Cancerous Inhibitor Of Protein Phosphatase 2A Research Articles

Abstract P3-07-12: Targeting SET to disrupt oncogenic CIP2A feedforward loop shows therapeutic potential in triple negative breast cancer cells

Abstract Triple-negative breast cancer (TNBC) remains a difficult-to-treat cancer with a need for new therapeutic target. The serine/threonine protein phosphatase 2A (PP2A) functions as a tumor suppressor and enhancing PP2A activity by PP2A-activating agents is a promising anti-cancer approach. There are intrinsic inhibitors of PP2A including SET and cancerous inhibitor of protein phosphatase 2A (CIP2A), both of which interact and inhibit PP2A, playing oncogenic roles. Here we studied the tumor promoting effects of SET and CIP2A and discovered a potent linkage between SET and CIP2A-feedforward pathway in TNBC. We further demonstrated the anticancer activity of a novel SET/PP2A protein-protein interaction inhibitor, TD-19. Analyzing TCGA and clinical TNBC cohort, SET and CIP2A overexpressions correlated with worse survival in TNBC patients. Tumors from TNBC patients with higher SET expressions were significantly associated with higher Ki-67 and p-Akt expressions. Table 1 High SET H score (>180) N=21Low SET H score (<=180) N=70P valueAge [median (range)]54 (36-69)56 (30-88)0.185Primary tumor (T) 0.99916 (28.6)21 (30.0) 213 (61.9)43 (61.4) 3-42 (9.5)6 (8.6) Nodal status (N) 0.12208 (38.1)45 (64.3) 17 (33.3)12 (17.1) 2-36 (28.6)13 (18.6) Stage 0.49812 (9.5)14 (20.0) 213 (61.9)41 (58.6) 36 (28.6)15 (21.4) Grade 0.78311 (4.8)4 (5.7) 28 (38.1)21 (30.0) 312 (57.1)45 (64.3) Tumor necrosis13 (61.9)40 (57.1)0.698Lymphovascular invasion6 (30.0)15 (21.4)0.549CIP2A [median (range)]120 (40-220)100 (30-300)0.253p-Akt [median (range)]200 (65-300)160 (20-300)0.011Ki-67 [median (range)]30 (0-87.5)22.5 (0-85)0.004 Consistent with clinical results, TNBC cells with ectopic overexpression of SET and CIP2A showed significantly increased cell proliferation, migration and invasion, and colony-formation. Moreover, TD-19 demonstrated anti-tumor effects through inhibiting SET-PP2A interaction and CIP2A/PP2A/pAkt-mediated pathway in vitro and in a TNBC xenograft mouse model. Mechanistically, TD19 downregulated CIP2A mRNA via affecting Elk-1 amount in nucleus thereby decreased the binding of Elk-1 to the CIP2A-promotor. Furthermore, given that ERK-dependent phosphorylation of Elk-1 is essential for Elk-1 shuttling from cytoplasm to nucleus and PP2A controls ERK activation (phosphorylation), we hypothesized a CIP2A-feedforward loop consisting of pERK/pElk-1/CIP2A/PP2A may contribute to the oncogenesis in TNBC. Indeed, with TD19 treatment, SET/PP2A interaction was inhibited, PP2A activity was increased, and expressions of the CIP2A-feedforward loop members were suppressed. This loop was validated by knockdown of PP2A and ectopic expression of Elk-1. In addition, ectopic expression of SET increased pAkt, pERK, pElk-1 and CIP2A expressions, suggesting a positive linkage between SET and CIP2A feedforward signaling. Importantly, combining TD-19 with cisplatin demonstrated enhanced anti-proliferative and apoptotic effects in association with CIP2A downregulation in vitro. In summary, we discover a novel oncogenic CIP2A-feedforward loop in TNBC and targeting SET to disrupt oncogenic CIP2A feedforward loop shows therapeutic potential in TNBC. Citation Format: Huang T-T, Liu C-Y, Chen Y-T, Chu P-Y, Huang C-T, Wang W-L, Wu C-Y, Shiau C-W, Chen K-F, Tseng L-M. Targeting SET to disrupt oncogenic CIP2A feedforward loop shows therapeutic potential in triple negative breast cancer cells [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-07-12.

Oncoprotein CIP2A is stabilized via interaction with tumor suppressor PP2A/B56.

