Visit our Expo - Redox and Inflammation signaling 2012

Session X : Cell death in cancer Poster X, 64
The effect on cell death in drug and CD95-mediated apoptosis by the apoptosis enhancer
Daxx in renal cell carcinoma
C Mahotka, N Wethkamp, P Reinecke, and HE Gabbert
Institute of Pathology, Heinrich Heine-University, Duesseldorf, Germany; e-mail:
mahotka@med.uni-duesseldorf.de
Introduction: Deregulation of apoptosis is involved in the development of cancer. Expression
of Daxx is implicated in apoptosis but whether its function is pro- or anti-apoptotic is still
discussed controversial. Daxx is involved in the regulation of p53 dependent transcription and
associates with the promyelocytic leukemia protein (PML) in speckled subnuclear structures
so called PML oncogenic domains (PODs). Overexpression-based experiments in renal cell
carcinoma (RCC) were used to explore the impact of Daxx on the CD95-dependent apoptosis
and cell death induced by different anticancer agents such as Etoposide, Topotecan, Taxol and
Doxorubicine. Results: 1. Constitutive overexpression of Daxx in the CD95-ligand sensitive
human RCC cell line clearCa-6 (clear-Ca-6/GFP-Daxx) has no influence on cell growth. 2.
Treatment of clearCa-6/GFP-Daxx with the CD95-receptor agonistic antibody CH11 leads to
no further enhancement of the CD95-dependent apoptosis compared to control cell line clear-
Ca-6/GFP as analyzed by MTT Assay and Caspase-8 and PARP Western Blot, respectively.
3. Daxx overexpression in the CD95-ligand resistent RCC cell line clearCa-2 (clearCa-2/GFP-
Daxx) also causes no sensitization to the CD95-dependent apoptosis. 4. Although Daxx is
known to trigger CD95-mediated apoptosis via the activation of JNK by a Caspase-8
independent mechanism, even under Caspase-8 inhibition no Daxx-mediated modulation of
the CD95-mediated apoptosis was detectable and moreover, no differences in CD95-mediated
JNK aktivation were obvious as shown by in vitro kinase assays. 5. Treatment of both GFP-
Daxx transduced cell lines with various anticancer drugs points to a protective role of Daxx
during Taxol-dependent apoptosis of clearCa-2/GFP-Daxx, which is probably mediated by an
enhanced activation of the p38/JNK pathway as shown by in vitro kinase assays.
Conclusions: Our study suggests that the CD95-mediated apoptosis in renal cell carcinoma is
not effected by the overexpression of the apoptosis enhancer Daxx. In contrast, the data
indicate a rather anti-apoptotic than pro-apoptotic role for Daxx in human RCC as shown by
the Daxx overexpression-mediated protective effect during Taxol-dependent apoptosis in the
RCC cell line clearCa-2.
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