Julia Louise Harris Behnfeldt Dissertation Defense Booklet

THE OHIO STATE UNIVERSITY
BIOMEDICAL SCIENCES
GRADUATE PROGRAM
SPRING 2015
Julia Louise Harris Behnfeldt
PhD Candidate
“CHK2 phosphorylation of the BLM helicase
promotes its interaction with topoisomerase IIα and
the resolution of chromosome breakage.”
04/10/2015
James Cancer Hospital B030
2:00PM
VITA
September 7, 1987 . . . . . . . . . . . . . . . . . . . . .Born – Napoleon, OH
May 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.A. Biology
Capital University
July 2010 . . . . . . . . . . . . . . . . . . . . . . . . . PhD Biomedical Student
The Ohio State University
COMMITTEE MEMBERS
Joanna Groden, Advisor, PhD
Dawn Chandler PhD
Jeffrey Parvin MD, PhD
Kay Huebner PhD
ABSTRACT
Genomic instability, including chromosome breakage, can
arise from dysfunctional cell cycle control, environmental agents
that damage DNA or ineffective DNA repair; it’s a hallmark of
most cancers. The induction or regulation of genomic instability
also represents an opportunity in cancer therapeutics.
The BLM helicase is a RecQ-like helicase with DNA repair
functions in homologous recombination and DNA replication.
Cells lacking BLM exhibit a hyper-recombination phenotype,
increased chromosome breakage and the inability to repair some
types of DNA damaged. Previous work has shown that the
interaction of topoisomerase IIα (TOP2A) and BLM is required to
stimulate BLM helicase activity and resolve chromosome breaks.
This works shows that phosphatase-treatment of BLM inhibits
topoisomerase IIα stimulation of BLM helicase activity, although
the specific activity of BLM is increased. Computational analysis
identified two putative serine clusters S517, S518 (C1) and S577,
S579, S580 (C2) within the topoisomerase IIα interaction domain
of BLM. Mutagenesis of these clustered serines to alanine
(BLMC1A, BLMC2A) or aspartate (BLMC1D, BLMC2D)
permitted testing of their ability to regulate the
BLM/topoisomerase IIα interaction and function in chromosome
breakage. BLMC2A was unable to lower high micronuclei
numbers in cells lacking endogenous BLM, while BLMC1A,
BLMC1D, BLMC2D and wild-type BLM lowered the high
micronuclei numbers. All six single amino acid mutants behaved
similar to wild-type BLM.
In localization studies, BLMC2A displayed a 2.5-fold
decrease in colocalization with topoisomerase IIα during G2/Mphase, while also exhibiting a 2.5-fold increase in the number of
anaphase ultra-fine bridges (UFBs). In vitro phosphorylation of
BLM by CHK2 restored the topoisomerase IIα-stimulation of
phosphatased-BLM in contrast to treatment with CHK1. Lastly,
transfection of BLMC2D into BLM-/- cells exhibited lower
amounts of DNA double-strand breaks (DSBs) compared to wildtype BLM and BLMC2A following inhibition of CHK2 in vivo.
These findings demonstrate that post-translational
modification of BLM by CHK2 at amino acids S577, S579 and
S580 controls its interaction with topoisomerase IIα, most likely at
the G2-M boundary, and its functions in regulating chromosome
breakage. They also suggest that disruption of BLM
phosphorylation
via
CHK2
inhibitors
to
control
BLM/topoisomerase IIα localization and/or interaction may be a
novel mechanism to manipulate DNA damage.
RECENT ABSTRACTS AND PRESENTATION
“CHK2 phosphorylation of BLM helicase promotes its interactions
with topoisomerase IIα and resolution of chromosome breakage.”
2014 Gordon Research Conference. Newry, ME. Invited Poster
“Interaction of the BLM helicase and topoisomerase IIα is
regulated by BLM phosphorylation.” 2014 Council of Graduate
Students Hayes Research Forum. Columbus, OH. Invited Speaker
“Interaction of the BLM helicase and topoisomerase IIα is
regulated by BLM phosphorylation.” 2013 OSU Comprehensive
Cancer Center Annual Meeting. Columbus, OH. Poster
“Thermal stability assay for glaucoma-causing myocilin mutants
using maltose binding fusion protein (MBP) and method to screen
for small molecule stabilizers.” 2010 American Society for
Biochemistry and Molecular Biology (ASBMB) Meeting.
Anaheim, CA. Poster
“Rescue of glaucoma-causing mutant myocilin thermal stability by
chemical chaperones.” 2010 Capital University Undergraduate
Symposium. Bexley, OH. Invited Speaker
“Thermal stability assay for glaucoma-causing myocilin mutants
using maltose binding fusion protein (MBP) and method to screen
for small molecule stabilizers.” 2009 Georgia Institute of
Technology Structural Biology and Molecular Biophysics
Symposium. Atlanta, GA. Poster
“Structure and function of a sno-like RNA in Haloferax volcanii.”
2009 American Society for Biochemistry and Molecular Biology
(ASBMB) Meeting. New Orleans, LA. Invited Speaker
RECENT PUBLICATIONS
Harris Behnfeldt J, Acharya S, Keirsey J, Tangeman L, Gocha
ARS, German J, Groden J. The BLM helicase/TOP2A interaction
is regulated by CHK2 to resolve chromosome breakage.
Submitted. 2015.
Acharya S, Kaul Z, Gocha ARS, Martinez A, Harris J, Parvin J,
Groden J. Association of BLM and BRCA1 during telomere
maintenance in ALT cells. Plos One. 2014, 9(8):e103819.
Gocha ARS, Harris J, and Groden J. Alternative lengthening of
telomeres: Permissive mutations, DNA repair proteins, and
tumorigenic progression in mammalian cells. Mut Res. 2012, 743744.
Burns JN, Orwig SD, Harris JL, Watkins JD, Vollrath D,
Lieberman RL. Rescue of glaucoma-causing mutant myocilin
thermal stability by chemical chaperones. ACS Chem Biol. 2010,
477-487.
AWARDS AND HONORS
2015 American Institute of Biological Sciences Emerging Public
Policy Leadership Award Honorable Mention
2015 Presidential Management Fellowship (PMF) Semi-Finalist
2014 OSU Pelotonia Fellowship
2013 OSU Art of Cancer Research − 2nd place
2011 National Science Foundation Graduate Research Fellowship
(NSF-GRFP)
2010 NSF-GRFP Honorable Mention
2010 OSU University Fellowship
FUTURE PLANS
I will use my scientific training to pursue a career in science policy
and advocacy.
Biomedical Sciences Graduate Program
1170 Graves Hall
333 W. 10th Avenue
Columbus, Ohio 43210
www.ibgp.org