CIP2A is overexpressed and involved in the pathogenesis of chronic myelocytic leukemia by interacting with breakpoint cluster region-Abelson leukemia virus

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.

Investigation of the Effect of Imatinib and Hydroxyurea Combination Therapy on Hematological Parameters and Gene Expression in Chronic Myeloid Leukemia (CML) Patients

(1) Background: Chronic myeloid leukemia is defined as the neoplastic development of mostly myeloid cells in the bone marrow. Several treatments, including chemotherapy, radiation, hormone treatment, and immunological therapy, can be used to control this condition. The therapeutic impact on leukemic individuals varies, and the response to therapy varies between patients due to disease heterogeneity. The primary goal of this study is to compare the effects of single and Imatinib (IM) and Hydroxyurea (HU) combined treatment on hematological parameters and gene expression in CML patients. (2) Methods: This study was conducted on 51 patients, with chronic myeloid leukemia, who were admitted to Al-Basher hospital in Amman, Jordan, for follow-up. Their hematological parameters were checked and gene expression was measured for (BCL2, PP2A, CIP2A, and WT1). (3) Results: The BCL2 gene was found to be less expressed in both IM and (HU + IM) treatments as compared to the HU group alone, while PP2A gene expression was raised. Such a thing indicates that the outcome of the combined therapy method is not ideal, since PP2A activation causes CML cells to move toward the blast crisis stage. Furthermore, CIP2A gene expression revealed that IM and (HU + IM) had the same therapeutic effect and were more successful in CML patients than HU alone. With regards to the treatment effect on hematological parameters, notably in CML patients in later stages, the combination therapy (HU + IM) raised lymphocyte count, indicating a greater response to the treatment. When compared to single medicines, the combination treatment reduced the proportion of neutrophils to normal reference ranges. Platelet counts, on the other hand, dramatically decreased in both IM and (HU + IM). (4) Conclusion: Because the studied genes (BCL2, PP2A, CIP2A, and WT1) are participating in cell proliferation and death, the findings show that the examined genes are significant to understand the efficacy of various therapies. Furthermore, it was found that there was a clear effect of the clinic-based strategic treatment on hematological indicators such as WBCs, lymphocytes, neutrophils, and platelet counts.

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.

Potential anti-tumor effects of FTY720 associated with PP2A activation: a brief review

FTY720 (Fingolimod, Gilenya (†) ) is an FDA-approved immunosuppressant currently used in the treatment of multiple sclerosis. However, a large number of studies over the last few years have shown that FTY720 shows potent antitumor properties that suggest its potential usefulness as a novel anticancer agent. Interestingly, the restoration of protein phosphatase 2A (PP2A) activity mediated by FTY720 could play a key role in its antitumor effects. Taking into account that PP2A inactivation is a common event that determines poor outcome in several tumor types, FTY720 could serve as an alternative therapeutic strategy for cancer patients with such alterations.

Leucine-rich repeat-containing protein 59 mediates nuclear import of cancerous inhibitor of PP2A in prostate cancer cells

Using yeast two-hybrid analysis, we identified several novel protein interactions for the oncoprotein Cancerous Inhibitor of PP2A (CIP2A) and confirmed a subset of these interactions in human cancer cell lines. Analysis of the interaction in prostate carcinoma cells between CIP2A and leucine-rich repeat-containing protein 59 (LRRC59) suggests that CIP2A is translocated into the nucleus at G2/M through its association with LRRC59. Recent work by others has demonstrated that nuclear CIP2A disrupts mitotic checkpoints, which promotes deregulation of the cell cycle and increases cancerous phenotypes. Thus, we provide a novel therapeutic mechanism for inhibiting CIP2A function in cancerous cells via targeting the CIP2A-LRRC59 interaction.

The Basic Biology of PP2A in Hematologic Cells and Malignancies

Reversible protein phosphorylation plays a crucial role in regulating cell signaling. In normal cells, phosphoregulation is tightly controlled by a network of protein kinases counterbalanced by several protein phosphatases. Deregulation of this delicate balance is widely recognized as a central mechanism by which cells escape external and internal self-limiting signals, eventually resulting in malignant transformation. A large fraction of hematologic malignancies is characterized by constitutive or unrestrained activation of oncogenic kinases. This is in part achieved by activating mutations, chromosomal rearrangements, or constitutive activation of upstream kinase regulators, in part by inactivation of their anti-oncogenic phosphatase counterparts. Protein phosphatase 2A (PP2A) represents a large family of cellular serine/threonine phosphatases with suspected tumor suppressive functions. In this review, we highlight our current knowledge about the complex structure and biology of these phosphatases in hematologic cells, thereby providing the rationale behind their diverse signaling functions. Eventually, this basic knowledge is a key to truly understand the tumor suppressive role of PP2A in leukemogenesis and to allow further rational development of therapeutic strategies targeting PP2A.