ETS1 Mediates MEK1/2-Dependent Overexpression of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) in Human Cancer Cells

EGFR-MEK-ERK signaling pathway has an established role in promoting malignant growth and disease progression in human cancers. Therefore identification of transcriptional targets mediating the oncogenic effects of the EGFR-MEK-ERK pathway would be highly relevant. Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized human oncoprotein. CIP2A promotes malignant cell growth and is over expressed at high frequency (40–80%) in most of the human cancer types. However, the mechanisms inducing its expression in cancer still remain largely unexplored. Here we present systematic analysis of contribution of potential gene regulatory mechanisms for high CIP2A expression in cancer. Our data shows that evolutionary conserved CpG islands at the proximal CIP2A promoter are not methylated both in normal and cancer cells. Furthermore, sequencing of the active CIP2A promoter region from altogether seven normal and malignant cell types did not reveal any sequence alterations that would increase CIP2A expression specifically in cancer cells. However, treatment of cancer cells with various signaling pathway inhibitors revealed that CIP2A mRNA expression was sensitive to inhibition of EGFR activity as well as inhibition or activation of MEK-ERK pathway. Moreover, MEK1/2-specific siRNAs decreased CIP2A protein expression. Series of CIP2A promoter-luciferase constructs were created to identify proximal −27 to −107 promoter region responsible for MEK-dependent stimulation of CIP2A expression. Additional mutagenesis and chromatin immunoprecipitation experiments revealed ETS1 as the transcription factor mediating stimulation of CIP2A expression through EGFR-MEK pathway. Thus, ETS1 is probably mediating high CIP2A expression in human cancers with increased EGFR-MEK1/2-ERK pathway activity. These results also suggest that in addition to its established role in invasion and angiogenesis, ETS1 may support malignant cellular growth via regulation of CIP2A expression and protein phosphatase 2A inhibition

Regulation and Clinical Relevance of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) In Human Cancers

Tässä väitöskirjatyössä tutkittiin niitä mekanismeja, joilla hiljattain löydettyä syöpägeeniä CIP2A säädellään, sekä selvitettiin ensimmäistä kertaa CIP2A:n merkitystä ihmisen syövissä. Tämä väitöskirja on ensimmäinen CIP2A syöpägeenistä tehty väitöskirja maailmassa.Current study is the first PhD thesis in the world on a newly identified cancer causing protein Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A). This study identifies the mechanisms that drive the expression of this newly identified cancer causing protein,CIP2A, in human cancers. We identify new signaling pathways which involve some well established cancer causing genes like MYC. In addition to the mechanisms , we also demonstrate the clinical relevance, in the form of prognostic role, of CIP2A in human cancers for the first time

Regulation and Clinical Relevance of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) In Human Cancers

Tässä väitöskirjatyössä tutkittiin niitä mekanismeja, joilla hiljattain löydettyä syöpägeeniä CIP2A säädellään, sekä selvitettiin ensimmäistä kertaa CIP2A:n merkitystä ihmisen syövissä. Tämä väitöskirja on ensimmäinen CIP2A syöpägeenistä tehty väitöskirja maailmassa.Current study is the first PhD thesis in the world on a newly identified cancer causing protein Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A). This study identifies the mechanisms that drive the expression of this newly identified cancer causing protein,CIP2A, in human cancers. We identify new signaling pathways which involve some well established cancer causing genes like MYC. In addition to the mechanisms , we also demonstrate the clinical relevance, in the form of prognostic role, of CIP2A in human cancers for the first time

Cancerous Inhibitor of Protein Phosphatase 2A, an Emerging Human Oncoprotein and a Potential Cancer Therapy Target

Abstract Protein phosphatase 2A (PP2A) complexes function as tumor suppressors by inhibiting the activity of several critical oncogenic signaling pathways. Consequently, inhibition of the PP2A phosphatase activity is one of many prerequisites for the transformation of normal human cells into cancerous cells. However, mechanisms for PP2A inactivation in human cancers are poorly understood. The aberrant expression of cancerous inhibitor of protein phosphatase 2A (CIP2A), a recently identified endogenous PP2A inhibitor in malignant cells, is one such mechanism. Various independent studies have validated CIP2A's role in promoting tumor growth and resistance to apoptosis and senescence-inducing therapies. Notably, high CIP2A expression predicts poor patient prognosis in several human cancer types. Among the oncogenic proteins dephosphorylated by PP2A, the MYC oncoprotein, which is phosphorylated at serine 62, has surfaced as a marker for the oncogenic activity of CIP2A. The positive-feedback loop between CIP2A and MYC augments the activity of MYC in cancer cells. In addition, CIP2A promotes the phosphorylation and activity of additional oncoproteins, including E2F1 and AKT. However, CIP2A is not essential for normal mouse growth and development. These findings indicate that CIP2A is a novel anticancer target based on PP2A reactivation and inhibition of the oncogenic activity of its downstream effectors. The potential approaches and feasibility of targeting CIP2A are discussed here. Cancer Res; 73(22); 6548–53. ©2013 AACR.</jats:p

Abstract 4194: Constitutive DNA-damage signaling promotes cancer cell proliferation through Chk1-CIP2A pathway independent of ATM-ATR

Abstract DNA damage is a hallmark of malignantly transformed cells. Accordingly, overexpression of the DNA damage activated kinases has been observed in different human cancers. However, it is unclear whether constitutive DNA damage present in unperturbed cancer cells promotes tumourigenesis. Here we show that increased activity of DNA damage sensitive kinase Chk1 promotes proliferation of several cancer cell types by stimulating expression of CIP2A protein. Either chemical or genetic inhibition of Chk1, and not of ATM-ATR, results in potent inhibition of CIP2A protein expression levels. Importantly, Chk1 siRNA-elicited inhibition of cell proliferation and clonogenic growth is rescued by overexpression of CIP2A from a heterologous promoter. Moreover, in clinical (human) tumor samples there is a significant association between CIP2A and Chk1 expression in both ovarian and gastric cancers. Intriguingly, meta-analysis of seventeen published genome wide studies on different types of cancers unveils a striking similarity in the gene expression patterns of both CIP2A and Chk1. Amongst these, 12/17 studies show overexpression (top 10%) of both these proteins. Additionally, similarly to CIP2A, increased Chk1 expression is shown to correlate with tumor progression in human cancer. In summary, these results identify a novel function for DNA damage kinase Chk1 in regulation of the human oncoprotein CIP2A. In general, these results provide an unprecented molecular mechanism by which constitutive DNA damage present in cancer cells promotes tumourigenesis. Additionally, as CIP2A is not significantly expressed in most of the normal human tissues, it is proposed that targeting of CIP2A might abrogate the Chk1-mediated support of proliferation without concerns related to anticancer therapy directly targeting Chk1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4194. doi:10.1158/1538-7445.AM2011-4194</jats:p