Overexpression of CIP2A is associated with poor prognosis in multiple myeloma

OPEN Citation: Signal Transduction and Targeted Therapy (2017) 2, 17013; doi:10.1038/sigtrans.2017.13 www.nature.com/sigtrans ARTICLE Overexpression of CIP2A is associated with poor prognosis in multiple myeloma Xuewen Liu1,6, Wei Cao2,6, Shanshan Qin1, Te Zhang1, Junnian Zheng3, Ying Dong4, Pinghong Ming5, Qian Cheng3, Zheng Lu3, Yang Guo1, Baofu Zhang3 and Ying Liu1 Cancerous inhibitor of protein phosphatase 2A (CIP2A), an endogenous protein phosphatase 2A (PP2A) inhibitor, has been identified as an oncoprotein in promoting cancer initiation and progression of several types of cancer. However, the expression and the role played by CIP2A in the pathogenesis of multiple myeloma (MM) remain unclear. In this study, we showed that CIP2A was overexpressed in human MM cell lines and MM patients’ bone marrow tissues. Clinicopathologic analysis showed that CIP2A expression was significantly correlated with clinical stage and percent of plasma cells in bone marrow. Kaplan–Meier analysis revealed that patients with high CIP2A expression presented with poorer overall survival rates than those with low CIP2A expression. Moreover, CIP2A knockdown in MM cells resulted in attenuated proliferative abilities. In addition, CIP2A depletion sensitizes dexamethasone (Dex)-resistant cells to Dex. The effect of CIP2A on proliferation and Dex therapy was mediated by the inhibition of PP2A, which in turn activated Akt. In vivo studies confirmed that CIP2A regulated MM tumorigenesis and the phosphorylation of Akt. Taken together, our results suggest that CIP2A oncoprotein plays an important role in MM progression and could serve as a prognosis marker and a novel therapeutic target for the treatment of patients with MM. Signal Transduction and Targeted Therapy (2017) 2, 17013; doi:10.1038/sigtrans.2017.13; published online 26 May 2017 INTRODUCTION As a neoplastic disorder of plasma cells characterized by clonal proliferation within the bone marrow (BM), multiple myeloma (MM) accounts for ~ 10% of all hematological cancers and ~ 1% of all cancer deaths.1 In 2017, the annual incidence of MM increased with the aging of the population worldwide. An estimated 30 280 new cases (17 490 in men and 12 790 in women) of MM were diagnosed in 2017, and 12 590 deaths (6660 in men and 5930 in women) are estimated to occur from this disease in the United States.2 Overall survival has improved in recent years. Patients are now predicted to have a median survival of ~ 5 years.3 Unfortunately, despite the improved therapeutic armamentarium, nearly all patients experience relapse and refractory disease. To date, MM remains an incurable disease. Therefore, there is an urgent need to explore novel therapeutic target and agent to improve the survival of patients with MM. The oncogenic transformation of human cells requires the perturbation of a distinct set of oncogenes and tumor suppressors. Protein phosphatase 2A (PP2A) complexes function as tumor suppressors by inhibiting the activity of several critical oncogenic signaling pathways such as Akt and ERK.4 Consequently, inhibition of PP2A phosphatase activity is one of many prerequisites for the transformation of normal human cells into cancerous cells. However, the mechanisms underlying PP2A inactivation in human cancers are poorly understood. Cancerous inhibitor of protein phosphatase 2A (CIP2A), a recently identified endogenous PP2A inhibitor in malignant cells, is one possible mechanism. CIP2A stabilizes c-Myc protein by inhibiting its degradation mediated by PP2A in cancer cells.5 In addition to inhibiting c-Myc degradation, CIP2A is regulated in a positive feedback loop with c-Myc by promoting each other’s expression.6 Previous independent studies showed that aberrant overexpression of CIP2A is associated with tumor growth, resistance to apoptosis, drug resistance, prognosis and metastasis in many human solid malignancies including head and neck,5 gastric,7 breast,8 tongue,9 ovarian,10 and lung cancers.11 Besides, CIP2A downregulation and inactivation of the Akt pathway have been reported to inhibit the proliferation and to induce apoptosis in a variety of hematologic neoplasms.12–14 Importantly, recent studies provided evidence that high CIP2A expression is a poor prognostic factor in normal karyotype acute myeloid leukemia (AML).12 Barragán et al.12 showed that high CIP2A expression is a recurrent event in AML, where it represents a marker of reduced overall survival and a poor prognostic factor, as previously reported in other tumors. In addition, CIP2A depletion downregulates cell proliferation. Thus, CIP2A represents a novel therapeutic target in AML. Furthermore, CIP2A is associated with radioresistance and modulates the sensitivity of breast cancer cells to bortezomib treatments.15 Choi et al.16 determined that CIP2A expression is associated with the sensitivity to doxorubicin and CIP2A overexpression in MCF-7 cells overcame the inhibition of cell proliferation in response to doxorubicin treatment. Moreover, CIP2A knockdown may sensitize metastatic castration-resistant prostate cancer cells to cabazitaxel chemotherapy.17 Liu and colleagues18 also showed that CIP2A knockdown increased the 1 Laboratory of Molecular Target Therapy of Cancer, Institute of Basic Medical Sciences; Hubei University of Medicine, Shiyan, China; 2MOE Key Laboratory of Industrial Fermentation Microbiology, College of Biotechnology, Tianjin University of Science and Technology, Tianjin, China; 3Jiangsu Center for the Collaboration and Innovation of Cancer Biotherapy, Cancer Institute, Xuzhou Medical University, Xuzhou, China; 4Department of Oncology, The Second Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China and 5Department of Pathology, Zhuhai Hospital Affiliated with Jinan University, Zhuhai, China. Correspondence: Y Liu () 6 These authors contributed equally to this work. Received 22 November 2016; revised 4 February 2017; accepted 2 March 2017 Overexpression of CIP2A X Liu et al 2 drug sensitivity of HeLa and doxorubicin-resistant HeLa cells. In addition, CIP2A is involved in regulating multidrug resistance of cervical adenocarcinoma upon chemotherapy by enhancing P-glycoprotein expression through E2F1. Conclusively, De and colleagues1 reviewed that CIP2A acts as an ‘oncogenic nexus’ contributing to cancer development, cancer evolution and drug resistance, suggesting that CIP2A can be targeted in cancer. However, the role of CIP2A in MM tumorigenesis and metastasis remains less elusive. Recently, Yang et al.19 determined that CIP2A silencing inhibited proliferation and promoted apoptosis in MM cell lines RPMI 8226 and NCI-H929 cells. In this study, we analyzed the expression of CIP2A in MM specimens and cell lines by real-time quantitative PCR, western blot and immunohistochemistry. We also measured the effect of CIP2A on MM cell proliferation and dexamethasone (Dex)mediated inhibition of cell proliferation in Dex-resistant cell lines. Our fin (...truncated)