In the World of Integrin and Cytoskeleton

 

         Jianxun Li, Ph.D., Associate Professor

 

 

           

 

 

     

     

      Department of Oral Biology

      College of Dentistry

      University of Illinois at Chicago

      Tel: 312-996-3520

      Email: jxli@uic.edu

 

 

 

 

 

 

 

 

The General Direction of Our Research

 

The research focus of our laboratory is cell adhesion, a essential physiological event observed in every aspect of our lifes including immune cell activation, cell proliferation and differentiation, and tumor angiogenesis. We believed that cytoskeleton, membrane and membrane-bound receptors constitute a unified entity, such that a change in one element of the unit signals to other components of the units. However, solid evidence is needed to support this theory. Our research stresses the importance of cytoskeleton which not only functions as a structural support in these events, but also as part of the signaling and regulatory apparatus.

 

Understanding the activation mechanism of b2 integrin

b2 integrin is the key adhesion molecule in the activation of leukocytes. The activation of b2 integrin, i.e. its binding to various ligands, is essential for the activation of leukocytes in immune defenses. While lacking b2 integrin-mediated adhesion causes immune deficiency, excessive integrin-mediated cell adhesion associates with autoimmunity. In the case of b2 integrin, its ligand-binding activity on the extracellular surface of the plasma membrane is tightly regulated by a number of intracellular signals originating from other membrane receptors such as T cell receptors or chemokine receptors. The question is how this signal transduction works?

Our laboratory and others have demonstrated that the b2 integrin molecules are maintained in an inactive form in resting leukocytes; the molecules are immobilized on the cell membrane in a diffused distribution by constraints from cytoskeletal complex. Activation signals cause the cytoskeletal complex to relax. Relaxation of the cytoskeletal constraint puts integrin in a free diffusion mode and facilitates the formation of clusters and conformational change that provide high avidity and affinity binding to the ligands. Thus, the cytoskeletal components controlling the inactive b2 integrin molecules are termed by our laboratory as “preactivation cytoskeletal complex”. Several proteins have been located into this complex including PKC, MacMARCKS, Dynamitin, Calmodulin, and talin.

In cardiovascular diseases:

Our research funded by American Heart Association is to investigate the b2 integrin activation during the minor inflammation in circulation. Activation of this adhesion molecule many contribute to the accumulation of “foam cells” and atherosclerosis. We are focusing on determining the activation status of b2 integrin in leukocytes and if they are activated, how to calm it down.

 In bacterial infection:

In many cases of infections, the final killer is the overwhelm septic responses that proven to be fatal. Uncontrolled activation of leukocytes plays essential role in this case. Because b2 integrin is a key regulator of leukocytes, our laboratory is currently testing the inhibitors of integrin molecules in treating septic shocks.

In Cancer research:

One of main difficulties in fighting cancer is metastasis. Again, integrin plays very important roles in this process. In order for cancer cells to break away from the original sites, it is necessary to down regulate integrin adhesion. For these cancer cells to firmly adhere in a new location, however, the integrin molecules are then upregulated. Thus is a very fine tuned system. We are currently investigating how cytoskeleton is involved in the process.

 

Our specialized skills in addition to common cell biology and molecular biology techniques

Single Particle Tracking:

The mobility of individual molecule on the cell membrane reflects its association with cytoskeleton underneath the membrane. Such mobility of b2 integrin can be monitored by coupling single molecules with microbeads under 200 nm through specific antibodies. The beads are small enough so that only one or two integrin molecules can bind to them. Using the contrast enhancement method, the beads can be seen by light microscope, although their size falls below the theoretical resolution of light microscopy. Therefore, by tracking the movement of the beads, we can track movement of the integrin molecules. By analyzing the track, we can calculate the mobility of integrin and obtain its diffusion coefficient (D), which in turn reflects the cytoskeletal constraint on the membrane receptors.

 

Fluorescent Resonance Energy Transfer:

This method allows the detailed study of protein-protein interaction in living cells at real time to obtain temporal and spatial information. In this method, two interacting proteins are each labeled with different fluorophores. The emission wavelength of one (donor) fluorophore is the excitation wavelength of the other (acceptor). If the two proteins are close enough (50A), the excitation of the first fluorophore will result in the emission of the second fluorophore. This process, FRET, is highly sensitive to the distance (reciprocal to the R6, R = distance between two fluorophores) and orientation of two proteins (that carry the fluorophores). Therefore, FRET reflects the interaction of the two proteins.

Bibliography

Higher Education______________________________________________________________

 

1985-1990             Ph.D.         Biochemistry

                                                Department of Biochemistry

                                                City University of New York, New York

 

1985-1990             M.S           Biochemistry

                                                Department of Biochemistry

                                                City University of New York, New York

 

1985-1988             M.A.          Biochemistry          

                                                Department of Chemistry

                                                City College of New York, New York

 

1982-1985             M.S.          Biochemistry:         

                                                Department of Endocrinology

                                                Shanghai Institute of Biochemistry, Academia, Sinica

 

1978-1982             B.S.           Biology                  

                                                Department of Biology

                                                Wuhan University, China

 

 

Academic Appointments_______________________________________________________

 

2000-Present         Tenured Associate Professor, Department of Oral Biology, College of Dentistry, University of Illinois at Chicago

 

1998-Present         Associate Professor, Department of Oral Biology, College of Dentistry, University of Illinois at Chicago

 

1998-Present         Faculty of the Graduate College of the University of Illinois at Chicago

 

1994 - 1997          Assistant Professor, Department of Microbiology and Immunology, University of Tennessee, Memphis, College of Medicine

 

1994 - 1997          Faculty of the Graduate School of the University of Tennessee

 

1992 - 1994          Postdoctoral Fellow, Laboratory of Signal Transduction, The Rockefeller University.

