P53 Hypersensitivity Is the Predominant Mechanism of the Unique Responsiveness of Testicular Germ Cell Tumor (TGCT) Cells to Cisplatin

Matthias Gutekunst,Andrea Weilbacher,Moshe Oren,Christiane Markwardt,Jürgen Thomale,Walter E. Aulitzky,Michael A. Dengler,Heiko van der Kuip,Andrei L. Gartel

doi:10.1371/journal.pone.0019198

Abstract

Consistent with the excellent clinical results in testicular germ cell tumors (TGCT), most cell lines derived from this cancer show an exquisite sensitivity to Cisplatin. It is well accepted that the high susceptibility of TGCT cells to apoptosis plays a central role in this hypersensitive phenotype. The role of the tumor suppressor p53 in this response, however, remains controversial. Here we show that siRNA-mediated silencing of p53 is sufficient to completely abrogate hypersensitivity not only to Cisplatin but also to non-genotoxic inducers of p53 such as the Mdm2 antagonist Nutlin-3 and the proteasome inhibitor Bortezomib. The close relationship between p53 protein levels and induction of apoptosis is lost upon short-term differentiation, indicating that this predominant pro-apoptotic function of p53 is unique in pluripotent embryonal carcinoma (EC) cells. RNA interference experiments as well as microarray analysis demonstrated a central role of the pro-apoptotic p53 target gene NOXA in the p53-dependent apoptotic response of these cells. In conclusion, our data indicate that the hypersensitivity of TGCT cells is a result of their unique sensitivity to p53 activation. Furthermore, in the very specific cellular context of germ cell-derived pluripotent EC cells, p53 function appears to be limited to induction of apoptosis.

Highlights

testicular germ cell tumors (TGCT) develop from pre-malignant intratubular germ cell neoplasias and can be histologically classified into seminomas and non-seminomas
Hypersensitivity of embryonal carcinoma (EC) cells to Cisplatin is p53-dependent Most cell lines derived from EC undergo apoptosis upon exposure to very low concentrations of Cisplatin
In TGCT cells we found a tight p53 siRNA dose response relationship for the rescue from Cisplatin-induced apoptosis, demonstrating that in these cells the amount of p53 protein is pivotal for their sensitivity to Cisplatin (Figure 1B)

Summary

Introduction

TGCT develop from pre-malignant intratubular germ cell neoplasias and can be histologically classified into seminomas and non-seminomas. Dependent on the histological type, non-seminomas are composed of a disorganized mixture of differentiated somatic cell types and extraembryonic cells, together with EC cells. In contrast to most other solid malignancies, TGCT can be cured at a rate in excess of 80% by Cisplatin-based chemotherapy regimens even in advanced metastasized phases [2,3]. These unique response rates have been linked to an intrinsic hypersensitivity to DNA damaging agents, as observed in several human EC lines derived from TGCT [4,5]. Various attempts have been made to understand the molecular mechanisms behind this hypersensitivity, mostly by comparing Cisplatin-sensitive TGCT cell lines with Cisplatin-resistant clones established from the same origin by continuous treatment with increasing doses of Cisplatin

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Conclusion