Protein phosphatase 2A (PP2A) is a critical human tumor suppressor. Cancerous inhibitor of PP2A (CIP2A) supports the activity of several critical cancer drivers (Akt, MYC, E2F1) and promotes malignancy in most cancer types via PP2A inhibition. However, the 3D structure of CIP2A has not been solved, and it remains enigmatic how it interacts with PP2A. Here, we show by yeast two-hybrid assays, and subsequent validation experiments, that CIP2A forms homodimers. The homodimerization of CIP2A is confirmed by solving the crystal structure of an N-terminal CIP2A fragment (amino acids 1-560) at 3.0 Å resolution, and by subsequent structure-based mutational analyses of the dimerization interface. We further describe that the CIP2A dimer interacts with the PP2A subunits B56α and B56γ. CIP2A binds to the B56 proteins via a conserved N-terminal region, and dimerization promotes B56 binding. Intriguingly, inhibition of either CIP2A dimerization or B56α/γ expression destabilizes CIP2A, indicating opportunities for controlled degradation. These results provide the first structure-function analysis of the interaction of CIP2A with PP2A/B56 and have direct implications for its targeting in cancer therapy.

CIP2A, an oncoprotein, is associated with cell proliferation, invasion and migration in laryngeal carcinoma cells.

Laryngeal carcinoma is one of the most common malignant tumors in otorhinolaryngology. Moreover, experimental investigation showed that cancerous inhibitor of protein phosphatase 2A (CIP2A) expressed highly in various cancers. Therefore, we investigated whether CIP2A can regulate the proliferation, invasion and migration by RNA interference in Hep-2 cells and AMC-NH-8 cells and further affect the activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. Overexpression of CIP2A was evaluated in tumor tissue and laryngeal cancer cell lines (Hep-2 and AMC-NH-8 cells) by real-time quantitative polymerase chain reaction (RT-qPCR) and western blot assay. In a follow-up experiment, we confirmed that CIP2A siRNA effectively suppressed the cell proliferation at 48 and 72h, and arrested cell cycle at G0/G1 in Hep-2 cells and AMC-NH-8 cells. The invasion and migration of cell in siRNA CIP2A group were markedly inhibited. Moreover, the experimental results showed that the expression levels of invasion- and migration-related genes, including E-cadherin, metastasis-associated gene 1 (MTA1) and matrix metalloproteinases-2/9 (MMP-2/9), were regulated by CIP2A siRNA. Phosphorylation levels of PI3K and AKT proteins were reduced by CIP2A siRNA. Importantly, it suggested signaling through PI3K/Akt as a critical mechanism by which CIP2A siRNA may suppress cell proliferation, invasion and migration in laryngeal carcinoma cells.

CIP2A acts as a scaffold for CEP192-mediated microtubule organizing center assembly by recruiting Plk1 and aurora A during meiotic maturation.

In somatic cells spindle microtubules are nucleated from centrosomes that act as major microtubule organizing centers (MTOCs), whereas oocytes form meiotic spindles by assembling multiple acentriolar MTOCs without canonical centrosomes. Aurora A and Plk1 are required for these events, but the underlying mechanisms remain largely unknown. Here we show that CIP2A regulates MTOC organization by recruiting aurora A and Plk1 at spindle poles during meiotic maturation. CIP2A colocalized with pericentrin at spindle poles with a few distinct cytoplasmic foci. Although CIP2A has been identified as an endogenous inhibitor of protein phosphatase 2A (PP2A), overexpression of CIP2A had no effect on meiotic maturation. Depletion of CIP2A perturbed normal spindle organization and chromosome alignment by impairing MTOC organization. Importantly, CIP2A was reciprocally associated with CEP192, promoting recruitment of aurora A and Plk1 at MTOCs. CIP2A was phosphorylated by Plk1 at S904, which targets CIP2A to MTOCs and facilitates MTOC organization with CEP192. Our results suggest that CIP2A acts as a scaffold for CEP192-mediated MTOC assembly by recruiting Plk1 and aurora A during meiotic maturation in mouse oocytes.

Arctigenin inhibits triple-negative breast cancers by targeting CIP2A to reactivate protein phosphatase 2A.

