Role of Cys-603 in dimer/oligomer formation of the breast cancer resistance protein BCRP/ABCG2.

Breast cancer resistance protein (BCRP/ABCG2) is a half-molecule ATP-binding cassette transporter that we have previously suggested might function as a homodimer, bridged by disulfide bonds. In the present study, we carried out cysteine-scanning mutagenesis, substituting Ser for Cys, and established 12 PA317 transfectants expressing BCRP mutants with possible disruptions to their S-S bonds. Western blot analysis of BCRP from the wild-type transfectants (PA/WT) confirmed that the wild-type protein migrates as a 140-kDa dimer under non-reducing conditions, but as a 70-kDa monomer under reducing conditions.

C421A polymorphism in the human breast cancer resistance protein gene is associated with low expression of Q141K protein and low-level drug resistance.

Breast cancer resistance protein (BCRP) confers multidrug resistance to cancer cells against agents such as SN-38 (an active metabolite of irinotecan), mitoxantrone, and topotecan. Among 59 human tumor cell lines tested, 6 cell lines, A549, NCI-H460, KM-12, HT-29, OVCAR-5, and RPMI8226, showed high BCRP expression. BCRP cDNA was isolated from 11 cancer cell lines and three variant cDNAs [G34A substituting Met for Val-12 (V12M), C421A substituting Lys for Gln-141 (Q141K), and 944-949 deletion lacking Ala-315 and Thr-316 (delta315-6)] were identified.

Dominant-negative inhibition of breast cancer resistance protein as drug efflux pump through the inhibition of S-S dependent homodimerization.

Breast cancer resistance protein (BCRP) is a half-molecule ABC transporter highly expressed in mitoxantrone-resistant cells. In our study we established PA317 transfectants expressing Myc-tagged BCRP (MycBCRP) or HA-tagged BCRP (HABCRP). The exogenous BCRP protein migrated as a 70-kDa protein in SDS-PAGE under reducing condition, but migrated as a 140-kDa complex in the absence of reducing agents.