Human splicing factor SPF45 (RBM17) confers broad multidrug resistance to anticancer drugs when overexpressed--a phenotype partially reversed by selective estrogen receptor modulators.
The splicing factor SPF45 (RBM17) is frequently overexpressed in many solid tumors, and stable expression in HeLa cells confers resistance to doxorubicin and vincristine. In this study, we characterized stable transfectants of A2780 ovarian carcinoma cells. In a 3-day cytotoxicity assay, human SPF45 overexpression conferred 3- to 21-fold resistance to carboplatin, vinorelbine, doxorubicin, etoposide, mitoxantrone, and vincristine. In addition, resistance to gemcitabine and pemetrexed was observed at the highest drug concentrations tested. Knockdown of SPF45 in parental A2780 cells using a hammerhead ribozyme sensitized A2780 cells to etoposide by approximately 5-fold relative to a catalytically inactive ribozyme control and untransfected cells, suggesting a role for SPF45 in intrinsic resistance to some drugs. A2780-SPF45 cells accumulated similar levels of doxorubicin as vector-transfected and parental A2780 cells, indicating that drug resistance is not due to differences in drug accumulation. Efforts to identify small molecules that could block SPF45-mediated drug resistance revealed that the selective estrogen receptor (ER) modulators tamoxifen and LY117018 (a raloxifene analogue) partially reversed SPF45-mediated drug resistance to mitoxantrone in A2780-SPF45 cells from 21-fold to 8- and 5-fold, respectively, but did not significantly affect the mitoxantrone sensitivity of vector control cells. Quantitative PCR showed that ERbeta but not ERalpha was expressed in A2780 transfectants. Coimmunoprecipitation experiments suggest that SPF45 and ERbeta physically interact in vivo. Thus, SPF45-mediated drug resistance in A2780 cells may result in part from effects of SPF45 on the transcription or alternate splicing of ERbeta-regulated genes.
Perry
William L
WL
Lilly Research Laboratories, Eli Lilly and Co., Indianapolis, Indiana 46285, USA. bperry@lilly.com
Shepard
Robert L
RL
Sampath
Janardhan
J
Yaden
Benjamin
B
Chin
William W
WW
Iversen
Philip W
PW
Jin
Shengfang
S
Lesoon
Andrea
A
O'Brien
Kathryn A
KA
Peek
Victoria L
VL
Rolfe
Mark
M
Shyjan
Andrew
A
Tighe
Michelle
M
Williamson
Mark
M
Krishnan
Venkatesh
V
Moore
Robert E
RE
Dantzig
Anne H
AH
D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000493:pharmacokinetics / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000187:drug effects / Q000502:physiology*; D019008:Drug Resistance, Neoplasm; D047629:Estrogen Receptor beta / Q000378:metabolism; D005047:Etoposide / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D006801:Humans; D008942:Mitoxantrone / Q000493:pharmacokinetics / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D016337:RNA, Catalytic / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*; D013629:Tamoxifen / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D014162:Transfection
D000970:Antineoplastic Agents; D047629:Estrogen Receptor beta; D011759:Pyrrolidines; C121693:RBM17 protein, human; D000072260:RNA Splicing Factors; D016337:RNA, Catalytic; D016601:RNA-Binding Proteins; D020845:Selective Estrogen Receptor Modulators; D013876:Thiophenes; D013629:Tamoxifen; C025430:LY 117018; D005047:Etoposide; D004317:Doxorubicin; D008942:Mitoxantrone