We have shown that a novel STAT3 inhibitor arctigenin(Atn) induces significant cytotoxicity in triple-negative breast cancer(TNBC) cells. This study further delineated molecular mechanisms where by Atn triggered cytotoxicity in TNBC cells. We found Atn can also inhibit metastasis in TNBC cells through cancerous inhibitor of protein phosphatase2A(CIP2A) pathway. CIP2A is an endogenous inhibitor of protein phosphatase2A(PP2A), which can increase the migration and invasion of various cancer cells. PP2A is a tumor suppressor, which is functionally defective in various cancers. Atn-induced metastasis inhibition was associated with reactivation of PP2A, downregulation of CIP2A and Akt phosphorylation. Silencing CIP2A enhanced Atn-induced metastasis inhibition and apoptosis in TNBCs. Furthermore, ectopic expression of CIP2A or inhibition of PP2A in TNBC cells abolished the effects of Atn. In conclusion, we found that enhancement of PP2A activity by inhibition of CIP2A, at least in part, promotes the anti-metastasis effect induced by Atn. Our findings disclose the novel therapeutic mechanism of this targeted agent, and suggest the therapeutic potential and feasibility of developing PP2A enhancers as a novel anticancer strategy.

CucurbitacinB induces autophagy and apoptosis by suppressing CIP2A/PP2A/mTORC1 signaling axis in human cisplatin resistant gastric cancer cells.

Cancerous inhibitor of protein phosphatase2A (CIP2A) is a human oncoprotein that is overexpressed in multiple kinds of tumors including gastric cancer(GC). Mammalian target of rapamycin complex1 (mTORC1) over-activation is detected in GC and many other cancers. Previous study found that CIP2A/mTORC1 controls cell growth and autophagy through direct association. CIP2A plays an 'oncogenic nexus' in several cancer types to participate in the tumorigenic transformation and chemoresistance. In the present study, we investigated whether CucurbitacinB(CuB), a natural compound found in Cucurbitaceae, can be used in cisplatin (DDP)-resistant human GC cell line SGC7901/DDP. Results demonstrated that CuB treatment significantly suppressed SGC7901/DDP cell proliferation, induced caspase-dependent apoptosis, and autophagy. The activation of autophagy was mediated through CuB-induced inhibition of mTORC1. Furthermore, CuB inhibited mTORC1 via the activation of protein phosphatase2A(PP2A) which is mediated by CIP2A inhibition. These findings indicated that CuB can inhibit the proliferation, induce caspase-dependent apoptosis, and autophagy of SGC7901/DDP cells by suppressing CIP2A/PP2A/mTORC1 signaling axis. Thus, CuB may be a novel effective candidate to treat DDP-resistant human GC 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.

Gambogenic acid induces proteasomal degradation of CIP2A and sensitizes hepatocellular carcinoma to anticancer agents

Cancerous inhibitor of protein phosphatase2A (CIP2A) is an oncoprotein that is overexpressed in many human malignancies. It regulates phosphorylated AKT and stabilizes c‑Myc in cell proliferation and tumor formation, suggesting that CIP2A plays an essential role in the development of cancer. In the present study, we report that a natural compound, gambogenic acid(GEA), induced the degradation of CIP2A via the ubiquitin‑proteasome pathway. Interestingly, the combination of GEA and proteasome inhibitors potentiated the accumulation of ubiquitinated CIP2A and aggresome formation. In addition, GEA exhibited an inhibitory effect on cell proliferation and CIP2A‑downstream signaling molecules (c‑Myc and pAKT). Furthermore, GEA and CIP2A silencing enhanced the chemosensitivity of hepatocellular carcinoma cells to anticancer agents, suggesting that a combination of a CIP2A inhibitor and anticancer agents could be a valuable clinical therapeutic strategy. These results indicate that GEA is a CIP2A inhibitor that interferes with the ubiquitination and destabilization of CIP2A, providing a promising strategy to enhance the combinational therapy for hepatocellular carcinoma.

CIP2A regulates proliferation and apoptosis of multiple myeloma cells.

