ArticlePDF Available

Cellular Polka and Immune Cell Signalling


Abstract and Figures

Overview of our T cell signaling research, suitable for readers with and without a science background.
No caption available
Content may be subject to copyright.
Cellular Polka and
Immune Cell Signalling
Professor Brian C. Schaefer
A Century of Immunology
Impaired function of the immune system is
known to be responsible for a vast number
of medical conditions, such as cancers,
inflammatory disorders, allergies and
autoimmune diseases, where the immune
system attacks the body’s own tissues
instead of fighting infections. Since 1908,
when Russian biologist Ilya Ilyich Mechnikov
and German biologist Paul Ehrlich were
awarded a Nobel prize for their studies of
the immune system, research in the field of
immunology has advanced and developed to
an incredible degree. To this day, a significant
number of researchers and groups dedicate
their life’s work to new discoveries in immune
system biology, with the aim to help treat or
prevent human disease.
Immunology research has provided us
with many revolutionary discoveries, from
identifying the dierent cellular components
of the immune system to developing
vaccinations and therapeutic strategies to
combat many devastating diseases, including
smallpox, polio and measles. Despite these
incredible advancements made in our
understanding of immune system biology,
gaps in our knowledge of immune function
and a lack of therapies for many immune
system disorders continue to be major world-
wide contributors to deadly disease.
The Finer Details of Immunology
From the earliest accounts of immunology
in 1549, with the inoculation of smallpox,
our understanding of the immune system
has advanced significantly. During the 20th
century, researchers identified the various
components of the immune system and
started to unravel the key mechanisms that
allow us to defend ourselves from harmful
invading organisms.
White blood cells are key players in immune
system defence and can be divided into B
cells and T cells that engage in two dierent
kinds of immune response. B cells produce
antibodies. These are large proteins that
circulate in the blood and fight against
foreign bacteria and viruses, by binding
to specific proteins found on their surface
(antigens). Because of the vast diversity of B
cells, antibodies can be generated to bind
nearly any antigen.
This ability to determine friend from foe
and recognise what is part of yourself and
what has come from elsewhere is key to
targeting harmful invading bacteria and
viruses for destruction. The binding of
antibodies blocks or impairs the ability of the
pathogen to function and can target these
invaders for destruction by other cells in the
immune system.
Another of the vital components of our
immune system are the T cells. T cells
recognise foreign antigens on the surface
of host cells that have been invaded and
destroy the infected cells. T cells have
antigen receptors on their cell surface
responsible for recognising and binding
fragments of antigens – proteins the body
recognises as foreign. This antigen receptor,
called the T cell receptor, activates T cells
through a biochemical signal that provokes
them to attack.
Professor Brian Schaefer began his career
in this field as a postdoc, working with Drs
Philippa Marrack and John Kappler, where
Immunology remains an important branch of medical and biological
sciences, providing us with protection against infection and disease.
Professor Brian Schaefer of the Uniformed Services University, Bethesda,
has dedicated his research to elucidating the molecular mechanisms of
immune cell signalling, with the hope of discovering potential therapeutic
targets for immunological drugs – to ultimately treat human diseases
including autoimmunity, gra rejection and cancers.
he started to investigate the mechanisms
of immune cell signalling through the T cell
receptor. He has since deepened his research
within this area, and he has expanded his
research to additional areas, including host
defences, cellular mechanisms of disease, and
cell injury and repair.
Professor Schaefer continued his work in this
field when he joined the Uniformed Services
University, where he dedicated his attention
to defining the molecular mechanisms of T
cell receptor signalling to a transcription factor
called Nuclear Factor kappa-B (NF-ĸB) – a
protein that controls gene expression. NF-ĸB is
of central importance in T cell biology because
Super-resolution microscopy reveals the
components of the POLKADOTS signalosome,
showing that Bcl10 (blue), Malt1 (green) and the
activated IKK complex (pink) are all components
of POLKADOTS filaments.
it turns ‘on’ the expression of many genes
involved in the changes that occur to T
cells when they are activated during an
immune response.
When a T cell receptor recognises and binds
to an antigen fragment, it initiates a series of
signals that ultimately activate NF-ĸB leading
to T cell activation and an appropriate
immune response. Professor Schaefer’s team
has revealed the nature of NF-ĸB activation
through the T cell receptor, discovering that
activating NF-ĸB occurs in a digital, switch-
like manner.
T Cell Receptor Signalling
The signalling cascade involved in T cell
activation through the T cell receptor is
extremely complex, with many dierent
components influencing the process.
Professor Schaefer’s team has investigated
the many components of the signalling
cascade that ultimately drive NF-ĸB
activation and the consequent activation of T
cells and their rapid multiplication aer they
detect a foreign protein that is important for
an appropriate immune response.
NF-ĸB is of particular importance, as it
stimulates the generation of a large number
of other molecules that play a role in the
response. The adaptor protein, Bcl10, also
plays a large role in transmitting signals from
the T cell receptor to NF-ĸB. Without the
Bcl10 protein, T cells are unable to multiply
and develop aer T cell receptors engage
with foreign antigens.
