title: Inhibition of mitogen-activated protein kinase Erk1/2 promotes protein degradation of ATP binding cassette transporters A1 and G1 in CHO and HuH7 cells.
abstract: Signal transduction modulates expression and activity of cholesterol transporters. We recently demonstrated that the Ras/mitogen-activated protein kinase (MAPK) signaling cascade regulates protein stability of Scavenger Receptor BI (SR-BI) through Proliferator Activator Receptor (PPARα) -dependent degradation pathways. In addition, MAPK (Mek/Erk 1/2) inhibition has been shown to influence liver X receptor (LXR) -inducible ATP Binding Cassette (ABC) transporter ABCA1 expression in macrophages. Here we investigated if Ras/MAPK signaling could alter expression and activity of ABCA1 and ABCG1 in steroidogenic and hepatic cell lines. We demonstrate that in Chinese Hamster Ovary (CHO) cells and human hepatic HuH7 cells, extracellular signal-regulated kinase 1/2 (Erk1/2) inhibition reduces PPARα-inducible ABCA1 protein levels, while ectopic expression of constitutively active H-Ras, K-Ras and MAPK/Erk kinase 1 (Mek1) increases ABCA1 protein expression, respectively. Furthermore, Mek1/2 inhibitors reduce ABCG1 protein levels in ABCG1 overexpressing CHO cells (CHO-ABCG1) and human embryonic kidney 293 (HEK293) cells treated with LXR agonist. This correlates with Mek1/2 inhibition reducing ABCG1 cell surface expression and decreasing cholesterol efflux onto High Density Lipoproteins (HDL). Real Time reverse transcriptase polymerase chain reaction (RT-PCR) and protein turnover studies reveal that Mek1/2 inhibitors do not target transcriptional regulation of ABCA1 and ABCG1, but promote ABCA1 and ABCG1 protein degradation in HuH7 and CHO cells, respectively. In line with published data from mouse macrophages, blocking Mek1/2 activity upregulates ABCA1 and ABCG1 protein levels in human THP1 macrophages, indicating opposite roles for the Ras/MAPK pathway in the regulation of ABC transporter activity in macrophages compared to steroidogenic and hepatic cell types. In summary, this study suggests that Ras/MAPK signaling modulates PPARα- and LXR-dependent protein degradation pathways in a cell-specific manner to regulate the expression levels of ABCA1 and ABCG1 transporters.
authors: Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia.
authors: Vishwaroop
authors: V
authors: Mulay
authors: Peta
authors: P
authors: Wood
authors: Melanie
authors: M
authors: Manetsch
authors: Masoud
authors: M
authors: Darabi
authors: Rose
authors: R
authors: Cairns
authors: Monira
authors: M
authors: Hoque
authors: Karen Cecilia
authors: KC
authors: Chan
authors: Meritxell
authors: M
authors: Reverter
authors: Anna
authors: A
authors: Alvarez-Guaita
authors: Kerry-Anne
authors: KA
authors: Rye
authors: Carles
authors: C
authors: Rentero
authors: Joerg
authors: J
authors: Heeren
authors: Carlos
authors: C
authors: Enrich
authors: Thomas
authors: T
authors: Grewal
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D016466:CHO Cells; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D055550:Protein Stability / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects*; D018631:ras Proteins / Q000378:metabolism
chemical_list: C419353:ABCG1 protein, human; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D047428:Protein Kinase Inhibitors; D002784:Cholesterol; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D018631:ras Proteins
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