Multiple myeloma (MM) is one of the most common causes of mortality from hematological malignancy in China. Recent studies have demonstrated that cancerous inhibitor of protein phosphatase2A (CIP2A) may exhibit a role in promoting the growth of cancer; however, the function of CIP2A in MM remains unknown. In the present study, the expression and molecular mechanism underlying the effects of CIP2A in patients with MM and in MM cell lines were elucidated. Firstly, the expression of CIP2A was detected in patients with MM and in MM cell lines by reverse transcription‑quantitative polymerase chain reaction. Furthermore, silencing of CIP2A with short hairpin RNA was performed in MM cells, and the impact on the proliferation and apoptosis of RPMI‑8226 cells was analyzed (as endogenous CIP2A is highly expressed in RPMI‑8226 cell lines compared with other cells). CIP2A was significantly elevated in patients with MM and in MM cell lines, and silencing of CIP2A could inhibit the proliferation ability of RPMI‑8226 cells invitro. In addition, CIP2A knockdown induced apoptosis and led to substantial reduction of c‑Myc protein levels in MM cell lines. This study suggested that CIP2A inhibition may provide a promising therapeutic strategy for patients with MM.

Abstract 3065: Erlotinib derivative, devoid of EGFR kinase inhibiting effect, induced apoptosis of triple-negative breast cancer cells through modulating Elk-1/CIP2A signaling pathway

Abstract Background: Triple-negative breast cancer (TNBC), a subgroup of breast cancer, is characterized by its aggressive nature and poor prognosis. Therefore, the discovery and identification of new therapeutic molecule is currently one of urgent issues. Previous studies have suggested an oncoprotein, cancerous inhibitor of protein phosphatase 2A (CIP2A), is a potential therapeutic determinant that mediates the anti-cancer effects of several new agents. We have developed an erlotinib analogue TD-19 that is devoid of EGFR tyrosine kinase inhibition effect, and demonstrated its anti-tumor effects through the suppression of CIP2A-mediated pathway in non-small-cell lung cancer cells (J Pharmacol Exp Ther 2014). In this study, we tested the apoptotic effect of TD-19 in TNBC cells and examined the drug mechanism upstream of CIP2A. Methods: TNBC cell lines were used for in vitro studies. Cell viability was examined by MTT assay. Apoptosis was examined by flow cytometry and western blot. Signal transduction pathways in cells were assessed by western blot. In vivo efficacy of TD-19 was tested in nude mice with breast cancer xenografts. Results: TD-19 triggered significant apoptosis in MDA-MB-231, MDA-MB-468, MDA-MB-468 and BT-20 cell lines, as well as in non-TNBC cell lines (SK-BR3 and MCF-7). The induced apoptotic effects are associated with CIP2A and p-Akt downregulation in both dose- and time-dependent manners. Overexpression of CIP2A protected MDA-MB-468 from the induced apoptosis of TD-19. In addition, PP2A activity was increased in TD-19 treated MDA-MB-468 cells. Moreover, forskolin, a protein phosphatase 2A (PP2A) activator, enhanced the cell death induced by TD-19, whereas okadaic acid, a PP2A antagonist, attenuated the apoptosis. Mechanistically, we demonstrated that TD-19 downregulated CIP2A mRNA expression through affecting the total amount of Elk-1 in nucleus. Chromatin immunoprecipitation experiments showed TD-19 disturbed the binding of Elk-1 to the proximal CIP2A-promotor. Furthermore, TD-19 showed anti-tumor activity in mice bearing MDA-MB-468 xenograft tumors, and downregulated CIP2A as well as p-Akt in these xenografted tumors. Interestingly, combining TD-19 with cisplatin demonstrated enhanced anti-proliferative and apoptotic effects in association with CIP2A downregulation in vitro. Conclusions: Our results suggest that the novel erlotinib derivative (TD-19) induced apoptosis through inhibiting Elk1/CIP2A/PP2A/p-Akt signaling in TNBC cells. Pharmacological modulation of Elk-1/CIP2A signaling may be a therapeutic strategy for TNBC. (Supported by Yen Tjing Ling Medical Foundation (CI-104-07); MOST 104-2628-B-075-001-MY3; Yang-Ming Branch of Taipei City Hospital; and from the Ministry of Health and Welfare, Executive Yuan, Taiwan, MOHW104-TDU-B-211-124-001; and MOHW103TDU-212-114002). Citation Format: Ling-Ming Tseng, Yi-Ting Chen, Chun-Teng Huang, Pei-Yi Chu, Wan-Lun Wang, Chun-Yu Liu, Chung-Wai Shiau, Kuen-Feng Chen. Erlotinib derivative, devoid of EGFR kinase inhibiting effect, induced apoptosis of triple-negative breast cancer cells through modulating Elk-1/CIP2A signaling pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3065.

