Cytoplasmic p21 expression levels determine cisplatin resistance in human testicular cancer
Roelof Koster, Alessandra di Pietro, Hetty Timmer-Bosscha, Johan H. Gibcus, Anke van den Berg, Albert J. Suurmeijer, Rainer Bischoff, Jourik A. Gietema, Steven de Jong
Roelof Koster, Alessandra di Pietro, Hetty Timmer-Bosscha, Johan H. Gibcus, Anke van den Berg, Albert J. Suurmeijer, Rainer Bischoff, Jourik A. Gietema, Steven de Jong
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Research Article Oncology

Cytoplasmic p21 expression levels determine cisplatin resistance in human testicular cancer

Abstract

Platinum-based chemotherapies such as cisplatin are used as first-line treatment for many cancers. Although there is often a high initial responsiveness, the majority of patients eventually relapse with platinum-resistant disease. For example, a subset of testicular cancer patients still die even though testicular cancer is considered a paradigm of cisplatin-sensitive solid tumors, but the mechanisms of chemoresistance remain elusive. Here, we have shown that one key determinant of cisplatin-resistance in testicular embryonal carcinoma (EC) is high cytoplasmic expression of the cyclin-dependent kinase (CDK) inhibitor p21. The EC component of the majority of refractory testicular cancer patients exhibited high cytoplasmic p21 expression, which protected EC cell lines against cisplatin-induced apoptosis via CDK2 inhibition. Localization of p21 in the cytoplasm was critical for cisplatin resistance, since relocalization of p21 to the nucleus by Akt inhibition sensitized EC cell lines to cisplatin. We also demonstrated in EC cell lines and human tumor tissue that high cytoplasmic p21 expression and cisplatin resistance of EC were inversely associated with the expression of Oct4 and miR-106b seed family members. Thus, targeting cytoplasmic p21, including by modulation of the Oct4/miR-106b/p21 pathway, may offer new strategies for the treatment of chemoresistant testicular and other types of cancer.

Authors

Roelof Koster, Alessandra di Pietro, Hetty Timmer-Bosscha, Johan H. Gibcus, Anke van den Berg, Albert J. Suurmeijer, Rainer Bischoff, Jourik A. Gietema, Steven de Jong

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Figure 1

High cytoplasmic p21 expression is associated with cisplatin resistance in EC cell lines.

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High cytoplasmic p21 expression is associated with cisplatin resistance ...
(A) Survival of EC cells after 96 hours of continuous cisplatin treatment as indicated. (B) Differences in p21 and p53 levels of the EC cell lines treated and untreated with cisplatin for 24 hours as indicated. A representative example of 3 independent experiments is shown. (C) Differences in CDKN1A expression levels of the EC cell lines, treated and untreated. Note that the intrinsic cisplatin-resistant EC cell lines (2102EP and Scha) have higher basal and cisplatin-induced p21/CDKN1A levels compared with cisplatin-sensitive EC cell lines (Tera and 833KE). (D) p21 is localized in the cytoplasm in EC cells when untreated and after 24 hours of cisplatin treatment. Hoechst staining was used to visualize nuclei (blue). Scale bar: 30 μm. (E) 24 hours after cisplatin (CP) treatment or γ irradiation (IR), nuclear and cytoplasmic proteins were isolated and analyzed by WB for expression of p21 using retinoblastoma protein (pRB) as nuclear control, whereas β-actin is shown as a loading control. WB of total lysates shows that, despite an almost similar p53 increase, γ irradiation in contrast with cisplatin treatment strongly induced accumulation of p21 both in cisplatin-resistant Scha and cisplatin-sensitive Tera cells. Representative examples of 3 independent experiments are shown. Data are represented as mean ± SD.