Selective enhancing effect of early mitotic inhibitor 1 (Emi1) depletion on the sensitivity of doxorubicin or X-ray treatment in human cancer cells.

J Biol Chem. 2013 Jun 14;288(24):17238-52.

Shimizu N, Nakajima NI, Tsunematsu T, Ogawa I, Kawai H, Hirayama R, Fujimori A, Yamada A, Okayasu R, Ishimaru N, Takata T, Kudo Y.

Department of Oral and Maxillofacial Pathobiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan.

PMID: 23645673

 

Abstract:

Chemotherapy and radiation in addition to surgery has proven useful in a number of different cancer types, but the effectiveness in normal tissue cannot be avoided in these therapies. To improve the effectiveness of these therapies selectively in cancer tissue is important for avoiding side effects. Early mitotic inhibitor 1 (Emi1) is known to have the function to inhibit anaphase-promoting complex/cyclosome ubiquitin ligase complex, which ubiquitylates the cell cycle-related proteins. It recently has been shown that Emi1 knockdown prevents transition from S to G2 phase by down-regulating geminin via anaphase-promoting complex/cyclosome (APC/C) activation. At present, anticancer drugs for targeting DNA synthesis to interfere with rapidly dividing cells commonly are used. As Emi1 depletion interferes with completion of DNA synthesis in cancer cells, we thought that Emi1 knockdown might enhance the sensitivity for anticancer agents. Here, we confirmed that Emi1 siRNA induced polyploidy for preventing transition from S to G2 phase in several cancer cell lines. Then, we treated Emi1 depleted cells with doxorubicin. Interestingly, increased apoptotic cells were observed after doxorubicin treatment in Emi1 siRNA-treated cancer cells. In addition, Emi1 depletion enhanced the sensitivity of x-ray irradiation in cancer cells. Importantly, synergistic effect of Emi1 knockdown in these combination therapies was not observed in normal cells. These results suggest that Emi1 siRNA can be a useful tool for enhancing of sensitivity of cancer cells to anticancer reagents and radiation.

KEYWORDS: Anticancer Drug, Cancer, Cancer Therapy, Cell Cycle, DNA Damage, DNA Synthesis, Radiation Biology

 

Supplement:

Cancer can be treated by various means such as surgery, chemotherapy, radiation therapy, immunotherapy, and monoclonal antibody therapy. Chemotherapy alone or in combination with other treatments such as surgery or radiation has proven useful in a number of different cancer types, but the effectiveness of chemotherapy is often limited by the toxicity to non-targeted tissues in the body. The choice of therapy depends upon the location and grade of the tumor and the stage of the disease, as well as the physical condition of the patient. Complete inactivation of the cancer without damage to the rest of the body is the goal of treatment. The majority of chemotherapeutic drugs affect cell division or DNA synthesis and act by killing cells that divide rapidly, one of the main properties of most cancer cells. Anticancer agents also harm cells that divide rapidly under normal circumstances: cells in the bone marrow, digestive tracts, and hair follicles. These effects result in the common side-effects of chemotherapy including myelosuppression, mucositis and alopecia. Recently, newer anticancer drugs including monoclonal antibodies and the new tyrosine kinase inhibitors are expected to be more effective than traditional anticancer drugs. At present, however, many traditional anticancer drugs for targeting DNA synthesis to interfere with rapidly dividing cells are commonly used. Radiation therapy is the medical application of ionizing radiation to suppressing tumor growth. Ionizing radiation works by damaging DNA to control tumor cell growth/division, but the effect of radiation in normal tissues cannot be avoided in these therapies.

Emi1 was identified as a factor inhibiting the function of APC/CCdh1. An abnormally high expression of Emi1 protein can be observed in various cancers. It recently has been reported that Emi1 depletion induces rereplication by decreased geminin via APC/C-mediated proteolysis. In addition, Emi1 depletion induces DNA damage, likely explained by replication stress upon deregulated Cyclin E- and A-associated kinase activities. Therefore, the finding that Emi1 depletion induced rereplication and DNA damage made us hypothesize that Emi1 knockdown might enhance the sensitivity of anticancer drugs and ionizing radiation. Interestingly, in this study, we demonstrated that Emi1 knockdown by using siRNA enhanced the sensitivity of anticancer reagents treatment (doxorubicin, camptothecin and etoposide) in cancer cells. Moreover, Emi1 siRNA enhanced the sensitivity of anticancer drugs under hypoxia condition that is recently shown to induce multidrug resistance. Similar synergistic effect of Emi1 knockdown in combination with ionizing radiation was observed. Importantly, no effect of Emi1 knockdown and no synergistic effect of Emi1 knockdown in combination with doxorubicin treatment and radiation in normal cells are useful findings for clinical application. We think that the inhibition of Emi1 function for induction of rereplication can be a novel strategy for enhancing sensitivity of cancer cells to chemotherapeutic drugs and ionizing radiation. This strategy may ease the burden of patients by reduction of the side effects.

Yasusei Kudo-fig new

Acknowledgments: This work was supported in part by JSPS KAKENHI Grant Number 23689074 and 25670778 (to Y. K.), Number 21249088 (to T. Ta.), Number 23390301, 24249067 (R. O.), Grant-in Aid for Cancer Research (19-9, H23-A-43) from MEXT (R. O.), and by a Research Fellowship for Young Scientists from the Japan Society for the Promotion of Science (no.23-6562) (to T. Ts.).

Contact: Department of Oral Molecular Pathology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, 3-18-15 Kuramoto, Tokushima 770-8504, Japan. Fax: +81-88-633-7328, E-mail: yasusei@tokushima-u.ac.jp

 

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