Genistein targets the cancerous inhibitor of PP2A to induce growth inhibition and apoptosis in breast cancer cells.

Genistein is a soy isoflavone with phytoestrogen and tyrosine kinase inhibitory properties. High intake of soy/genistein has been associated with reduced breast cancer risk. Despite the advances in genistein-mediated antitumor studies, the underlying mechanisms remain unclear. In the present study, we investigated genistein-induced regulation of the cancerous inhibitor of protein phosphatase 2A (CIP2A), a novel oncogene frequently overexpressed in breast cancer, and its functional impact on genistein-induced growth inhibition and apoptosis. We demonstrated that genistein induced downregulation of CIP2A in MCF-7-C3 and T47D breast cancer cells, which was correlated with its growth inhibition and apoptotic activities. Overexpression of CIP2A attenuated, whereas CIP2A knockdown sensitized, genistein-induced growth inhibition and apoptosis. We further showed that genistein-induced downregulation of CIP2A involved both transcriptional suppression and proteasomal degradation. In particular, genistein at higher concentrations induced concurrent downregulation of E2F1 and CIP2A. Overexpression of E2F1 attenuated genistein-induced downregulation of CIP2A mRNA, indicating the role of E2F1 in genistein-induced transcriptional suppression of CIP2A. Taken together, our results identified CIP2A as a functional target of genistein and demonstrated that modulation of E2F1-mediated transcriptional regulation of CIP2A contributes to its downregulation. These data advance our understanding of genistein-induced growth inhibition and apoptosis, and support further investigation on CIP2A as a therapeutic target of relevant anticancer agents.

The expression of cancerous inhibitor protein phosphatase 2A in chronic rhinosinusitis with nasal polyps

Conclusion: The study suggests that cancerous inhibitor of protein phosphatase 2A (CIP2A) expression and eosinophilia associate with chronic rhinosinusitis with nasal polyps with aspirin exacerbated respiratory disease (CRSwNP + AERD). Further studies with a larger sample size are needed to evaluate further the role of CIP2A and related pathways in CRSwNP + AERD.Objectives: Low prostaglandin E2 levels putatively associate with CRSwNP + AERD and decreased c-Myc levels. The aim of this study was to evaluate the expression and revision-predictive role of oncoprotein CIP2A, another c-Myc modulator, in CRSwNP with/without AERD, and in antrochoanal polyps.Method: Ninety retrospective archival objective glasses of nasal polyp tissue from CRSwNP or ACP patients were used for assessing mucosal eosinophilia. Of this population, 90 archival nasal polyp specimens were available for immunohistochemical staining with a polyclonal anti-CIP2A antibody, together with 19 control nasal mucosa specimens. CIP2A staining intensity and tissue eosinophilia were assessed by two blinded observers with a light microscope. Subject characteristics from 90 patients and 19 controls were obtained from patient records and additionally by a questionnaire from controls. The follow-up data was available from patient records of 84 patients and 16 controls.Results: The expression of epithelial CIP2A was detected both in control inferior turbinate mucosa and nasal polyps. The expression was significantly lower in the CRSwNP + AERD group compared to controls and CRSwNP without AERD (p < 0.01). High mucosal eosinophilia associated with CRSwNP (p < 0.01). Neither CIP2A nor eosinophilia predicted the need for revision surgery (p > 0.05), whereas previous surgery, allergic rhinitis, and use of corticosteroids did predict the need for revision surgery (p < 0.05).

Cucurbitacin B reverses multidrug resistance by targeting CIP2A to reactivate protein phosphatase 2A in MCF-7/adriamycin cells.

