Ubiquitin-mediated proteasomal degradation of non-synonymous SNP variants of human ABC transporter ABCG2.

Biochem J 2008 May;411(3):623-31

Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan.

Clinical relevance is implicated between the genetic polymorphisms of the ABC (ATP-binding cassette) transporter ABCG2 (ABC subfamily G, member 2) and the individual differences in drug response. We expressed a total of seven non-synonymous SNP (single nucleotide polymorphism) variants in Flp-In-293 cells by using the Flp (flippase) recombinase system. Of these, ABCG2 F208S and S441N variants were found to be expressed at markedly low levels, whereas their mRNA levels were equal to those of the other SNP variants and ABCG2 WT (wild-type). Interestingly, protein expression levels of the ABCG2 F208S and S441N variants increased 6- to 12-fold when Flp-In-293 cells were treated with MG132, a proteasome inhibitor. Immunoprecipitation followed by immunoblot analysis showed that the ABCG2 F208S and S441N variant proteins were endogenously ubiquitinated in Flp-In-293 cells, and treatment with MG132 significantly enhanced the level of these ubiquitinated variants. Immunofluorescence microscopy demonstrated that MG132 greatly affected the ABCG2 F208S and S441N variants in terms of both protein levels and intracellular distribution. Immunoblot analysis revealed that those variants were N-glycosylated; however, their oligosaccharides were immature compared with those present on ABCG2 WT. The ABCG2 F208S and S441N variant proteins do not appear to be processed in the Golgi apparatus, but undergo ubiquitin-mediated protein degradation in proteasomes, whereas ABCG2 WT is sorted to the plasma membrane and then degraded via the lysosomal pathway. The present study provides the first evidence that certain genetic polymorphisms can affect the protein stability of ABCG2. Control of proteasomal degradation of ABCG2 would provide a novel approach in cancer chemotherapy to circumvent multidrug resistance of human cancers.

Download full-text PDF

Source
http://biochemj.org/lookup/doi/10.1042/BJ20071229
Publisher Site
http://dx.doi.org/10.1042/BJ20071229DOI Listing
May 2008
4 Reads

Publication Analysis

Top Keywords

f208s s441n
20
abcg2 f208s
20
abcg2
12
s441n variants
12
flp-in-293 cells
12
snp variants
8
genetic polymorphisms
8
transporter abcg2
8
variants
8
variant proteins
8
s441n variant
8
non-synonymous snp
8
immunoblot analysis
8
proteasomal degradation
8
f208s
5
s441n
5
variants increased
4
processed golgi
4
increased 12-fold
4
golgi apparatus
4

References

(Supplied by CrossRef)
A human placenta-specific ATP-binding cassette gene (ABCP) on chromosome 4q22 that is involved in multidrug resistance
Allikmets et al.
Cancer Res. 1998
Molecular cloning of cDNAs which are highly overexpressed in mitoxantrone-resistant cells: demonstration of homology to ABC transport genes
Miyake et al.
Cancer Res. 1999
Identification of cysteine residues critically involved in homodimer formation and protein expression of human ATP-binding cassette transporter ABCG2: a new approach using the flp recombinase system
Wakabayashi et al.
J. Exp. Ther. Oncol. 2006
Overexpression of the BCRP/MXR/ABCP gene in a topotecan-selected ovarian tumor cell line
Maliepaard et al.
Cancer Res. 1999

Similar Publications