 

1990 - 1992          Postdoctoral Associate, Laboratory of Cellular Physiology and Immunology, The Rockefeller University. 

 

 

Award________________________________________________________________________

 

      Recipient of Cancer Research Institute postdoctoral fellowship.

      Recipient of the Established Investigator Award, American Heart Association

 

 

Research Fundings_____________________________________________________________

 

NIH Grant:

 

1996-2001             NIGMS                                              RO1    P.I.                 

                                    Protein Kinase C-mediated Integrin activation

                             

2001-2006             NIGMS                                              RO1    P.I.                 

                                    Protein Kinase C-mediated Integrin activation

                 

2001-2005             American Heart Association                  Established Investigator             P.I.                              

                              Microtubule and Motor Proteins in

                              Integrin Activation                                                                    

 

1996-2005             The Council of Tobacco Research        Grant    P.I.                                                                        

                                Role of a C  Kinase Substrate in

                              Macrophage phagocytosis.

  

1994-1995             American Cancer Society                     Grant    P.I.                  

                              PKC substrates in the membrane

                              trafficking

 

      1994-1995             UT Medical Group Foundation Grant    P.I.                        

                                    Macrophage Phagocytosis

 

      1991-1994             Cancer Research Institute                     Fellowship                   

                                    Macrophage Activation

 

      1997-2000             American Heart Association                  Grant    P.I.                  

                                    Protein Kinase C-mediated

                                    Integrin Activation

                                    (Declined in favor of CTR grant)

 
Publications:__________________________________________________________________

 

Jianxun Li and Horst Schulz.  1988.  4-Bromo-2-octenoic acid specifically inactivates 3-ketoacyl-CoA thiolase and thereby fatty acid oxidation in rat liver mitochondria.  Biochemistry 27:5995-6000.

 

Tor Smeland, Jianxun Li, Chinhong Chu, Dean Cubas and Horst Schulz.  1989. The 3-hydroxyacyl-CoA epimerase activity of rat liver peroxisomes is due to the combined action of two enoyl-CoA hydratases.  Biochem. Biophys. Res. Commun. 160:988-992.

 

Jianxun Li, Tor E. Smeland and Horst Schulz.  1990.  D-3-Hydroxyacyl coenzyme A dehydratase from rat liver peroxisomes.  J. Biol. Chem. 265:13629-13634.

 

Jianxun Li, Daniel L. Norwood and Horst Schulz.  1990.  Mitochondrial metabolism of valproic acid.  Biochemistry 30:388-394.

 

Tor Smeland, Jianxun Li, Dean Cubas and Horst Schulz.  1991. New Development in Fatty Acid Oxidation. P.M. Coatf and K. Tanaka (eds).  Wiley-Liss.

 

Jianxun Li and Alan Aderem.  1992.  MacMARCKS, a novel member of the MARCKS family of protein kinase C substrates.  Cell 70:791-801.

 

Zixin Zhu, Zhihua Bao and Jianxun Li  1995.   MacMARCKS mutation blocks macrophage phagocytosis of zymosan.   J. Biol.Chem. 270:17652-17655

 

Jianxun Li, Zixin Zhu and Zhihua Bao 1996.  Role of MacMARCKS in integrin-dependent macrophage spreading and tyrosine phosphorylation of paxillin.  J. Biol.Chem.  271: 12985-12990

 

Lili Yue, Zhihua Bao and Jianxun Li.  1999.  MacMARCKS is an essential component in LFA-1 and ICAM-1 mediated leukocyte aggregation.  J. Cell. Physiol. 181, 355-360.

 

Lili Yue, Zhihua Bao and Jianxun Li.  2000. MacMARCKS restores the adhesion of Wehi 274.1.7 cells to the ICAM-1-coated surface. Cell Adhesion and Communication, 7(5). p355-366.

 

Ximing Zhou and Jianxun Li, 2000. MacMARCKS and Its Phosphorylation is Required for the Phorbol Ester-stimulated Diffusion of b2 Integrin Molecules. J. Biol. Chem, 275(26), p20217-20222

 

Lili Yue, Shijiang Lu, Jorge Garces, Tianquan Jin and Jianxun Li, 2000.  Protein Kinase C-regulated Dynamitin-MacMARCKS interaction is Involved in Macrophage Cell Spreading. J. Biol. Chem. 275(31), p23948-23956

 

Tianquan Jin, Lili Yue and Jianxun Li 2001. In Vivo Interaction between Dynamitin and MacMARCKS Detected by the Fluorescent Resonance Energy Transfer Method. J. Biol. Chem. 276(16), p12879-12884

 

Ximing Zhou and Jianxun Li, 2002. The microtubule cytoskeleton participates in control of beta(2) integrin avidity. J. Biol. Chem. 276 (48): 44762-44769

 

Tianquan Jin and Jianxun Li, 2002. Dynamitin Controls b2 Integrin Avidity by Modulating Cytoskeletal Constraint on Integrin Molecules. J. Biol. Chem. In press

 

Ximing Zhou, Tianquan Jin and Jianxun Li, 2002. The Signal Transduction Pathways Regulating the Cytoskeletal constraint on b2 Integrin through Ca2+, PKC and Calmodulin.

 

Hongying Zhen, Lili Yue and Jianxun Li, 2002. Biochemical Characterization of the ATPase Activity of Dynamitin.