CIP2A is overexpressed in osteosarcoma and regulates cell proliferation and invasion

CIP2A interacts with AKT1 to promote the malignant biological behaviors of oral squamous cell carcinoma by upregulating the GSK‑3β/β‑catenin pathway

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies worldwide, which is associated with a poor prognosis. The present study aimed to investigate the role of cancerous inhibitor of protein phosphatase 2A (CIP2A) in OSCC and its regulatory effect on AKT1. Firstly, CIP2A and AKT1 expression in OSCC cells was detected by western blotting. After silencing CIP2A, cell viability and cell proliferation were assessed using the Cell Counting Kit-8 assay and 5-ethynyl-2'-deoxyuridine staining. Cell apoptosis was evaluated by TUNEL staining and the expression of apoptosis-related proteins was assessed using western blotting. Wound healing, Transwell and tube formation assays were performed to evaluate CAL-27 cell migration, invasion and human umbilical vein endothelial cell (HUVEC) tube formation. The interaction between CIP2A and AKT1 was identified by co-immunoprecipitation (co-IP). In addition, AKT1 was overexpressed in CIP2A-silenced CAL-27 cells to perform rescue experiments to analyze the malignant biological functions of CAL-27 cells. Finally, the expression of proteins in the glycogen synthase kinase (GSK)-3β/β-catenin pathway was determined by western blot analysis. Markedly elevated CIP2A and AKT1 expression was observed in OSCC cells. CIP2A knockdown inhibited the viability, proliferation, migration and invasion, and promoted the apoptosis of CAL-27 cells. Concurrently, CIP2A loss-of-function attenuated tube formation. Results of Co-IP confirmed there was an interaction between CIP2A and AKT1. Rescue experiments suggested that AKT1 overexpression alleviated the inhibitory effects of CIP2A knockdown on the viability, proliferation, migration and invasion of CAL-27 cells, as well as tube formation in HUVECs . Additionally, CIP2A silencing significantly downregulated phosphorylated-GSK-3β and β-catenin expression, which was reversed by AKT1 overexpression. In conclusion, CIP2A could interact with AKT1 to promote the malignant biological behaviors of OSCC cells by upregulating the GSK-3β/β-catenin pathway. These findings may provide a targeted therapy for OSCC treatment.

From Basic Science to Clinical Practice: The Role of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A)/p90 in Cancer

Cancerous inhibitor of protein phosphatase 2A (CIP2A), initially reported as a tumor-associated antigen (known as p90), is highly expressed in most solid and hematological tumors. The interaction of CIP2A/p90, protein phosphatase 2A (PP2A), and c-Myc can hinder the function of PP2A toward c-Myc S62 induction, thus stabilizing c-Myc protein, which represents a potential role of CIP2A/p90 in tumorigeneses such as cell proliferation, invasion, and migration, as well as cancer drug resistance. The signaling pathways and regulation networks of CIP2A/p90 are complex and not yet fully understood. Many previous studies have also demonstrated that CIP2A/p90 can be used as a potential therapeutic cancer target. In addition, the autoantibody against CIP2A/p90 in sera may be used as a promising biomarker in the diagnosis of certain types of cancer. In this Review, we focus on recent advances relating to CIP2A/p90 and their implications for future research.

Cip2A modulates osteogenic differentiation via the ERK-Runx2 pathway in MG63 cells

Cancerous inhibitor of protein phosphatase 2A (Cip2A) is an oncoprotein that promotes the development of several types of cancer. However, its molecular function in osteoblast differentiation remains unclear. In this study, we found that Cip2A was upregulated under osteogenic conditions in MG63 cells. Besides, overexpression of Cip2A significantly increased the expression of Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). Inversely, the knockdown of Cip2A in MG63 cells suppressed osteoblast differentiation. Cip2A expression during osteogenic differentiation was mediated by extracellular signal-regulated kinase (ERK) activation. Taken together, our results suggest that Cip2A plays important role in regulating osteoblast differentiation by inducing ERK phosphorylation in MG63 cells.

