SUNDAY, DECEMBER 4- Late Abstracts 1 - Molecular Biology of the ...

SUNDAY
2035
Inhibition of Notch1 signaling by APP intracellular domain.
E-J. Ann 1 , J-H. Yoon 1 , J-S. Ahn 1 , H-S. Park 1 ; 1 Chonnam National University, Gwangju, Korea
The Notch1 receptor is a crucial controller of cell fate decisions, and is also a key regulator of
cell growth and differentiation in a variety of contexts. In this study, we have demonstrated that
the APP intracellular domain (AICD) attenuates Notch1 signaling by accelerated degradation of
the Notch1 intracellular domain (Notch1-IC) and RBP-Jk, through different degradation
pathways. AICD suppresses Notch1 transcriptional activity by the dissociation of the Notch1-IC–
RBP-Jk complex after processing by gamma-secretase. Notch1-IC is capable of forming a
trimeric complex with Fbw7 and AICD, and AICD enhances the protein degradation of Notch1-
IC through an Fbw7-dependent proteasomal pathway. AICD downregulates the levels of RBP-
Jk protein through the lysosomal pathway. AICD-mediated degradation is involved in the
preferential degradation of non-phosphorylated RBP-Jk. Collectively, our results demonstrate
that AICD functions as a negative regulator in Notch1 signaling through the promotion of
Notch1-IC and RBP-Jk protein degradation.
2036
Isoprenylcysteine methylation is required for growth and endocytosis in Dictyostelium
discoideum.
K. J. McQuade 1 , J. Bollan 1 , K. Bailey 1 , J. Fritz 1 ; 1 Colorado Mesa University, Grand Junction, CO
Many members of the Ras superfamily of small monomeric GTPases and other membraneassociated
proteins ending in carboxy-terminal –CAAX motifs are proteolytically processed and
reversibly methylated on isoprenylated terminal cysteine residues. Methylation is thought to
regulate localization and activity of these proteins. Ras GTPases are often overactive in cancer
cells and inhibitors of isoprenylcysteine methyltransferase are being tested as potential
chemotherapies, but the cellular effects of these inhibitors are unclear. We are characterizing
the effects of loss of isoprenylcysteine methyltransferase activity in the social amoeba,
Dictyostelium discodeum. Amoebae lacking methyltransferase activity grow slowly on bacterial
lawns and do not grow in shaking or adherent axenic culture. Methyltransferase-deficient cells
also migrate slowly towards folate, have reduced rates of endocytosis and are sensitive to
osmotic shock. The mechanisms underlying these defects are being investigated.
2037
Understanding the cellular function of poly(ADP-ribose) and its importance in cancer.
K. Krukenberg 1 , T. Mitchison 2 ; 1 Systems Biology, Harvard Medical School, Boston, MA,
2 Systems Biology, Harvard Medical School
Poly(ADP-ribose) is a unique but poorly understood post-translational modification. It has been
implicated in multiple cellular processes including DNA damage, cell death, inflammation,
protein stability and cell division. In the clinic, inhibition of poly(ADP-ribose) formation is showing
promise as a cancer therapeutic. Poly(ADP-ribose) polymerases (PARPs) catalyze the addition
of ADP-ribose onto acceptor proteins using NAD+ as a substrate. Though the importance of
PARPs and poly(ADP-ribose) is clear, their biological functions are not well understood. We are
working on developing tools for characterizing the function of PARPs and poly(ADP-ribose) and
are using these tools to further identify and define the biological roles of these intriguing and
essential molecules. Here we describe an assay for quantifying the levels of poly(ADP-ribose) in
cells that has increased sensitivity as compared to previous approaches. Using this assay, we
quantified the extent to which poly(ADP-ribose) levels vary throughout the cell cycle. We have
also found that different cancer cell types have different amounts of poly(ADP-ribose) and these