Alpha4-beta1 integrin-mediated signal transduction in human leukocytes.

Cell adhesion plays a vital role in many cellular processes. Integrin receptors are a family of adhesion molecules that are composed of noncovalently linked $\alpha$ and $\beta$ subunits. $\beta1$ integrins expressed on the cell surface are involved in mediating interactions with the extracellular matrix and with other cells. Most cells in the body use $\beta1$ integrins to maintain tight adhesion and remain in a fixed location. However, cells of the immune system, which circulate through the body, must precisely regulate $\beta1$ integrin receptors from less adhesive to more adhesive states depending on the needs of the cell. In addition to acting as adhesion molecules, $\beta1$ integrins can transduce signals from the external environment to the interior of the cell. These signals may be critical for the cell to function properly. This thesis examines two aspects of $\beta1$ integrin-mediated signal transduction pathways in leukocytes. First, the structural requirements for $\beta1$-mediated tyrosine phosphorylation in a human T cell line were elucidated. A chimeric CD2/$\beta1$ receptor, composed of the $\beta1$ cytoplasmic domain and the extracellular and transmembrane portions of CD2, was employed to demonstrate that the $\beta1$ cytoplasmic domain is sufficient for increased tyrosine phosphorylation of three substrates, HEF1, pp105, and pp115. Analysis of $\beta1$ cytoplasmic domain truncations demonstrated that the five carboxy-terminal amino acids, KYEGK, were critical for the increased tyrosine phosphorylation of all three substrates. Second, the $\alpha4\beta1$ signaling cascade in a human monocytic cell line was explored. In the HL60 myelomonocytic cell line, $\alpha4\beta1$ engagement resulted in increased tyrosine phosphorylation of the Cbl adaptor protein and association of Cbl with the p85 subunit of phosphatidylinositol 3-kinase (PI 3-K). Subsequently, PI 3-K was activated, and $\alpha4\beta1$ stimulation also resulted in increased mitogen activated protein kinase (MAPK) activity. Inhibitor studies and expression of a dominant negative PI 3-K demonstrated that PI 3-K was required for $\alpha4\beta1$-stimulated MAPK activity. Furthermore, overexpression analyses revealed that the Cbl adaptor protein was a key component in the $\alpha4\beta1$ signaling pathway. Collectively, the results presented in this thesis expand our understanding of $\beta1$ integrin-mediated signal transduction.Ph.D.Applied SciencesBiological SciencesCellular biologyHealth and Environmental SciencesImmunologyMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130953/2/9825215.pd