| May 14, 2002
Prolactin Proactive in Promoting
PA) - In the pursuit of novel cancer therapies, researchers
at the University of Pennsylvania School of Medicine
describe new mechanisms by which the hormone prolactin
induces the growth and spread of breast cancer, a disease
that affects one in nine women.
As a hormone, prolactin is necessary for the production
of breast milk. However, its role in stimulating the
growth of breast cancer has been only recently recognized
in humans, as recent studies have found that prolactin
is made by human breast cancer and that elevations in
prolactin levels in the blood significantly increase
the risk of developing this disease.
In the report, appearing this month in the Proceedings
of the National Academy of Sciences, researchers describe
that the alteration of the structure of one protein
that binds prolactin results in a dramatic inhibition
of the growth of breast cancer in the lab. This finding
challenges the current dogma of how protein hormones
like prolactin function and also provides researchers
with new strategies in their therapeutic attack on breast
"Traditionally, it was thought that protein hormones,
like prolactin, only work on the outside of cells -
as if their only job was just to hit the 'on' switch,"
said Charles V. Clevenger, MD, PhD, associate
professor in the Penn Department of Pathology and Laboratory
"Contrary to established theory, our research has
shown that prolactin combines with another protein called
cyclophilin B to physically enter the cell and directly
activate the process that turns on genes and trigger
the growth of breast cancer cells."
"Here we show that prolactin clearly works inside
the cell to turn on genes", said Michael Rycyzyn,
a postdoctoral fellow in the Clevenger lab and co-author
of this study, "and by using modified forms of
cyclophilin B we can stop this process and block the
growth of breast cancer." In doing this, their
lab has uncovered a new pathway through which hormones
work, and in turn, discovered a target-rich environment
for cancer researchers to explore.
The research presented in this study was provided by
grants from the National Institutes of Health and the
American Cancer Society.
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You can find the original article online at www.pnas.org