Alantolactone suppresses human osteosarcoma through the PI3K/AKT signaling pathway

Osteosarcoma is the most common type of malignant bone cancer and results in cancer-related deaths among adolescents. Alantolactone (ALT) demonstrates antitumor properties in various diseases; however, its potential role in osteosarcoma is relatively unclear. The aim of the present study was to evaluate the effect of ALT on osteosarcoma. ALT significantly decreased the viability of U2OS and HOS osteosarcoma cell lines. Cells flow cytometry assay and Hoechst 33258 staining assay revealed that ALT significantly increased the proportion of apoptotic U2OS cells. In addition, wound healing and Transwell invasion assays demonstrated that the invasion and migration of osteosarcoma were markedly reduced upon ALT treatment. It was hypothesized that the antitumor functions of ALT are mediated through inhibition of the PI3K/AKT signaling pathway. In conclusion, the results of the present study confirmed the inhibition of ALT on osteosarcoma cells via downregulation of PI3K/AKT signaling pathways, suggesting ALT as a potential therapeutic candidate for osteosarcoma.

Chronic Cigarette Smoke Exposure Subdues PP2A Activity by Enhancing Expression of the Oncogene CIP2A

Phosphatase activity of the major serine threonine phosphatase, protein phosphatase 2A (PP2A), is blunted in the airways of individuals with chronic obstructive pulmonary disease (COPD), which results in heightened inflammation and proteolytic responses. The objective of this study was to investigate how PP2A activity is modulated in COPD airways. PP2A activity and endogenous inhibitors of PP2A were investigated in animal and cell models of COPD. In primary human bronchial epithelial (HBE) cells isolated from smokers and donors with COPD, we observed enhanced expression of cancerous inhibitor of PP2A (CIP2A), an oncoprotein encoded by the KIAA1524 gene, compared with cells from nonsmokers. CIP2A expression was induced by chronic cigarette smoke exposure in mice that coincided with a reduction in PP2A activity, airspace enlargements, and loss of lung function, as determined by PP2A phosphatase activity, mean linear intercept analysis, and forced expiratory volume in 0.05 second/forced vital capacity. Modulating CIP2A expression in HBE cells by silencing RNA or chemically with erlotinib enhanced PP2A activity, reduced extracellular-signal-regulated kinase phosphorylation, and reduced the responses of matrix metalloproteinases 1 and 9 in HBE cells isolated from subjects with COPD. Enhanced epithelial growth factor receptor responses in cells from subjects with COPD were observed to modulate CIP2A expression levels. Our study indicates that chronic cigarette smoke induction of epithelial growth factor receptor signaling and CIP2A expression can impair PP2A responses that are associated with loss of lung function and enhancement of proteolytic responses. Augmenting PP2A activity by manipulating CIP2A expression may represent a feasible therapeutic approach to counter smoke-induced lung disease.

β-Escin inhibits the proliferation of osteosarcoma cells via blocking the PI3K/Akt pathway

β-Escin exhibits anticancer effects on a panel of established cancer cells. However, the effects of β-escin on human osteosarcoma (OS) are still unknown. The aim of the present study was to investigate whether β-escin was effective against OS both in vivo and in vitro. Our results showed that β-escin induced dose- and time-dependent effects against MG-63, OS732, U-2OS, HOS and SAOS-2 cell proliferation. β-Escin also exhibited excellent anti-proliferative and pro-apoptotic effects in an established OS xenograft model. β-Escin and cytotoxic drugs, including cisplatin, methotrexate (MTX), doxorubicin (Dox) and ifosfamide (Ifos), synergistically inhibited proliferation of MG-63 and OS732 cells in vitro. Moreover, β-escin induced apoptotic death, activated caspase-3, caspase-8 and caspase-9, and regulated expression of Bax and Bcl-2 in MG-63 cells. In addition, our results showed that β-escin treatment reduced expression of p-PI3K, p-Akt and p-mTOR both in MG-63 cells and in an MG-63 xenograft OS model. Interestingly, SC79, which is an Akt activator, inhibited the anti-proliferative effects of β-escin on MG-63 cells. Taken together, our data support the conclusion that β-escin effectively inhibits OS proliferation both in vivo and in vitro. The inhibitory effect of β-escin, at least in part, is due to the inactivation of the PI3K/Akt signalling pathway.

β-Escin exhibits anticancer effects on a panel of established cancer cells. However, the effects of β-escin on human osteosarcoma (OS) are still unknown.

Overexpression of CIP2A is associated with poor prognosis in multiple myeloma

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.

Protein phosphatase 2A regulation of markers of extracellular matrix remodelling in hepatocellular carcinoma cells: functional consequences for tumour invasion

BACKGROUND AND PURPOSE

A hallmark of tumour invasion is breakdown of the extracellular matrix due to dysregulation of the matrix metalloproteinase (MMP) system. While our understanding of how this is regulated by kinase signalling pathways is well established, its counter-regulation by protein phosphatases (PP) is poorly understood. Therefore, we investigated the effect of PP inhibition on markers of extracellular remodelling and how PP2A activity modulated MMP-9 abundance and function of Hep3B cells.

