Visit our Expo - Redox and Inflammation signaling 2012

Session XVII : Cell signaling in health and disease Poster XVII, 39
Mechanisms of selenium cytotoxicity in a malignant mesothelioma model – targeting
Thioredoxin Reductase-1
Gustav Nilsonne, Branka Kocic, Aristi Potamitou Fernandes, Agnes Stein, Anna-Klara
Rundlöf, Mikael Björnstedt, Anders Hjerpe, and Katalin Dobra.
All authors: Karolinska Institutet, Institution for Laboratory Medicine, Dept. of
Pathology. Karolinska Univ Hosp Huddinge F-46, S-141 86 Huddinge, Sweden.
Malignant mesothelioma (MM) is an aggressive tumour arising from the serous cavities. MM
cells may differentiate into an epithelioid or a sarcomatoid phenotype, and the latter is more
chemoresistant and associated with a worse prognosis. The thioredoxin (Trx) system is
upregulated in many tumors, and the highest reported levels have been found in MM. The
system comprises Trx, Thioredoxin Reductase (TrxR1) and NADPH. It functions mainly to
maintain intracellular redox balance, but also counteracts apoptosis. Sodium selenite causes
oxidative stress.
The objectives of this study were to investigate whether selenite could induce apoptosis in a
sarcomatoid and an epithelioid MM cell line, and what mechanisms would mediate the
cytotoxic effects.
Apoptosis was measured by three independent methods and was induced in the sarcomatoid
cell line at low concentrations. The IC 50 was 7,5 µM. IC 50 of the epithelioid cell line, with
greater expression of the Trx system, was 21 µM. The DCF probe revealed ROS formation
following selenite treatment, analysed with confocal microscopy. Selenite concentrations of
10 µM or more inhibited TrxR1 effectively.
ICC revealed p53 activation in both cell lines. Immunostaining with FACS analysis revealed
that Bax was activated by selenite. The DioC6 marker analysed by FACS showed loss of
mitochondrial membrane potential. Inhibition of JNK using SP600125 had no effect in either
cell line. Inhibition of p38 decreased the activation of Bax. No caspase activity was detected
after selenite treatment. The pan-caspase inhibitor z-VAD-fmk did not attenuate apoptosis.
In conclusion, selenite generated ROS, inhibited TrxR1 and caused apoptosis in two MM cell
lines. The therapy resistant sarcomatoid cells were more sensitive. The effects were mediated
through p53 and Bax, but appear to be independent of both caspases and JNK. This is a
promising new treatment option for an aggressive and chemoresistant tumor.
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