Major SNP (Q141K) variant of human ABC transporter ABCG2 undergoes lysosomal and proteasomal degradations.
OBJECTIVE
Single nucleotide polymorphisms (SNPs) of the ATP-binding cassette (ABC) transporter ABCG2 gene have been suggested to be a significant factor in patients' responses to medication and/or the risk of diseases. We aimed to evaluate the impact of the major non-synonymous SNP Q141K on lysosomal and proteasomal degradations.


METHODS
ABCG2 WT and the Q141K variant were expressed in Flp-In-293 cells by using the Flp recombinase system. Their expression levels and cellular localization was measured by immunoblotting and immunofluorescence microscopy, respectively.


RESULTS
The protein level of the Q141K variant expressed in Flp-In-293 cells was about half that of ABCG2 WT, while their mRNA levels were equal. The protein expression level of the Q141K variant increased about two-fold when Flp-In-293 cells were treated with MG132. In contrast, the protein level of ABCG2 WT was little affected by the same treatment. After treatment with bafilomycin A1, the protein levels of ABCG2 WT and Q141K increased 5- and 2-fold in Flp-In-293 cells, respectively.


CONCLUSIONS
The results strongly suggest that the major non-synonymous SNP Q141K affects the stability of the ABCG2 protein in the endoplasmic reticulum and enhances its susceptibility to ubiquitin-mediated proteasomal degradation.
Furukawa
Tomoka
T
Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-B-60 Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan.
Wakabayashi
Kanako
K
Tamura
Ai
A
Nakagawa
Hiroshi
H
Morishima
Yoshihiro
Y
Osawa
Yoichi
Y
Ishikawa
Toshihisa
T
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D006801:Humans; D015151:Immunoblotting; D000077146:Irinotecan; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology*; D018942:Macrolides / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D020641:Polymorphism, Single Nucleotide; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D055550:Protein Stability; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D025801:Ubiquitin / Q000378:metabolism
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000972:Antineoplastic Agents, Phytogenic; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D018942:Macrolides; D009363:Neoplasm Proteins; D061988:Proteasome Inhibitors; D012333:RNA, Messenger; D025801:Ubiquitin; D000077146:Irinotecan; C040929:bafilomycin A1; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D002166:Camptothecin