CONTACT: JENNIFER BROWN
Iowa City IA 52242
(319) 335-9917; fax(319) 384-4638
Release: Oct. 16, 2001
UI researchers receive grants to investigate immune system
IOWA CITY, Iowa -- University of Iowa microbiology researchers will use
a five-year, $1,169,162 grant from the National Institute of Allergy and Infectious
Diseases (NIAID) and a three-year, $260,000 grant from the American Heart
Association (AHA) to advance their studies on an important component of the
immune system. In addition to better understanding how the human immune system
normally functions, their research has implications for organ transplantation,
atherosclerosis and the treatment of a particular cancer associated with severely
weakened immune systems.
Gail Bishop, Ph.D., UI College of Medicine Distinguished Professor of microbiology
and internal medicine, and principal investigator on the NIAID grant, and
her colleagues are investigating the actions of a protein called CD40, found
in B-cell membranes. B cells are the white blood cells that make antibodies,
which fight infection.
"CD40 is very important in the activation of B-lymphocytes," Bishop
said. "CD40 delivers all kinds of signals to the cell. It tells the B
cell to divide, to make antibodies, and to die off when the infection has
been beaten and the need for the immune response is gone."
The CD40 protein consists of a portion outside the cell, which receives
molecular messages, and a tail inside the cell that initiates the transmission
of the signal to its final destination through a cascade of protein-protein
interactions. Studies from Bishop's and other's labs found that a family of
proteins, called TRAFs, interact with the CD40 tail and play an important
role in the signaling cascade.
To investigate how TRAF proteins function, Bishop and her team have developed
techniques to control how much and which type of TRAF, both normal and mutant,
the B cell makes. The researchers can also control when the cell will start
making the protein. This system allowed scientists to examine TRAF action
at protein levels that mimicked the normal amounts of protein found in a B
cell. Bruce Hostager, Ph.D., staff scientist in Bishop's lab and principal
investigator on the AHA grant worked out many of these techniques, which have
proved so important in studying CD40.
To investigate what happens when TRAF proteins and CD40 interact, the researchers
first had to determine where in the cell the two proteins got together. Within
a resting B cell the two proteins are in very different locations. However,
within a few minutes of stimulation, both proteins end up in the same place,
although the location was initially a mystery.
When the researchers used standard experiments to locate the proteins, they
didn't find anything. Back-tracking, the researchers finally found the missing
proteins in the insoluble parts of the cell membrane, in regions known as
These are patches of cell membrane that are rich in cholesterol and other
fatty molecules. Because of their composition, the rafts attract important
molecules that are key players in signaling pathways. These molecules like
to reside in the fat-friendly environment of the raft domains.
"There are a lot of signaling components that 'hang out' in these patches.
So the receptor and its friends that want to get together with signaling components
in a cell, might want to move to these domains," Bishop explained.
Now that it is known where the TRAF proteins and CD40 get together, the
UI team is investigating what happens to these molecules within the raft domain.
The UI researchers noticed that the amount of TRAF seemed to decline as
the signaling process went on, suggesting that it is being degraded. The UI
team is investigating how this process happens. The importance of the degradation
became clear as Bishop and her team pursued a new line of research, which
has implications for a cancer that is particular to B cells.
Epstein-Barr virus (EBV) is a herpes virus that infects B cells. This virus
causes mononucleosis in young adults, and most people are infected with EBV
by the time they are adults. In general, the latent infection is harmless
and does not produce any symptoms. However, for individuals with a highly
compromised immune system, such as people on immuno-suppressant drugs after
an organ transplant or individuals in the later stages of HIV infection, EBV
can reactivate and it can turn a B cell into a B cell lymphoma. EBV associated
lymphoma is now a major clinical complication of transplant biology.
Epstein-Barr virus makes a protein called LMP1 (latent membrane protein
1) that is absolutely required to transform a B cell into a B cell lymphoma.
It was recently discovered that LMP1 interacts with a TRAF protein. This similarity
of a cancer-causing protein with the CD40 protein excited Bishop and she and
the colleagues started to investigate the EBV protein.
The UI researchers found that the EBV protein mimics CD40 strikingly in
the B cell. It does all the things that CD40 does: it preserves viability,
and it activates the cell to divide and make antibodies. However, the EBV
protein causes much more powerful signals in B cells than does CD40.
"We found that in all the things that these two proteins can do to
a B cell, the LMP1 protein does it faster, longer and stronger," said
Bishop who also serves as director of the Cellular Activation in Cancer Program
of the Holden Comprehensive Cancer Center at the UI.
Knowing that TRAFs are normally gradually degraded over the course of CD40
signaling events, the researchers noticed that when the EBV protein was controlling
the signal, the amount of TRAF did not decline during the signaling process.
Activation turns the cell on, and the TRAFs subsequent removal seems to act
like a dimmer switch, slowly turning off the signal. However, the EBV protein
turns the cell on, but somehow the dimmer mechanism does not work and the
signal stays on.
In parallel with their on-going studies on CD40, Bishop and her team in
collaboration with George J. Weiner, M.D., director of the Holden Comprehensive
Cancer Center and C.E. Block Professor of Cancer Research and Internal Medicine
at the UI, have started to investigate LMP1 signaling in human B lymphomas.
"It's exciting to bring the knowledge we gain about a normal cellular
protein, CD40, to bear on what goes wrong in a signaling pathway in cancer,"
In addition to Bishop and Hostager, other UI researchers involved in these
studies include Lisa Busch, Ph.D., Kevin Brown, Ph.D., and Mekhine Baccam,
Ph.D., all of whom recently earned their doctoral degrees in Bishop's lab;
Sokol Haxhinasto and Carissa Moore, graduate students; Ping Xie, Ph.D., and
So-youn Woo, Ph.D., postdoctoral fellows; Laura Stunz, Ph.D., staff scientist,
and Luis Ramirez, research technician.
University of Iowa Health Care describes the partnership between
the UI College of Medicine and the UI Hospitals and Clinics and the patient
care, medical education and research programs and services they provide. Visit
UI Health Care online at www.uihealthcare.com.