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a human oncoprotein that is overexpressed in various tumors. A previous study found that CIP2A expression is associated with doxorubicin (Dox) resistance. In the present study, we investigated whether cucurbitacin B (CuB), a natural anticancer compound found in Cucurbitaceae, reversed multidrug resistance (MDR) and downregulated CIP2A expression in MCF-7/Adriamycin (MCF-7/Adr) cells, a human breast multidrug-resistant cancer cell line. CuB treatment significantly suppressed MCF-7/Adr cell proliferation, and reversed Dox resistance. CuB treatment also induced caspase-dependent apoptosis, decreased phosphorylation of Akt (pAkt). The suppression of pAkt was mediated through CuB-induced activation of protein phosphatase 2A (PP2A). Furthermore, CuB activated PP2A through the suppression of CIP2A. Silencing CIP2A enhanced CuB-induced growth inhibition, apoptosis and MDR inhibition in MCF-7/Adr cells. In conclusion, we found that enhancement of PP2A activity by inhibition of CIP2A promotes the reversal of MDR induced by CuB.

The prognostic significance of cancerous inhibitor of PP2A (CIP2A) expression in cervical cancer (CC).

e17019Background: CIP2A is a newly elucidated oncogene that demonstrates high expression in many human cancers. CIP2A may not only serve as a drug target, but may play a role as a biomarker, predic...

CIP2A Promotes T-Cell Activation and Immune Response to Listeria monocytogenes Infection.

The oncoprotein Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) is overexpressed in most malignancies and is an obvious candidate target protein for future cancer therapies. However, the physiological importance of CIP2A-mediated PP2A inhibition is largely unknown. As PP2A regulates immune responses, we investigated the role of CIP2A in normal immune system development and during immune response in vivo. We show that CIP2A-deficient mice (CIP2AHOZ) present a normal immune system development and function in unchallenged conditions. However when challenged with Listeria monocytogenes, CIP2AHOZ mice display an impaired adaptive immune response that is combined with decreased frequency of both CD4+ T-cells and CD8+ effector T-cells. Importantly, the cell autonomous effect of CIP2A deficiency for T-cell activation was confirmed. Induction of CIP2A expression during T-cell activation was dependent on Zap70 activity. Thus, we reveal CIP2A as a hitherto unrecognized mediator of T-cell activation during adaptive immune response. These results also reveal CIP2AHOZ as a possible novel mouse model for studying the role of PP2A activity in immune regulation. On the other hand, the results also indicate that CIP2A targeting cancer therapies would not cause serious immunological side-effects.

Oridonin inhibits gefitinib-resistant lung cancer cells by suppressing EGFR/ERK/MMP-12 and CIP2A/Akt signaling pathways.

Oridonin (Ori), a diterpenoid compound extracted from traditional medicinal herbs, elicits antitumor effects on many cancer types. However, whether Ori can be used in gefitinib-resistant non-small cell lung cancer (NSCLC) cells remains unclear. This study investigated the antitumor activity and underlying mechanisms of Ori. Results demonstrated that this compound dose-dependently inhibited the proliferation, invasion, and migration of the gefitinib-resistant NSCLC cells invitro. Ori also significantly downregulated the phosphorylation of EGFR, ERK, Akt, expression levels of matrix metalloproteinase-12 (MMP-12), and the cancerous inhibitor of protein phosphatase 2A (CIP2A). In addition, Ori upregulated protein phosphatase 2A (PP2A) activity of gefitinib-resistant NSCLC cells. Ori combined with docetaxel synergistically inhibited these cells. Ori also inhibited tumor growth in murine models. Immunohistochemistry results further revealed that Ori downregulated phospho-EGFR, MMP-12, and CIP2A invivo. These findings indicated that Ori can inhibit the proliferation, invasion, and migration of gefitinib-resistant NSCLC cells by suppressing EGFR/ERK/MMP-12 and CIP2A/PP2A/Akt signaling pathways. Thus, Ori may be a novel effective candidate to treat gefitinib-resistant NSCLC.

HDAC1 controls CIP2A transcription in human colorectal cancer cells.

This work describes the effectiveness of HDAC-inhibitor (S)-2 towards colorectal cancer (CRC) HCT116 cells in vitro by inducing cell cycle arrest and apoptosis, and in vivo by contrasting tumour growth in mice xenografts. Among the multifaceted drug-induced events described herein, an interesting link has emerged between the oncoprotein histone deacetylase HDAC1 and the oncogenic Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) which is overexpressed in several cancers including CRCs. HDAC1 inhibition by (S)-2 or specific siRNAs downregulates CIP2A transcription in three different CRC cell lines, thus restoring the oncosuppressor phosphatase PP2A activity that is reduced in most cancers. Once re-activated, PP2A dephosphorylates pGSK-3β(ser9) which phosphorylates β-catenin that remains within the cytosol where it undergoes degradation. The decreased amount/activity of β-catenin transcription factor prompts cell growth arrest by diminishing c-Myc and cyclin D1 expression and abrogating the prosurvival Wnt/β-catenin signaling pathway. These results are the first evidence that the inhibition of HDAC1 by (S)-2 downregulates CIP2A transcription and unleashes PP2A activity, thus inducing growth arrest and apoptosis in CRC cells.

