CIP2A signature reveals the MYC dependency of CIP2A-regulated phenotypes and its clinical association with breast cancer subtypes

Abstract

Protein phosphatase 2A (PP2A) is a critical human tumor-suppressor complex. A recently characterized PP2A inhibitor protein, namely cancerous inhibitor of PP2A (CIP2A), has been found to be overexpressed at a high frequency in most of the human cancer types. However, our understanding of gene expression programs regulated by CIP2A is almost absent. Moreover, clinical relevance of the CIP2A-regulated transcriptome has not been addressed thus far. Here, we report a high-confidence transcriptional signature regulated by CIP2A. Bioinformatic pathway analysis of the CIP2A signature revealed that CIP2A regulates several MYC-dependent and MYCindependent gene programs. With regard to MYCindependent signaling, JNK2 expression and transwell migration were inhibited by CIP2A depletion, whereas MYC depletion did not affect either of these phenotypes. Instead, depletion of either CIP2A or MYC inhibited cancer cell colony growth with statistically indistinguishable efficiency. Moreover, CIP2A depletion was shown to regulate the expression of several established MYC target genes, out of which most were MYC-repressed genes. CIP2A small-interfering RNA-elicited inhibition of colony growth or activation of MYC-repressed genes was reversed at large by concomitant PP2A inhibition. Finally, the CIP2A signature was shown to cluster with basal-type and human epidermal growth factor receptor (HER)2-positive (HER2 þ ) breast cancer signatures. Accordingly, CIP2A protein expression was significantly associated with basal-like (P ¼ 0.0014) and HER2 þ (Po0.0001) breast cancers. CIP2A expression also associated with MYC gene amplification (Po0.001). Taken together, identification of CIP2A-driven transcriptional signature, and especially novel MYC-independent signaling programs regulated by CIP2A, provides important resource for understanding CIP2A's role as a clinically relevant human oncoprotein. With regard to MYC, these results both validate CIP2A's role in regulating MYC-mediated gene expression and provide a plausible novel explanation for the high MYC activity in basal-like and HER2 þ breast cancers.

CIP2A expression predicts recurrences of tamoxifen-treated breast cancer

“…9,11,18 Of note, CIP2A is weakly expressed in normal breast tissue as protein and transcript. 7,15 Similar to the study of Tseng et al (2012) 37 and Choi et al, 38 in this study the H-score was used to obtain more information on the distribution of CIP2A scores and intensities.…”

“…7,9,[12][13][14][15][16][17] Our interest in CIP2A stems from its inhibitory activity on protein phosphatase 2A (PP2A), which results in protection of MYC from dephosphorylation thereby stabilising the oncogenic stimulation of MYC on cell proliferation. 7,18,19 The mechanism of CIP2A-dependent inhibition of PP2A is not well understood, although some suggest that CIP2A binds to the PP2A catalytic subunit allosterically at the interface where it binds the regulatory B subunit, thus altering substrate specificity and/or limiting activity. 8,[19][20][21][22] In a chronic myeloid leukaemia (CML) model, knockdown of CIP2A results in decreased BCR-ABL1 tyrosine kinase activity.…”

“…16 A CIP2A transcriptional signature suggests that CIP2A promotes MYC signalling pathway but also other pathways as the c-jun N-terminal kinase 2 (JNK2). 7,18 CIP2A is involved in the regulation of a major group of genes that mediate cellular migration. High CIP2A has been correlated with the mesenchymal phenotype in prostate cancer defined by low expression of E-cadherin and higher expression of N-cadherin and vimentin.…”

“…This may explain the correlation between CIP2A overexpression and more aggressive tumour phenotypes and lymph node positivity. 18,24 In light of the involvement of CIP2A in cellular migration and therapeutic resistance, we aimed to investigate CIP2A expression within BCER+ patients. In particular, we were interested to assess whether CIP2A had a role in tamoxifen resistance and therefore whether its expression levels could be used to improve prognostication or therapy prediction in breast cancer.…”

Estradiol enhances CIP2A expression by the activation of p70 S6 kinase

“…Cancerous inhibitor of PP2A (CIP2A), which is known to enhance the migration and proliferation of tumor cells, is overexpressed in various types of human cancers, including breast (Come et al 2009, Niemela et al 2012, Tseng et al 2012, Laine et al 2013, prostate (Vaarala et al 2010), lung (Dong et al 2011), pancreatic (Wang et al 2013), bladder (Huang et al 2012a), blood or bone marrow (Lucas et al 2011, colon (Teng et al 2012), ovarian (Bockelman et al 2011b), cervical (Huang et al 2010), tongue (Bockelman et al 2011a), oral (Basile & Czerninski 2010), esophageal squamous (Qu et al 2012), and head and neck squamous (Ferreira et al 2004) cancers. CIP2A expression is transcriptionally enhanced by Ets1 (Zhao et al 2010), and the concurrent binding of Ets1 and Elk1 to the proximal CIP2A promoter is absolutely required for CIP2A expression in cervical, endometrial, and liver carcinoma cell lines (Huang et al 2012b, Pallai et al 2012.…”