosomes, and IGF-I attenuated the DEX-induced accumulation of aromatase in lysosomes and, conversely, enhanced its accumulation in the microsomes. The addition of serum abolished the IGF-I-induced changes. The transport from microsome to lysosome was fluorescently traced in cells using a recombinant aromatase. IGF-I selectively reduced the aromatase signal in the lysosomes. Finally, we observed that IGF-I enhanced the aromatase activity by 50% as early as 1 h after treatment; furthermore, rapamycin, an enhancer of autophagy, completely negated the effect of IGF-I on the enzyme. These results indicate that IGF-I enhances aromatase by the inhibition of autophagy.
authors.affiliation: Department of Obstetrics and Gynecology, Kanazawa University Graduate School of Medicine, Kanazawa 920-0934, Japan.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Makio
authors.initials: M
authors.lastname: Shozu
authors.forename: Masahiko
authors.initials: M
authors.lastname: Okada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Tadayuki
authors.initials: T
authors.lastname: Kasai
authors.forename: Kouich
authors.initials: K
authors.lastname: Murakami
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Nomura
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Harada
authors.forename: Masaki
authors.initials: M
authors.lastname: Inoue
mesh_terms: D001141:Aromatase / Q000235:genetics* / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D010436:Pepstatins / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D010436:Pepstatins; D011480:Protease Inhibitors; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D001141:Aromatase; C031375:pepstatin