Small Interfering RNA Library Screen of Human Kinases and Phosphatases
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Published OnlineFirst November 3, 2009; DOI: 10.1158/1535-7163.MCT-09-0365 3024 Small interfering RNA library screen of human kinases and phosphatases identifies polo-like kinase 1 as a promising new target for the treatment of pediatric rhabdomyosarcomas Kaiji Hu,1 Cathy Lee,1 Dexin Qiu,2 Abbas Fotovati,1 B1. Increased expression of WEE 1 was also noted. The Alastair Davies,1 Samah Abu-Ali,1 Daniel Wai,3 induction of apoptosis after PLK1 silencing was confirmed Elizabeth R. Lawlor,3 Timothy J. Triche,3 by increased p-H2AX, propidium iodide uptake, and chro- Catherine J. Pallen,2 and Sandra E. Dunn1 matin condensation, as well as caspase-3 and poly(ADP- ribose) polymerase cleavage. Pediatric Ewing's sarcoma 1Laboratory for Oncogenomic Research, Departments of (TC-32), neuroblastoma (IMR32 and KCNR), and glio- Pediatrics, Experimental Medicine, and Medical Genetics, and blastoma (SF188) models were also highly sensitive to 2 Cell Phosphosignaling Laboratory, Departments of Pediatrics, PLK1 inhibition. Finally, based on cDNA microarray anal- Pathology and Laboratory Medicine, and Experimental Medicine, Child and Family Research Institute, University of British yses, PLK1 mRNA was overexpressed (>1.5 fold) in 10 Columbia, Vancouver, British Columbia, Canada; and of 10 rhabdomyosarcoma cell lines and in 47% and 51% 3Department of Pathology, Keck School of Medicine of the of primary aRMS (17 of 36 samples) and eRMS (21 of 41 University of Southern California, Los Angeles, California samples) tumors, respectively, compared with normal muscles. Similarly, pediatric Ewing's sarcoma, neuro- Abstract blastoma, and osteosarcoma tumors expressed high PLK1.WeconcludethatPLK1couldbeapromisingther- Rhabdomyosarcoma, consisting of alveolar (aRMS) and apeutic target for the treatment of a wide range of pedi- embryonal (eRMS) subtypes, is the most common type atric solid tumors including rhabdomyosarcoma. [Mol of sarcoma in children. Currently, there are no targeted Cancer Ther 2009;8(11):3024–35] drug therapies available for rhabdomyosarcoma. In search- ing for new molecular therapeutic targets, we carried out genome-wide small interfering RNA (siRNA) library screens Introduction targeting human phosphatases (n = 206) and kinases (n = Rhabdomyosarcoma is the most common soft-tissue sarco- 691) initially against an aRMS cell line, RH30. Sixteen ma of children and adolescents. The majority (66%) of cases phosphatases and 50 kinases were identified based on of rhabdomyosarcoma are diagnosed in children <6 years of growth inhibition after 72 hours. Inhibiting polo-like kinase age (1). This disease is thought to arise from primitive mes- 1 (PLK1) had the most remarkable impact on growth inhi- enchymal progenitors that have undergone a limited pro- ∼ bition ( 80%) and apoptosis on all three rhabdomyosarco- gram of myogenic differentiation (2). Rhabdomyosarcoma ma cell lines tested, namely, RH30, CW9019 (aRMS), and consists of a highly heterogeneous family of tumors show- RD (eRMS), whereas there was no effect on normal muscle ing varying degrees of skeletal muscle differentiation (3). cells. The loss of PLK1 expression and subsequent growth Embryonal rhabdomyosarcoma (eRMS) and the morpho- inhibition correlated with decreased p-CDC25C and Cyclin logic spindle/botryoid variants are associated with interme- diate and superior patient prognosis, respectively, whereas alveolar rhabdomyosarcoma (aRMS) is more aggressive, Received 4/22/09; revised 8/7/09; accepted 9/4/09; published OnlineFirst with a high frequency of metastasis at the time of initial di- 11/3/09. agnosis (4). Current treatment for rhabdomyosarcoma in- Grant support: British Columbia Children's Hospital Pediatric Oncology cludes chemotherapy, radiation, and surgery. The “gold Collaborative Research Fund provided funding to support this project ” (S.E. Dunn and C.J. Pallen). The Michael Cuccione Foundation Research standard chemotherapeutic agents vincristine, actinomycin Fellowship also provided salary support (C. Lee). S.E. Dunn and C.J. Pallen D, and cyclophosphamide are commonly prescribed to are recipients of Investigator Awards from the Child and Family Research rhabdomyosarcoma patients (1). Chemoresistance is fairly Institute. Drs. Triche and Lawlor were supported by NIH SPECS grant 1U01CA11475-04. common as are treatment-related side effects (1, 5). This is The costs of publication of this article were defrayed in part by the coupled with the fact that the present cure rate for children payment of page charges. This article must therefore be hereby marked with metastatic rhabdomyosarcoma is still only 20% to 30% advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. (6, 7). Unlike advanced treatment strategies for other types Note: Supplementary materials for this article are available at Molecular of malignancies, there are no targeted drug therapies avail- Cancer Therapeutics Online (http://mct.aacrjournals.org/). able for rhabdomyosarcoma that could potentially improve Requests for reprints: Sandra E. Dunn, Departments of Pediatrics, overall cure rates and reduce morbidity. Thus, identifying Experimental Medicine, and Medical Genetics, Child and Family Research new molecular targets of the disease is necessary. Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, V5Z 4H4, Canada. Phone: 604-875-2000 ext. 6015; Loss of heterozygosity on the short arm of chromosome Fax: 604-875-3120. E-mail: [email protected] 11 (11p15.5) characterizes eRMS (8). In contrast, aRMS har- Copyright © 2009 American Association for Cancer Research. bors the reciprocal chromosomal translocations t(2;13)(q35; doi:10.1158/1535-7163.MCT-09-0365 q14) or t(1;13)(p36;q14), generating a chimeric fusion gene Mol Cancer Ther 2009;8(11). November 2009 Downloaded from mct.aacrjournals.org on September 27, 2021. © 2009 American Association for Cancer Research. Published OnlineFirst November 3, 2009; DOI: 10.1158/1535-7163.MCT-09-0365 Molecular Cancer Therapeutics 3025 involving the PAX 3 gene (chromosome 2) or PAX 7 (chro- plates. They were diluted to working stocks at 2 μmol/L mosome 1) and FKHR (chromosome 13), a member of the upon arrival following the manufacturer's instructions, fork-head family (9). The resulting gene fusions encode and were stored at −20°C until use. PAX3-FKHR and PAX 7- FK HR proteins that combine tran- siRNA Library Screen and High Content Screening scriptional domains from corresponding wild-type proteins Analysis and are more potent transcription factors (10). These pro- RH30 cells were seeded (5,000/well) into each well of 96- teins induce cell transformation and inhibit myogenic differ- well plates (Becton Dickinson) overnight. The cells were then entiation and apoptosis, thereby enhancing oncogenic transfected with siRNA using Lipofectamine RNAiMAX activity (11). Recently, several gene expression studies of (Invitrogen) following the manufacturer's instruction. The fi- primary rhabdomyosarcoma tumors have provided new nal concentration of siRNA was 5 nmol/L in 120 μL medium information about the pathways involved in rhabdomyosar- per well. The assay plates were incubated at 37°C with 5% – coma (6, 12 19). New evidence indicates that aRMS can be CO2 for 72h. Forty minutes before the end of siRNA treat- experimentally induced by expressing the PAX/FKHR ment, nuclear dyes, Hoechst 33342, and propidium iodide fusion gene in mesenchymal stem cells followed by the intro- (Sigma-Aldrich) were added to each well of the 96-well plates duction of activating RAS mutation (20). Despite new to give a final concentration of 1 μg/mL of each dye, and the knowledge and the belief that rhabdomyosarcoma arises plates were incubated as before. The cells were washed gent- from disrupted proliferation and differentiation of skeletal ly with PBS three times before the cells were fixed in 2% para- muscle progenitor cells, the mechanisms of growth control formaldehyde. The plates were kept at 4°C in the dark before of rhabdomyosarcoma are not fully understood. analysis on the ArrayScan HCS system (Thermo Fisher Scien- Kinases and phosphatases control the reversible processes tific). Twenty focus fields per cell well were scanned and an- of phosphorylation and are deregulated in many diseases, alyzed. The screen was repeated at least once to confirm the such as cancer. A recent study of genome-wide small interfer- activity of siRNAs. Cells treated with Lipofectamine RNAi- ing RNA (siRNA) libraries against the HeLa cervical carcino- MAX alone without siRNA served as controls. Additionally, ma cell line has shown that a variety of phosphatases and scrambled siRNAs and green fluorescent protein siRNAs kinases are critical in cancer cell survival (21). Kinase inhibi- were included in the libraries, and served as internal refer- tors targeting PAX3-FKHR, IGF-IR, CDK4/6, and EGFR have ences in each assay plate. Apoptosis was identified by nucle- also shown potent antitumorigenic activity on rhabdomyo- ar morphology and dye intensity by the ArrayScan HCS sarcoma under in vitro and in vivo conditions (5, 7, 22–24). It system (26). Growth inhibition was calculated as a percent- is reported that the phosphorylation levels of receptors and age of the control. To focus on the phosphatases and kinases nonreceptor tyrosine kinases, as well as protein kinase C, with the most significant effect on cell growth, only those are elevated in rhabdomyosarcoma tumors and therefore siRNAs that were active for both sequences and showed a have high therapeutic