John Cambier, Ph.D.
Chairman of Integrated Department of Immunology
Integrated Department of Immunology
Room 1004 Goodman Building
National Jewish Center for Immunology
and Respiratory Medicine
1400 Jackson Street
Denver, Colorado 80206
John.Cambier@njh.org
EDUCATION/EXPERIENCE
HONORS, AWARDS & PATENTS
PROFESSIONAL ACTIVITIES
LAB PERSONNEL
Research Interests
Development, growth and differentiation
of cells is regulated by environmental queues which take the form of soluble or
cell associated ligands that bind cell surface or intracellular receptors. In
some cases, such as in the immune system, receptor mediated regulation of cell
biology is very complex, involving many incoming signals that must be properly
integrated. Signal integration can be accomplished at a number of molecular levels.
For example, distinct receptor types may be coupled via distinct transduction
pathways to unique sets of transcription regulators that complement each other.
Alternatively, signals can be integrated earlier at the level of molecular events
in transduction pathways, with signaling cascades activated by one receptor being
modified by those activated by another. We have been interested in transduction
and integration of regulatory signals in lymphoid cells in part because aberrancies
in these mechanisms may lead to autoimmunity and immunodeficiency. Ongoing efforts
in the laboratory address 5 major questions.
The first is the molecular mechanism underlying HIV gp120 inactivation of T
cells. Binding of the gp120 virus coat protein to one of its receptors, CD4, renders
T cells hypo responsive to antigen receptor stimulation and prone to undergo death
by apoptosis. Our studies indicate that this inhibitory signaling is mediated
by the CD4 associate tyrosine kinase Lck, via secondary associations with the
SH2-containing inositol 5-phophatase SHIP and the linker downstream of Kinase
Dok. Dok acts as a linker to rasGAP, a regulator of p21ras. CD4 aggregation by
gp120 leads to phosphorylation of these effectors and blockade of Akt and ras
activation following TCR stimulation. Despite T cell expression of partially redundant
SHIP2 and Dok2, TCCR function is partially restored in SHIP and Dok knockout mice.
These findings indicate that SHIP and Dok play important roles in gp120 induced
loss of T cell function in AIDs. Further studies address the basis of Lck/SHIP/Dok/rasGAP
interaction and downstream function.
In a second series of experiments we are trying to determine the molecular
basis of anergy, a particular type of immunologic tolerance. We have discovered
that anergy in B cells can be mediated by destabilization of the multi-subunit
antigen receptor complex. As a consequence, information is not transduced from
the antigen binding substructure (mIg) to the transmembrane transducer substructure
(Ig-a/b) of the receptor. This prevents transmembrane transduction of the signal.
Ongoing studies seek to determine the physiologic significance of this mechanism,
and to determine if it is generalizable to T cell antigen receptors. Finally,
based on these findings we are exploring approaches for pharmacologic induction
of receptor destabilization. For example, we hypothesize that antibodies against
epitopes in the Ig-a/b-mIg interface may block signal transduction. Such agents
might be useful for immunosuppression and for therapy in autoimmunity.
The third area of interest is the molecular basis of integration of signals
transduced concurrently by B cell antigen receptors (BCR), the type 2 complement
receptors (CR2) and receptors for immunoglobulin G constant regions (FcgRIIB 1).
BCR and CR2 exhibit positive cooperativity wherein receptor co-crosslinking causes
as much as 10,000 for increase in BCR signal output. BCR and FcgRIIB exhibit negative
cooperativity wherein co-crosslinking of FcgRIIB terminates BCR signaling. Our
studies address the molecular basis of cooperativity of the operative signaling
pathways. Findings demonstrate that both positively and negatively cooperative
mechanisms target levels of phosphatidylinositol 3,4,5 triphosphate (PIP3) - a
critical signaling intermediary. They do this by affecting synthesis of PIP3 by
PI3-kinase and degradation of PIP3 by the inositol phosphatase SHIP. Among other
aspects of these studies we are undertaking crystallographic studies on complexes
of SHIP, the adaptor Grb2 and the FcgRIIB receptor tail. Such complexes form in
vivo during inhibitory signaling. Finally, the adaptor molecule Downstream of
kinase, Dok, is also involved in inhibitory FcR signaling. It is recruited by
SHIP and, in turn, recruits rasGAP, an activator of the GTPase activity of p21ras.
The physical basis of interaction of these molecules, as well as their functions
is a major focus of our studies. Finally, we have recently extended these studies
to FceRI-FcgRIIB interactions on mast cell.
The fourth area of focus in the laboratory is signal transduction that occurs
in B cells during cognate interactions with helper T cells. Of particular interest
is signal transduction by MHC class II molecules. Recent studies in the laboratory
have revealed that antigen stimulation of resting B cells leads within a few hours
to association of MHC class II molecules with the transducers Ig- a and Ig-b.
These molecules were previously thought to associate only with the B cell antigen
receptors. Ligation of MHC class II molecules on "primed" B cells by
TCR/CD4 during cognate interactions appear to lead to signal transduction via
the associated Ig-a/Ig-b dimers. Future studies will define the molecular basis
and biological consequences of MHC mediated signaling.
Our fifth area of research focus is the decline in B cell function seen during
aging. In many individuals, antibody responses to infectious agents are of decreasing
affinity and effectiveness due in part to cessation of B cell production and resultant
dominance of the peripheral repertoire with antigen experienced and thus long-lived
marginal zone-like cells. Our studies address the dynamics of this process and
the molecular basis of B lymphopause. The latter appears to result from decreased
responsiveness of progenitor cells to interleukin 7. Current studies explore the
possibility that this unresponsiveness results from impaired expression and/or
signal transduction by IL-7 receptors.
Selected Publications
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Tamir, I., Stolpa, J.C., Helgason, C.D., Nakamura, K., Bruhns, P., Daeron,
M., and Cambier, J.C. 2000. The RasGAP-binding
protein p62dok is a mediator of inhibitory FcgRIIB signals in B cells. Immunity.
12:347-358. [Abstract]
-
Benschop, R.J., K. Aviszus, X. Zhang, T. Manser, J.C.
Cambier, and L.J. Wysocki. 2001. Activation and anergy in bone marrow B
cells of a novel immunoglobulin transgenic mouse that is both hapten-specific
and autoreactive. Immunity. 14:33-43. [Abstract]
-
Lang, P., Stolpa, J.C., Freiberg, B.A., Crawford, F., Kappler, J., Kupfer,
A., Cambier, J.C. 2001. TCR-induced transmembrane
signaling by peptide/MHC class II via associated Ig-a/b dimers. Science. 291:1537-1540.
[Abstract]
-
Brauweiler, A., Tamir, I., Marschner, S., Helgason, C.D., and Cambier,
J.C. 2001. Partially distinct molecular mechanisms mediate inhibitory FcgRIIB
signaling in resting and activated B cells. 167:204-211. [Abstract]
-
Ott, V., Fong, D.C., and Cambier, J.C. 2001.
Fcg-RIIB as a potential molecular target for intravenous gamma globulin therapy.
Journal of Allergy and Clinical Immunology. 108:S95-S98 [Abstract]
- Benschop, R.J., Brandl, E., Chan, A.C. and Cambier,
J.C. 2001. Unique signaling properties of B cell antigen receptor in mature
and immature B cells: implications for tolerance and activations. The Journal
of Immunology. 167:4172-4179. [Abstract]
Bibliography
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