EXPERIMENTAL APPROACH

Cells were exposed to okadaic acid (OA), tautomycetin and cyclosporin A, and the expression profile determined using PCR. Effects of OA and a protein inhibitor of PP2A, CIP2A, on MMP-9 abundance, PP2A activity and cell migration were investigated using ELISA, promoter constructs, siRNA knockdown and transwell migration assays.

KEY RESULTS

OA increased expression and abundance of MMP-9 and the tissue inhibitor of MMP, TIMP-1, without affecting other MMPs, TIMPs and ADAMs. The effect on MMP-9 was mimicked by CIP2A overexpression and knockdown of the PPP2CA catalytic, but not PPP2R1A scaffolding, subunit. Cyclosporin A and PPP1CA silencing did not alter MMP-9 expression, while tautomycetin transiently increased it. Mutation of AP-1, but not NF-κB, binding sites inhibited OA-mediated MMP-9 transcriptional activity. OA and CIP2A decreased PP2A activity and increased cell migration.

CONCLUSION AND IMPLICATIONS

OA increased MMP-9 by decreasing PP2A activity and PP2Ac, through AP-1 binding sites on the MMP-9 promoter. The functional consequence of this and CIP2A overexpression was increased cell migration. Hence, PP2A inhibition induced a metastatic phenotype through alterations in MMP-9 in Hep3B cells.

Expression of cancerous inhibitor of protein phosphatase 2A in human triple negative breast cancer correlates with tumor survival, invasion and autophagy

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized oncoprotein which is involved in the progression of several human malignancies. The present study aimed to investigate its biological function in human triple negative breast cancer (TNBC). The expression of CIP2A in TNBC cells was examined and it was observed that CIP2A was elevated in the TNBC cell line compared with poorly invasive breast cancer cells. CIP2A depletion in TNBC cell lines inhibited proliferation, and induced apoptosis and autophagy. In addition, CIP2A depletion inhibited invasion and migration of TNBC cells. Furthermore, CIP2A depletion downregulated Akt/mTOR/P70S6K phosphorylation. These results validate the role of CIP2A as a invasion-associated oncoprotein and established CIP2A as a promising therapeutic target of TNBC.

CIP2A is a poor prognostic factor and can be a diagnostic marker in papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common type of thyroid carcinoma. CIP2A has recently been described as a prognostic marker in many cancers. In this study, we assessed the value of this novel prognostic marker in PTC. A total of 178 surgical specimens of both benign and malignant thyroid tumors were collected. Immunohistochemical staining for CIP2A, HBME-1, galectin-3, and CK19 was performed. Western blotting for CIP2A was also performed. CIP2A was expressed in 85.3% of malignant tumors and 12.1% of benign tumors. ROC analysis showed that the AUC for CIP2A was higher than those for other tumor markers. Western blotting showed that CIP2A expression was higher in PTC than in other tumors. Poor progression-free survival was observed in the high-CIP2A expression group. High CIP2A expression is a poor prognostic factor and can be a diagnostic marker in PTC. The presence of any two of the three indicated makers (CIP2A, galectin-3, and HBME-1) is strongly correlated with the diagnosis of PTC.

All roads lead to PP2A: exploiting the therapeutic potential of this phosphatase

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase involved in the regulation of many cellular processes. A confirmed tumor suppressor protein, PP2A is genetically altered or functionally inactivated in many cancers highlighting a need for its therapeutic reactivation. In this review we discuss recent literature on PP2A: the elucidation of its structure and the functions of its subunits, and the identification of molecular lesions and post-translational modifications leading to its dysregulation in cancer. A final section will discuss the proteins and small molecules that modulate PP2A and how these might be used to target dysregulated forms of PP2A to treat cancers and other diseases.

Shikonin inhibits invasiveness of osteosarcoma through MMP13 suppression

Osteosarcoma (OS) is the most common primary malignant bone tumor, notorious for its metastasis. We have recently shown that shikonin, an effective constituent extracted from Chinese medicinal herb, induces necroptosis in OS cells. Nevertheless, the effects of low-dose shikonin on the invasiveness of OS cells are unknown. Here, we showed that shikonin dose-dependently decreased OS cell invasiveness in both scratch wound healing assay and transwell cell migration assay. Moreover, the direct target of shikonin on cell invasiveness was found to be matrix metalloproteinase (MMP)-13. Further, the inhibitory effects of shikonin on cell invasiveness were completely abolished in MMP13-overexpressing OS cells. Together, these data suggest that shikonin may suppress OS invasiveness through MMP13 suppression. Thus, our data highlight a previous unappreciated role for shikonin in suppressing OS cell metastasis.

