The overall goal of this proposal is to understand how adhesion receptors of the immunoglobulin supergene family (IgSF) contribute to airway remodeling by affecting the function of airway smooth muscle cells. Vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) are members of the IgSF. Interactions of these receptors with their respective ligands, VLA-4 and LFA-1, are critical for the recruitment of eosinophil and T lymphocytes in the airway and in the development of airway hyperresponsiveness in animal models of airway hyperreactivity. Recent studies suggest that ICAM-1 and VCAM-1 may also have important """"""""outside-in"""""""" signaling functions, including mobilization of intracellular calcium, cytoskeletal rearrangement and chemokine secretion. Evidence from the applicant's laboratory shows that VCAM-1 engagement induces protein synthesis and activates phosphatilylinositol 3-kinase (PI3K) and p70 ribosomal S6 kinase (p70S6K). The goal of this proposal is to study the mechanisms of VCAM-1 and ICAM-1 signaling on human airway smooth muscle and to test the central hypothesis that engagement of these receptors induces smooth muscle hypertrophy. To test this hypothesis, in Aim 1 the applicant will determine the role of IgSF signaling in mediating smooth muscle hypertrophy by measuring incorporation of 3H-leucine, effects on smooth muscle cell-specific gene expression, and expression of cell cycle proteins.
In Aim 2, the applicant will determine whether IgSF-induced activation of PI3K and p70S6K modulates protein translation. Translation of a subset of mRNA characterized by a 5' terminal oligopyrimidine tract (5'TOP) will be compared in cells transfected with dominant negative PI3K or p70S6K cDNA.
In aim 3, the applicant will determine the mechanisms by which VCAM-1 induces activation of PI3K, by studying both receptor phosphorylation and the association with p120Cbl, and adapter protein known to activate PI3K. The applicant will also use cellular transfectants expressing mutant forms of VCAM-1 or Cbl to study the effect on PI3K activation and smooth muscle cell hypertrophy and hyperplasia. The direct interaction between myocytes and infiltrating leukocytes through cell adhesion molecules may have a profound effect on smooth muscle cell synthetic function, hypertrophy and proliferation. Understanding the mechanisms by which CAMs transduce signals that could induce myocyte activation may provide insight in new therapeutic measures to prevent airway inflammation and bronchial hyperreactivity.
