Increased nuclear localization of transcription factor Y-box binding protein 1 accompanied by up-regulation of P-glycoprotein in breast cancer pretreated with paclitaxel.
OBJECTIVE
The Y-box binding protein 1 (YB-1) regulates expression of P-glycoprotein encoded by the MDR1 gene. There have been no previous studies regarding the involvement of YB-1 in the development of resistance to paclitaxel. The present study was done to examine how paclitaxel affects the localization and expression of YB-1 in breast cancer.


METHODS
We evaluated the expression and localization of YB-1 and P-glycoprotein in breast cancer tissues obtained from 27 patients before and after treatment with paclitaxel. The effect of paclitaxel on localization of cellular YB-1 was examined by using GFP-YB-1. Interaction of YB-1 with the Y-box motif of the MDR1 promoters was studied by electrophoretic mobility shift assay. The effects of paclitaxel on MDR1 promoter activity were examined by luciferase assay.


RESULTS
Of 27 breast cancer tissues treated with paclitaxel, nine (33%) showed translocation of YB-1 from the cytoplasm to the nucleus together with increased expression of P-glycoprotein during the course of treatment. Twelve breast cancer tissues (44%) showed neither translocation of YB-1 nor increased expression of P-glycoprotein. Nuclear translocation of YB-1 was correlated significantly with increased expression of P-glycoprotein (P=0.0037). Confocal analysis indicated that paclitaxel induced nuclear translocation of green fluorescent fused YB-1 in MCF7 cells. Furthermore, binding of YB-1 to the Y-box of MDR1 promoter was increased in response to treatment with paclitaxel. In addition, MDR1 promoter activity was significantly up-regulated by paclitaxel in MCF7 cells (P<0.001).


CONCLUSIONS
The results of the present study suggested that YB-1 may be involved in the development of resistance to paclitaxel in breast cancer.
Fujita
Tomoyuki
T
Department of Surgery, Shinshu University School of Medicine, Matsumoto, Nagano, and Department of Surgery, Niigata Cancer Center Hospital, Japan.
Ito
Ken-ichi
K
Izumi
Hiroto
H
Kimura
Morihiko
M
Sano
Muneaki
M
Nakagomi
Hiroshi
H
Maeno
Kazuma
K
Hama
Yoshihisa
Y
Shingu
Kiyoshi
K
Tsuchiya
Shin-ichi
S
Kohno
Kimitoshi
K
Fujimori
Minoru
M
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy* / Q000378:metabolism; D002467:Cell Nucleus / Q000737:chemistry* / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D017239:Paclitaxel / Q000494:pharmacology / Q000627:therapeutic use*; D011401:Promoter Regions, Genetic; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D051840:Y-Box-Binding Protein 1 / Q000032:analysis* / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D051840:Y-Box-Binding Protein 1; D017239:Paclitaxel