PI3K/Akt signaling in osteosarcoma

Osteosarcoma (OS) is the most common nonhematologic bone malignancy in children and adolescents. Despite the advances of adjuvant chemotherapy and significant improvement of survival, the prognosis remains generally poor. As such, the search for more effective anti-OS agents is urgent. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is thought to be one of the most important oncogenic pathways in human cancer. An increasing body of evidence has shown that this pathway is frequently hyperactivated in OS and contributes to disease initiation and development, including tumorigenesis, proliferation, invasion, cell cycle progression, inhibition of apoptosis, angiogenesis, metastasis and chemoresistance. Inhibition of this pathway through small molecule compounds represents an attractive potential therapeutic approach for OS. The aim of this review is to summarize the roles of the PI3K/Akt pathway in the development and progression of OS, and to highlight the therapeutic potential of targeting this signaling pathway. Knowledge obtained from the application of these compounds will help in further understanding the pathogenesis of OS and designing subsequent treatment strategies.

Regulation of PP2A by Sphingolipid Metabolism and Signaling

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that is a primary regulator of cellular proliferation through targeting of proliferative kinases, cell cycle regulators, and apoptosis inhibitors. It is through the regulation of these regulatory elements that gives PP2A tumor suppressor functions. In addition to mutations on the regulatory subunits, the phosphatase/tumor suppressing activity of PP2A is also inhibited in several cancer types due to overexpression or modification of the endogenous PP2A inhibitors such as SET/I2PP2A. This review focuses on the current literature regarding the interactions between the lipid signaling molecules, selectively sphingolipids, and the PP2A inhibitor SET for the regulation of PP2A, and the therapeutic potential of sphingolipids as PP2A activators for tumor suppression via targeting SET oncoprotein.

Oncogenic nexus of cancerous inhibitor of protein phosphatase 2A (CIP2A): an oncoprotein with many hands

Oncoprotein CIP2A a Cancerous Inhibitor of PP2A forms an "oncogenic nexus" by virtue of its control on PP2A and MYC stabilization in cancer cells. The expression and prognostic function of CIP2A in different solid tumors including colorectal carcinoma, head and neck cancers, gastric cancers, lung carcinoma, cholangiocarcinoma, esophageal cancers, pancreatic carcinoma, brain cancers, breast carcinoma, bladder cancers, ovarian carcinoma, renal cell carcinomas, tongue cancers, cervical carcinoma, prostate cancers, and oral carcinoma as well as a number of hematological malignancies are just beginning to emerge. Herein, we reviewed the recent progress in our understanding of (1) how an "oncogenic nexus" of CIP2A participates in the tumorigenic transformation of cells and (2) how we can prospect/view the clinical relevance of CIP2A in the context of cancer therapy. The review will try to understand the role of CIP2A (a) as a biomarker in cancers and evaluate the prognostic value of CIP2A in different cancers (b) as a therapeutic target in cancers and (c) in drug response and developing chemo-resistance in cancers.

Establishment and analysis of osteosarcoma cell sublines with different metastatic characteristics

The aim of this study is to establish human osteosarcoma MG-63 cell sublines with different metastatic characteristics and provide good experimental models for mechanism study of osteosarcoma metastasis. Six cell sublines were screened and established by using the in vitro cloning technology. In vitro invasion experiments, cellular electrophoretic mobility determinations, cellular proliferation rate determinations, and soft agar clone formation assays were used to compare, analyze, and identify the metastatic characteristics of various cell sublines. The results indicated that the invasion capacity, cellular electrophoretic mobility, cell proliferation, and soft agar clone formation capacity of A2, A3, and A16 sublines were higher than those of A1, A6, and A20 sublines. There was no significant difference in various values determined among A2, A3, and A16, and among A1, A6, and A20 (P > 0.05), but there were significant differences in various values determined between the former three and the latter three (P < 0.05). In conclusion, MG-63 cell sublines with different metastatic characteristics can be established by combining several technologies and can contribute to further research on the mechanism of osteosarcoma metastasis.