YSM Issue 90.5

genetics
FOCUS
Solving the Mystery
BRCA1 has been a mystery for so long
in part because the protein encoded by the
BRCA1 gene is large and complex—with
many components that make it difficult to
work with when trying to avoid denaturing.
The first main challenge in their research was
purifying the protein itself. Proteins, in comparison
with other macromolecules such as
carbohydrates, are much more unstable due
to their various components and ability to
denature, or become inactive, in suboptimal
conditions. Sung says it took several years
of experience to finally design a method to
not only express a very large protein but also
work with the proteins without rendering it
inactive. The researchers working with the
protein had to work quickly and gently with
the delicate proteins in a room with a controlled
temperature in order to preserve the
proteins in their functioning state. Leaving
the protein in a high or low temperature environment
or leaving it out for longer than
about half an hour could denature it to the
point where it could no longer be studied.
Their novel approach allowed them to express
thousand-fold the amount of protein
that was previously possible.
After overcoming this obstacle, the team
was set on further studying the proteins. But
there was still one missing piece to the puzzle
– the BRCA-BARD1 complex required a
helping hand in performing their DNA repair
task.
The team hypothesized that the BRCA1-
BARD1 complex works with an enzyme
called Rad51 because they observed certain
properties in protein factors that suggested
a cooperation with Rad51. To test their
hypothesis, they purposely induced DNA
damage in BRCA1 and then placed purified
elements in a test tube to determine whether
the DNA repair system worked. If the DNA
repair mechanism was successful, then that
proved their hypothesis that Rad51 indeed
was the enzyme that cooperated with the
complex to carry out DNA repair.
They were able to conclude that Rad51
recognized the damaged DNA and paired
it up with an undamaged molecule of DNA
to initiate the DNA repair reaction. Furthermore,
the BRCA1-BARD1 complex is essential
to the DNA repair reaction—when the
complex was unable to form, the repair did
not take place, and mutations affecting either
BRCA1 or BARD1 decreased the effectiveness
of repair.
IMAGE COURTESY OF SUNG LAB
►Dr. Patrick Sung (right), and associate
researcher Dr. Youngho Kwon (left).
Cancer Treatment’s Bright Future
Patrick Sung said that his passion for research
originated in his intellectual curiosity
and realization as a college student that
cancer was a huge problem that needed to
be cured. His ultimate goal is to develop
drugs that target specific known pathways
to treat cancer, and despite the large strides
this recent paper represents in the field, his
work is far from done. After the discovery
of the cooperation between BRCA1,
BARD1, and the Rad51 enzyme, it still remains
a question how BRCA1 and BRCA2
function together. BRCA2 is also a part of
the complex and plays a definite role in the
DNA repair mechanism as well, but it is not
as clearly understood as BRCA1. With their
novel approach to successful protein purification,
these researchers hope to reconstitute
the larger complex including BRCA2
and determine its relation to cancer formation.
Moreover, they are interested in understanding
how mutations work so that
they can find a basis for using compounds
in cancer treatment.
While many questions remain targets of
Sung’s continued research, it is likely that
both the biological discovery and technical
contribution to the protein purification
process will lead to progress in treating
cancers. Now that researchers know how
the protein factors of BRCA1 function,
they can test it in combination with other
genes to see if they can sensitize cancer
cells to available cancer drugs and determine
the efficacy of those drugs—a process
that would help physicians optimize their
prescriptions for their treatments. On the
other hand, they can also use their knowledge
of how the genes bind and function
to develop new compounds that can regulate
DNA repair processes and eventually
be used in preventative cancer drugs. In
the future, the scientists would like to fully
understand the pathways of BRCA genes to
the point where, by studying an individual’s
genes, they can advise the patient about
how likely it is that they will have cancer
and when they might be most susceptible
to cancer so that they may plan their futures
accordingly.
The fight against cancer is well and alive,
as researchers around the world make
strides towards treatments and preventions.
As the Sung Lab passionately scrapes
away the mysteries of BRCA1, we can be
hopeful that we are well on our way towards
answers for curing cancer.
ABOUT THE AUTHOR
LESLIE SIM
LESLIE SIM is a first year in Jonathan Edwards College at Yale University
interested in cancer research and biophysics. She enjoys fencing, food
photography, and exploring New Haven streets aside from being a writer for
the Yale Scientific.
THE AUTHOR WOULD LIKE TO THANK the Sung Lab at Yale and would
like to thank, in particular, Professor Patrick Sung, Dr. Weixing Zhao, and
Dr. Youngho Kwon for sharing their knowledge with me in interviews and
expressing enthusiasm about cancer research.
FURTHER READING
Zhao, Weixing et al. “BRCA1-BARD1 promotes RAD51-mediated homologous
DNA pairing.” Nature, vol. 550, no. 360, 4 October 2017, pp. 360-365.
www.yalescientific.org
December 2017
Yale Scientific Magazine
17