FTY720-induced enhancement of autophagy protects cells from FTY720 cytotoxicity in colorectal cancer.

FTY720, also known as fingolimod, is a widely used immunomodulator in multiple sclerosis and multiple organ transplantation. It is also an important protein phosphatase 2A (PP2A) activator. Based on this, a number of studies have recently demonstrated the cytotoxic effect of FTY720 in various cancers. Yet in colorectal cancer (CRC), the underlying mechanisms of FTY720 cytotoxicity remain less clear, especially the relationship between a drug and autophagy. We demonstrate here for the first time that FTY720 promotes the appearance of autophagic hallmarks such as autophagosome formation and light chain 3 (LC3)-II accumulation, indicating the participation of autophagy in FTY720 cytotoxicity on CRC. Moreover, inhibition of autophagy using 3-methyladenine (3-MA), a specific inhibitor of autophagy, enhanced FTY720 cytotoxicity, indicating the protective role of autophagy against the drug's own cytotoxic effect. The protective autophagy was likely affected by cancerous inhibitor of PP2A (CIP2A), an endogenous PP2A inhibitor that is closely related with poor prognosis and drug resistance. Consequently, our data not only demonstrate a new mechanism underlying the cytotoxic effect of FTY720 in CRC, but also a new strategy for CRC treatment, especially in cases resistant to conventional chemotherapies because of high CIP2A levels.

MYC is not detected in highly proliferating normal spermatogonia but is coupled with CIP2A in testicular cancers.

High MYC expression is linked to proliferative activity in most normal tissues and in cancer. MYC also supports self-renewal and proliferation of many types of tissue progenitor cells. Cancerous inhibitor of PP2A (CIP2A) promotes MYC phosphorylation and activity during intestinal crypt regeneration in vivo and in various cancers. CIP2A also supports male germ cell proliferation in vivo. However, the role of MYC in normal germ cell proliferation and spermatogonial progenitor self-renewal is currently unclear. Here, we demonstrate that male germ cells are CIP2A-positive but lack detectable levels of MYC protein; whereas MYC is highly expressed in Leydig cells and peritubular myoid cells contributing thereby to the testicular stem cell niche. On the other hand, MYC was co-expressed with CIP2A in testicular cancers. These results demonstrate that CIP2A and MYC are spatially uncoupled in the regulation of spermatogenesis, but functional relationship between these two human oncoproteins is established during testicular cancer transformation. We propose that further analysis of mechanisms of MYC silencing in spermatogonial progenitors may reveal novel fundamental information relevant to understanding of MYC expression in cancer.

High CIP2A levels correlate with an antiapoptotic phenotype that can be overcome by targeting BCL-XL in chronic myeloid leukemia.

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a predictive biomarker of disease progression in many malignancies, including imatinib-treated chronic myeloid leukemia (CML). Although high CIP2A levels correlate with disease progression in CML, the underlying molecular mechanisms remain elusive. In a screen of diagnostic chronic phase samples from patients with high and low CIP2A protein levels, high CIP2A levels correlate with an antiapoptotic phenotype, characterized by downregulation of proapoptotic BCL-2 family members, including BIM, PUMA and HRK, and upregulation of the antiapoptotic protein BCL-XL. These results suggest that the poor prognosis of patients with high CIP2A levels is due to an antiapoptotic phenotype. Disrupting this antiapoptotic phenotype by inhibition of BCL-XL via RNA interference or A-1331852, a novel, potent and BCL-XL-selective inhibitor, resulted in extensive apoptosis either alone or in combination with imatinib, dasatinib or nilotinib, both in cell lines and in primary CD34+ cells from patients with high levels of CIP2A. These results demonstrate that BCL-XL is the major antiapoptotic survival protein and may be a novel therapeutic target in CML.