At the same time that T cells activate
NF-ĸB, Bcl10 is degraded and removed.
This suggests that this degradation of
Bcl10 may be a regulatory mechanism that
limits T cell receptor signalling to NF-ĸB,
acting as a brake on the immune response.
Although previously, the existence of such
a mechanism was controversial, more
recent studies by Professor Schaefer’s
group and others have confirmed that
T cell receptor stimulation induces this
intracellular degradation, precisely targeting
and delivering components of the cell such
as Bcl10 for ultimate destruction. This
work revealed that the process of Bcl10
degradation regulates functions that control
T cell survival and multiplication during an
immune response.
Professor Schaefer and his colleagues
explored further the link between T cell
receptor-induced destruction of Bcl10 within
the cell and the modulation of activated T
cell responses. The team revealed that as T
cells target the Bcl10 protein for destruction,
this process also reduces the ability of T
cell receptors to activate NF-ĸB, and limits
the NF-ĸB induced immune response. They
suggest that this mechanism modulates
antigen receptor signalling and propose that
this process may protect T cells from the
adverse consequences of unrestrained NF-ĸB
activation and an overactive immune system,
such as cellular aging.
Building the Structures for Signalling
Professor Schaefer states that, ‘our overall
goal is to define how the transmission
of cellular signals is regulated by the
formation of organised structures, called
“signalosomes”, within the cell.’ Early T
cell receptor signals involve the formation
of a CBM (Carma1-Bcl10-Malt1) complex,
containing the Bcl10 adaptor protein,
Carma1 (a larger adaptor protein) and
Malt1 (an enzyme that breaks down
proteins). Assembly of this complex triggers
activation of another signalling complex, IKK,
the key regulator of NF-ĸB activation. Aer
being activated by IKK, NF-ĸB is able
to move into the nucleus of the cell to
activate target genes.
Professor Schaefer and his colleagues noted
that there was a lack of understanding of
how these proteins interact, and conducted
research to elucidate the signalling
mechanisms involved in this process. In their
early work, Professor Schaefer’s group had
identified T cell receptor-induced formation
of signalling clusters of Bcl10 and Malt1,
which make up a ‘signalosome,’ which they
named POLKADOTS, an acronym describing
the dotted appearance of these structures
within a stimulated T cell.
The team found that the abundance of these
signalling clusters is highly correlated with
how much NF-ĸB moves into the nucleus,
suggesting that the POLKADOTS structure
plays a role in activating NF-ĸB. Professor
Schaefer remarks that, ‘now that we know
something about what this signalling
machine does, we are trying to understand
exactly how it works.This information could
ultimately lead to new drugs for altering
immune responses to treat disease.’
‘Our overall goal is to define how the transmission of cellular
signals is regulated by the formation of organised structures,
called “signalosomes”, within the cell.
T cell receptor stimulation causes POLKADOTS formation and NF-ĸB activation. Confocal microscopy shows that delivery of an activating signal
to the T cell receptor causes Bcl10 and Malt1 to move into filamentous POLKADOTS, NF-ĸB then moves from the cytoplasm into the nucleus –
identified by staining nuclear DNA.
The Bcl10 protein’s ability to form filaments is correlated with its ability
to activate NF-ĸB. Professor Schaefer’s research group found that the
active form of IKK is located only at the POLKADOTS signalosome,
providing compelling evidence that this filamentous structure controls
NF-ĸB activation.
Furthermore, when these filaments cluster around pre-existing
aggregates of a protein called p62, POLKADOT structures form.
They confirmed this finding by disrupting p62, which stopped
POLKADOTS from forming and blocked NF-ĸB from being activated.
The team showed that in mice genetically modified to remove p62
there was a change in T cell receptor-dependent IKK and NF-ĸB
activation and T cell activation during an immune response.
Together, their work has shown that p62, Bcl10, and Malt1 form
POLKADOTS – the ‘signalosome’ that directs the activation of NF-ĸB,
ultimately controlling the rate at which target genes are turned ‘on’ or
activated. This makes POLKADOTS an attractive target for developing
immunomodulatory drugs. For example, drugs inhibiting formation of
POLKADOTS may have applications in the treatment of autoimmune
diseases or other conditions that are characterised by an undesired
overactivation of T cells.
Looking to the Future
In order for Professor Schaefer’s group to reach their goal of identifying
specific targets for pharmacological drugs to modify immune
responses, it is important to define the signalling mechanisms in
molecular detail. Professor Schaefer’s team is engaged in studies
to elucidate the molecular mechanisms by which the POLKADOTS
‘signalosome’ precisely controls the activation of NF-ĸB.
Professor Schaefer reveals that, ‘our approach employs several
dierent technical methods, including biochemistry, molecular
biology, microscopy, and, most recently, mathematical analyses
and modelling with our collaborator, Professor Wolfgang Losert,’ who
is working with the team to develop algorithms for analysing patterns
of protein distribution.
To better understand how T cells turn o the POLKADOTS
‘signalosome,’ collaborations have also been established with
Professors You-Wen He at Duke University School of Medicine and
Thomas Conrads at Inova Schar Cancer Institute. Indeed, the majority
of Professor Schaefer’s work is now highly collaborative, as he has
found that joining forces with other investigators with complementary
expertise, ‘greatly increases the breadth of scientific and technical
approaches, facilitating a much deeper mechanistic understanding of
our scientific questions than could be achieved by my group working
in isolation.’
