Research Interest
- Molecular Genetics of Lymphocyte Development and Leukemogenesis
My lab is working on the molecular genetics of lymphocyte development. Our goal is to understand how differential expression of signal transduction proteins can determine the differential biological responses of developing lymphocytes to signals provided by antigen receptors, co-receptors, adhesion molecules and cytokines. We are also exploring the mechanisms by which developing lymphocytes with perturbed signal processing can be shunted from normal developmental pathways to leukemogenesis.r
The signal transducers that we are currently working on are all guanine nucleotide exchange factors (GEFs), which convert GTPases from inactive GDP-bound forms to active GTP-bound forms. Four of the GEFs under investigation are members of the recently discovered RasGRP family. These Ras/Rap-specific GEFs are differentially expressed during T and B cell development. They are activated by translocation to membranes in response to lipid second messengers generated via receptor signalling. We are using fluorescence microscopy and expression of domain-specific mutants in cell lines to identify the mechanisms by which RasGRPs are activated. Cell lines are also used to identify which signal transduction pathways are quantitatively altered by variations in RasGRP expression, and to determine how these shifts in siganlling alter the biological responses of cells to specific receptor ligands.
We are making genetically modified mice to determine how individual RasGRP family members and other GEFs influence developmental progression, lineage commitment, immunological selection and propensity to leukemogenesis. We have found that RasGRP1 is able to drive pre-T cell receptor-independent differentiative progression of thymocytes, as well as enhancing the survival of thymocytes with weak T cell receptor signalling. The thymocytes which evade beta-selection and negative selection due to their excessive expression of RasGRP1 are highly prone to progress towards leukemogenesis. In contrast, the CDC42/Rho-specific GEF Dbs confers expansion of immature thymocytes but these cells remain dependent on pre-TCR for differentiative progression and become hyper-sensitive to negative selection once the complete T cell receptor is assembled. RasGRP1 and Dbs over-expression also cause stage-specific perturbations of B cell development, which may be due to shifts in the sensitivity of pre-B cells to apoptosis versus proliferative signals provided by the pre-B cell receptor.
Publications
Selected Publications
2007
Beaulieu N, Zahedi B, Goulding RE, Tazmini G, Anthony KV, Omeis SL, de
Jong DR, & Kay RJ. Regulation of RasGRP1 by B cell antigen receptor
requires cooperativity between three domains controlling translocation
to the plasma membrane. Mol Biol Cell 18 (8): 3156-68, 2007.
View Abstract
Johnson JE, Goulding RE, Ding Z, Partovi A, Anthony KV, Beaulieu N,
Tazmini G, Cornell RB, & Kay RJ. Differential membrane binding and diacylglycerol recognition by C1 domains of RasGRPs. Biochem J 406 (2):
223-36, 2007.
View Abstract
2005
Klinger
MB, Guilbault B, Goulding RE, & Kay RJ.
Deregulated expression of RasGRP1 initiates thymic lymphomagenesis
independently of T-cell receptors. Oncogene 24 (16): 2695-704, 2005.View
Abstract
2004
Klinger
MB, Guilbault B, & Kay RJ. The RhoA- and
CDC42-specific exchange factor Dbs promotes expansion of immature
thymocytes and deletion of double-positive and single-positive
thymocytes. Eur J Immunol
34 (3): 806-16, 2004.
View Abstract
Guilbault B, & Kay RJ. RasGRP1 sensitizes an immature B cell line to
antigen receptor-induced apoptosis. J Biol Chem 279 (19): 19523-30,
2004.
View Abstract
2003
Norment AM, Bogatzki LY, Klinger M, Ojala EW, Bevan MJ, & Kay RJ.
Transgenic expression of RasGRP1 induces the maturation of
double-negative thymocytes and enhances the production of CD8
single-positive thymocytes.
J Immunol 170 (3): 1141-9, 2003.
View Abstract
Open Positions
None Available at this time.