Visit our Expo - Redox and Inflammation signaling 2012

Session X : Cell death in cancer Poster X, 78
Let’s flip the FLIP idea
Beata Pajak, Arkadiusz Orzechowski
Department of Physiological Sciences, Faculty of Veterinary Medicine, Warsaw
Agricultural University, Nowoursynowska 159, 02-776 Warsaw, Poland, e-mail:
bepaj@wp.pl
The resistance of cancer cells to elimination by death ligands (TNF-alpha, TRAIL, FasL) in
the extrinsic apoptotic pathway allows a variety of tumors to grow and develop. The
elucidation of the antiapoptotic mechanisms responsible for this phenomenon is the major
challenge of the contemporary medicine. The last decade revealed several strategies of cancer
cells (including colon adenocarcinomas) of how to avoid cell death and to maintain cell
survival. Colorectal cancer cells inhibit death ligand-induced apoptosis by the expression of
several antiapoptotic proteins, such as FLIP (FLICE-inhibitory protein), ,cIAPs (cellular
inhibitors of apoptosis), and others which inhibit either signal transduction or execution of
apoptosis. In colorectal cancer COLO 205 cell line the immunoprecipitation of FADD (Fasassociated
death domain-containing protein) showed its assembly with FLIP. Usually, the
presence of FLIP in the TNF-alpha signalosome inhibits the caspase 8 (FLICE - FADD-like
interleukin-1#-converting enzyme) autoactivation, and blocks TNF-alpha-induced apoptosis.
Several studies demonstrated that the reduction of FLIP level by the protein synthesis
inhibitors, such as cycloheximide or bis-indolylmaleimide could sensitize cells to apoptotic
stimuli. Similarly, actinomycin D, the inhibitor of DNA transcription exerts cell deathpromoting
properties. In COLO 205 cell line the Western-blot and immunocytochemistry
analyses demonstrated, that the use of cycloheximide decreases the FLIP protein level in a
time-dependent manner, what correlates positively with the progression of cell death. In
contrast, the use of siRNA-FLIP did not lead to cell death upon TNF-alpha treatment. It is
concluded that protein(s) other than FLIP inhibited TNF-alpha-dependent cell death
irrespective to the interaction of FLIP with the TNF-RI signalosome. Thus, unknown
antiapoptotic protein(s) blocked apoptosis downstream to the TNF-R1 signalosome. This
undefined protein(s) is essential for “immune escape” of COLO 205 cells. It is also assumed,
that susceptibility of colorectal cancer cells to TNF-alpha-induced cell death upon
concomitant cycloheximide treatment could be a consequence of oxidative stress and changes
in the intracellular milieu. The latter is currently under detailed scrutiny.
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