Professor Schaefer explains that, ‘we are completing a study
demonstrating that the composition of the POLKADOTS signalosome
changes substantially over time, and that it is actually transported and
consolidated at a specific location within the cell. These movements
are connected to a change in function of the signalosome.’ Discovering
the molecular mechanisms by which the POLKADOTS ‘signalosome’
regulates T cell receptor activation of NF-ĸB will bring the team closer
to their goal or identifying targets for novel immunomodulatory drugs.
‘We are also in the midst of an exciting collaboration with the Advanced
Imaging Center at the Howard Hughes Medical Institute’s Janelia
Farm facility,’ Professor Schaefer reports. ‘In this work, we are using
unique cutting-edge microscopes to make high-resolution videos of
the POLKADOTS signalosome in living T cells. The resulting movies will
document the changes in this “signalosome” over time, enabling us to
better understand how this complex molecular machine performs its
functions within the cell.’ The hope is this information can be used to
develop new treatments for a wide array of human diseases, such as
cancer, autoimmunity and gra rejection.
‘We are using unique cutting-
edge microscopes to make high-
resolution videos of the POLKADOTS
signalosome in living T cells. The
resulting movies will document
the changes in this signalosome
over time, enabling us to better
understand how this complex
molecular machine performs its
functions within the cell.
Steps in signalling from the T cell receptor to NF-ĸB. When a T cell
receptor binds its target, a signal is sent, causing assembly of the CBM
complex just inside the cell membrane. Next, Bcl10 interacts with p62,
forming the filament-shaped POLKADOTS signalosome that contains
Malt1 and IKK. This causes IKK to become activated (P-IKK). P-IKK then
transmits a signal causing NF-ĸB to move from the cell cytoplasm into
the nucleus, where it turns on many genes required for T cell function.
At the same time this activation signal is being turned on by the T cell
receptor, it is also being partly turned o by autophagy of the POLKADOTS
filaments, a destruction process directed by p62 that destroys the Bcl10
protein, reducing activation of NF-ĸB.
Meet the researcher
Brian C. Schaefer is a Professor in the Department of Microbiology and
Immunology at the Uniformed Services University (USU) in Bethesda,
MD. Professor Schaefer achieved a Bachelor of Science Degree in
Biology from the Massachusetts Institute of Technology in Cambridge
and continued to work towards his passion at Harvard University
where he was awarded his PhD in Immunology in 1995. From 1996
until 2002, Professor Schaefer worked with Drs Philippa Marrack and
John Kappler, investigating Immunology and cell signalling. In 2002,
he was oered a faculty position at USU, where he continues to focus
his research on exploring signal transduction mechanisms of immune
cells including host defences, cell mechanisms of disease and cell
injury and repair. Professor Schaefer is a Chair of the Faculty Advisory
Committee of the USU Biomedical Instrumentation Centre and sits
on the Editorial Board of Frontiers in Cell and Developmental Biology.
Professor Schaefer has achieved numerous honours and awards
for his outstanding contributions to Microbiology and Immunology
research including a Kimmel Scholar Award in 2004, a competitive
research award from the Dana Foundation Program in Brain and
Immuno-imaging in 2005 and the USU Henry Wu Award for excellence
in basic science research in 2016.
T: (+1) 301 295 3402
Professor Wolfgang Losert, University of Maryland
Professor Arpita Upadhyaya, University of Maryland
Professor You-Wen He, Duke University School of Medicine
Professor Thomas Conrads, Inova Schar Cancer Institute
Professor Christopher Broder, Uniformed Services University
Professor Andrew Snow, Uniformed Services University
Professor Igor Brodsky, University of Pennsylvania
Professor Hao Wu, Harvard University
National Institutes of Health (NIH)
LM Kingeter, S Paul, SK Maynard, NG Cartwright, and BC Schaefer,
Cutting Edge: T cell receptor ligation triggers digital activation of NF-ĸB,
The Journal of Immunology, 2010, 185, 4520–4.
S Paul, AK Kashyap, W Jia, Y-W He and BC Schaefer, Selective
Autophagy of the Adaptor Protein Bcl10 Modulates T Cell Receptor
Activation of NF-ĸB, Immunity, 2012, 36, 947–958.
S Paul and BC Schaefer, A new look at antigen receptor signaling to NF-
ĸB, Trends in Immunology, 2013, 34, 269–81.
S Paul, MK Traver, AK Kashyap, MA Washington, JR Latoche and
BC Schaefer, T Cell Receptor Signals to NF-ĸB Are Transmitted by a
Cytosolic p62-Bcl10-Malt1-IKK Signalosome, Science Signaling, 2014,
7, ra45.
Professor Brian C. Schaefer
Department of Microbiology and Immunology
Uniformed Services University of the Health Sciences
Bethesda, MD
ResearchGate has not been able to resolve any citations for this publication.
ResearchGate has not been able to resolve any references for this publication.