Visit our Expo - Redox and Inflammation signaling 2012

Session X : Cell death in cancer Poster X, 55
Forced expression of the novel heat shock protein H11 triggers cancer cell apoptosis
through TAK1 activation providing a molecular target for cancer therapy
Jennifer Laing, Baiquan Li, Cynthia Smith, and Laure Aurelian.
Pharmacology and Experimental Therapeutics, University of Maryland School of
Medicine, Baltimore, MD, 21201, U.S.A. E-mail: laurelia@umaryland.edu
H11 is a small heat shock protein (Hsp) recently cloned in our laboratory. It retains the alphacrystallin
motif, but differs from canonical family members in that its expression is inhibited
in some cancer cells (notably melanoma, prostate and breast) relative to matched normal
tissues. Inhibition is by aberrant DNA methylation, and can be forced by treatment with
demethylating agents. The current studies were designed to examine the role of H11 overload
in tumor cell fate determination. Melanoma was used as a model, because it is a prevalent
cancer, which is resistant to most types of chemotherapy. To control specificity of gene
upregulation, human melanoma cells were stably transfected with a retrovirus that expresses
H11 under the control of a tetracycline inducible promoter. They were examined for H11
expression and apoptosis at 1-3 days after doxycycline (Dox) treatment. H11 was rapidly (1
day) expressed and expression was associated with activation (cleavage) of caspases-9 and -3
and p38MAPK, as well as a significant increase in the % TUNEL+ cells.
Immunopercipitation/immunoblotting assays indicated that H11, but not its apoptosis
dominant negative mutant W51C, binds TAK1 resulting in the activation of its kinase activity
(determined by immunocomplex PK assays with MKK6 as the phosphorylation substrate).
Activated TAK1, in turn, activates p38MAPK, which is responsible for caspase-3 cleavage, as
evidenced by inhibition with the TAK1 dominant negative mutant K63Wor the
pharmacologic inhibitor SB203580. In addition, the H11-TAK1 complex binds and
phosphorylates #-catenin, thereby inhibiting its transcriptional activity and resulting in the
inhibition of MITF and CDK2, both of which are required for melanoma cell proliferation.
Preliminary data using animal xenograft models indicate that H11 overload inhibits tumor cell
growth and triggers apoptosis, also in vivo. The data indicate that modulation of signaling
pathways by H11 overload is a promising novel paradigm for cancer therapy.
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