Abstract
Epidermal growth factor (EGF) is a multifunctional growth factor known to play a major role in proliferation and differentiation processes. EGF-induced differentiation is a prerequisite for function of various cell types, among them cytotrophoblasts, a functionally important cellular fraction in human placenta. Stimulation of cytotrophoblasts with EGF results in formation of a multinuclear syncytium representing the feto-maternal interface, which protects the fetus against exogenous substances. It is well established that part of this protection system is based on ATP-binding cassette (ABC) transporters such as ABCG2 (breast cancer resistance protein, BCRP). However, little is known about regulation of transport proteins in the framework of EGF-mediated cellular differentiation. In the present work we show a significant increase of ABCG2 expression by EGF in cytotrophoblasts, BeWo, and MCF-7 cells on both mRNA and protein levels. This increase resulted in decreased sensitivity to the ABCG2 substrates mitoxantrone and topotecan. In each cell type, EGF increases expression of ABCG2 by activation of mitogen-activated protein kinase cascade via phosphorylation of extracellular regulated kinase (ERK)1/2 and c-jun NH-terminal kinase/stress-activated protein kinase (JNK/SAPK). Consequently, the increase of ABCG2 by EGF was abolished by pretreatment of cells with the tyrosine kinase inhibitor 4-(3-chloroanillino)-6,7-dimethoxyquinazoline (AG1478) or the mitogen-activated protein kinase kinase inhibitor 2′-amino-3′methoxyflavone (PD 98059), thereby reestablishing sensitivity toward mitoxantrone. Moreover, analysis of ABCG2 expression during placental development revealed a significant increase in preterm versus term placenta. Taken together, our data show regulation of ABCG2 expression by EGF. In view of EGF signal transduction as a target for drugs (e.g., gefitinib), which are in turn substrates and/or inhibitors of ABCG2, this regulation has therapeutic consequences.
Footnotes
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The present work was supported by a grant from Deutsche Forschungsgemeinschaft, Sonderforschungsbereich/Transregio 19-04; and from the Karl & Lore Klein Stiftung, Oy-Mittelberg, Germany.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.105.007591.
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ABBREVIATIONS: EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; TKI, tyrosine kinase inhibitor; AP-1, activation protein-1; MEM, modified Eagle's medium; FCS, fetal calf serum; MAPK, mitogen-activated kinase; ERK1/2, extracellular regulated kinase; pERK1/2, phosphorylated extracellular regulated kinase; JNK/SAPK, c-jun NH-terminal kinase/stress-activated protein kinase; pJNK/SAPK, phosphorylated c-jun NH-terminal kinase/stress-activated protein kinase; PCR, polymerase chain reaction; BSA, bovine serum albumin; β-hCG, β-human choriogonadotropin; PD, PD 98059: 2′-amino-3′methoxyflavone; AG, AG1478: 4-(3-chloroanillino)-6,7-dimethoxyquinazoline; ABC, ATP-binding cassette; MEK, mitogen-activated protein kinase kinase; BCRP, breast cancer resistance protein; PBS, phosphate-buffered saline; PAGE, polyacrylamide gel electrophoresis; TBST, Tris-buffered saline (0.5 M Tris, 1.5 M NaCl) supplemented with 0.1% Tween; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid; ANOVA, analysis of variance.
- Received September 25, 2005.
- Accepted January 4, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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