Walter
G. Hanel
1st
Year Graduate Student
Department:
Pathology
Graduate Program: Genetics
Advisor:
Ute Moll
Abstract (rotation):
Preceptor: Ute Moll, Department of Pathology, Stony Brook University
Title: Mechanism of anthrax lethal factor
inhibition by green tea products and antibiotics
P53
plays a pivotal role in induction of cell cycle arrest, DNA repair,
cellular senescence, and apoptosis in response to a variety of stimuli.
The p53 response is mediated not only by post-translational modifications
and protein stability, but also by the cellular localization to distinct
compartments, such as the nucleus, cytoplasm and mitochondria. This
localization depends on a variety of modifications such as phosphorylation
and ubiquitination which may be significantly altered in a number of
cancers. There is still much debate as to what mechanisms regulate the
nuclear accumulation of p53 in response to genotoxic stress. While the
CRM mediated nuclear export of p53 and its regulation have been extensively
studied, little is known about the mechanisms regulating p53 nuclear
import. By fractionation of a variety of human cancer cell lines, ubiquitinated
p53 was found to be mainly present in the cytoplasm, with very little
ubiquitinated p53 present in the nucleus. I found that the ratio of
Mdm2 to p53, a crucial determinant of p53 ubiquitination, is much higher
in the cytoplasm as compared to the nucleus. Import was found to be
dependent on binding of p53’s NLS lysine residues 319-321 to the
import adaptor, importin a3. Moreover, the NLS residues 319-321 were
found to be the targets of Mdm2-mediated ubiquitination, explaining
the mechanism of how ubiquitinated p53’s import is inhibited.
By siRNA knockdown of importin a3, I found a significantly attenutated
p53 accumulation in the nucleus both in untreated and in camptothecin
treated cells. In addition, transcription of p53 target p21 was also
significantly decreased after knockdown of importin a3. These results
led me to propose a new model, whereby enhanced import of p53 in response
to stress contributes significantly to nuclear accumulation of p53 and
thus defines a further mode of regulation of the p53 stress response.
Publications:
(MSTP-supported publications indicated with an *)
Kramer JM., Hanel W., Shen F., Isik N., Malone J.P.,
Maitra A., Sigurdson W., Swart D., Tocker J., Jin T., Gaffen SL. (2007).
Cutting Edge: Identification of a Pre-Ligand Assembly Domain (PLAD)
and Ligand Binding Site in the IL-17 Receptor. J Immunology.
179(10): 6379:83
Maitra
A., Shen F., Hanel W., Mossman K., Tocker J., Swart
D., Gaffen SL. (2007). Distinct functional motifs within the IL-17 receptor
regulate signal transduction and target gene expression. Proc
Natl Acad Sci. U.S.A. 104(18):7506-11
Tanner
MJ., Hanel W., Gaffen SL., Lin X. (2007). CARMA1 coiled-coil
domain is involved in the oligomerization and subcellular localization
of CARMA1 and is required for T-cell receptor-induced NF-kappaB activation.
J Biol Chem. 282(23):17141-7
