• Cell adhesion and migration
• Protein-protein interactions
• Protein phosphorylation and kinase signalling
• Integrins
• cAMP dependent protein kinase (PKA)

My research is aimed at understanding the molecular mechanisms governing cell adhesion and motility, in particular those involving white blood cell function in normal as well as in pathologic outcomes.

Circulating white blood cells represent the immune system’s frontline defence against infection. The successful and accurate targeting of white blood cells to inflamed tissues is facilitated by cell adhesion receptor proteins expressed on the surface of these cells. However, aberrant function of these receptor proteins and the cellular signals that regulate them can lead to diseases of the immune system, including leukemia, lymphoma and autoimmunity.

My research is focussed on understanding the differences in cellular signalling between healthy and diseased cells in order to explore and evaluate novel signalling targets for therapeutic intervention in blood diseases. My laboratory employs a multi-disciplinary approach that encompasses cell biology, protein biochemistry, molecular biology and immunology.

α4 integrins are cell surface receptor proteins that regulate aspects of leukocyte function, including adhesion and migration across vascular and lymphoid tissues. They play important roles in the development of a variety of blood diseases.

Interaction between α4 with its counter-receptor expressed by vascular endothelial cells is an important element for leukocyte recruitment to areas of wound and inflammation. However, excessive leukocyte recruitment to explicit tissues has undesirable consequences; for example, those that occur in chronic inflammatory diseases such as multiple sclerosis, Crohn’s disease and rheumatoid arthritis.

α4 integrins also impact graft versus host disease (GVHD), a complication of allogeneic bone marrow transplantation. This is exemplified in mouse model studies showing a reduced or delayed incidence of disease when α4 function is neutralized. In the ‘expansion phase’ of GVHD, this is attributable to blockade of alloreactive T-cell homing to target organs. During the ‘induction phase’, α4 acts as a costimulatory molecule in classical T-cell receptor ligation to achieve T-cell activation and subsequent expansion.

In lymphoid tumours, α4 integrins mediate lymphocyte targeting to specific peripheral tissues and regulate metastasis. Furthermore, interaction between α4 with its adhesion substrate has been shown to confer drug resistance to chemotherapeutic agents, thus reducing treatment efficacy. Thus, the elucidation of α4 integrin mediated signalling in leukocytes will impact our understanding of the pathology of autoimmune diseases, GVHD, and leukemia and lymphoma.
 
I had previously discovered that the cytoplasmic portion of α4 directly and specifically anchors TypeI PKA holoenzyme in a spatially compartmentalized manner (Nat Cell Biol 9:415, Mol Biol Cell 19:4930). This interaction facilitates PKA mediated phosphorylation of α4 that is restricted at the leading edge of polarized cells. Binding of the signalling adaptor protein, paxillin, to α4 is blocked when α4 is phosphorylated by PKA. Thus, the spatial restriction of phosphorylated α4 at the leading edge promotes lammelipodia formation, while paxillin association with non-phosphorylated α4 at the lateral cell edges prevents it. This combination acts to maintain cell polarity to achieve directional cell migration. Mistargeting of TypeI PKA inhibited α4-dependent T-cell migration, suggesting blockade of α4-TypeI PKA interaction may be an equally effective therapeutic strategy.

Ongoing studies will address the following:

• Elucidating the molecular details governing integrin-TypeI PKA interaction to support the design of novel therapeutics for inhibiting α4-dependent migration
• Identification of TypeI PKA phosphorylated substrates and mechanistic elucidation of their function in T-cell signalling and integrin-dependent migration
• Identification of the specific phosphatase/s for dephosphorylation of α4
• To understand the signalling relationship between integrins, PKA and T-cell receptor in T-cell stimulation and proliferation

Lee HS*, Lim CJ*, Puzon-McLaughlin W, Shattil SJ, Ginsberg MH. RIAM Activates Integrins by Linking Talin to Ras GTPase Membrane-targeting Sequences. Journal of Biological Chemistry (2009) 284:5119-5127.     PMID: 19098287   *equal contribution

Lim CJ*, Kain KH*, Tkachenko E, Goldfinger LE, Gutierrez E, Allen MD,  Groisman A, Zhang J, Ginsberg MH. Integrin-mediated protein kinase A activation at the leading edge of migrating cells. Molecular Biology of the Cell (2008) 19:4930-41. PMID: 18784251   *equal contribution

Lim CJ, Han J, Yousefi N, Ma Y, Amieux PS, McKnight GS, Taylor SS, Ginsberg MH. α4 Integrins are Type I cAMP-dependent protein kinase-anchoring proteins. Nature Cell Biology (2007) 9:415-421. PMID: 17369818

Han J, Lim CJ, Watanabe N, Soriani A, Ratnikov B, Calderwood DA, Puzon-McLaughlin W, Lafuente EM, Boussiotis VA, Shattil SJ, Ginsberg MH. Reconstructing and Deconstructing Agonist-induced Activation of Integrin  αIIbβ3 (Platelet GPIIb-IIIa). Current Biology (2006) 16:1796-1806.  PMID: 16979556

Lim CJ, Zawadzki KA, Khosla M, Secko DM, Spiegelman GB, Weeks G. Loss of the Dictyostelium RasC protein alters vegetative cell size, motility and endocytosis. Experimental Cell Research (2005) 306:47-55. PMID: 15878331

Kae H, Lim CJ, Spiegelman GB, Weeks G. Chemoattractant-induced Ras activation during Dictyostelium aggregation. EMBO Reports (2004) 5:602-606. PMID: 15143344

Wessels D, Brincks R, Kuhl S, Stepanovic V, Daniels KJ, Weeks G, Lim CJ, Spiegelman G, Fuller D, Iranfar N, Loomis WF, Soll DR. RasC plays a role in the transduction of temporal gradient information in the cAMP wave of Dictyostelium. Eukaryotic Cell (2004) 3:646-662. PMID: 15189986

Lim CJ, Spiegelman GB, Weeks G. Cytoskeletal regulation by Dictyostelium Ras subfamily proteins. Journal of Muscle Research and Cell Motility (2002) 23:729-736.  PMID: 12952071

Lim CJ, Spiegelman GB, Weeks G. RasC is required for optimal activation of adenylyl cyclase and Akt/PKB during aggregation. The EMBO Journal (2001) 20:4490-4499. PMID: 11500376  *Cover art

Fellow, Career Development Program, The Leukemia and Lymphoma Society (U.S.A.), 2004 – 2007

Travel Award, North American Vascular Biology Organization (NAVBO), 2007

Outstanding Poster Award, Vascular Matrix Biology and Bioengineering Workshop (NAVBO), 2007

Canadian Institutes of Health Research (CIHR) Studentship, 1997-2002