Study of the molecular mechanisms by which alpha4 beta1integrin promotes cell migration

Cell migration is vital for the life of many organisms from bacteria to humans. In humans, cell migration contributes to essential processes such as embryonic development, immune surveillance and tissue homeostasis, whereas deregulated cell migration can have pathological consequences, including cancer metastasis. The integrin family of cell surface adhesion receptors are critical for the attachment of cells to their extracellular matrix, an important step in the migration of many cell types. Among integrins, alpha4beta1 integrin has been shown to play a pivotal role in the migration of many cell types in vivo and to confer motility to cells in culture. My thesis work focuses on the study of the molecular mechanisms by which alpha4beta1 integrin regulates cell migration. In the first part of my thesis work, I and other people in the lab used Chinese hamster ovary (CHO) cells ectopically expressing the alpha4beta1 integrin to show that alpha4beta1 integrin is required and sufficient to promote directionally persistent cell migration in response to shear flow stimulation. This response was enhanced by disrupting paxillin binding to the alpha4 tail, while disrupting alpha4 phosphorylation provided evidence for this event in trailing tail detachment/retraction. When paxillin binding and alpha4 phosphorylation were both disrupted, the cells were unable to detach/retract their trailing edge and maintain stable cell polarity. Taken together, these results suggest that alpha4beta1 integrin promotes directionally persistent cell migration by facilitating both leading edge protrusions and trailing tail detachment/retraction, but it remains unclear as to how alpha4beta1 functions at the trailing edge and regulates directionally persistent cell migration.;The identification of novel protein interactions at the alpha4 integrin cytoplasmic tail (alpha4 tail) is crucial for the understanding of the molecular mechanisms behind alpha4beta1-promoted cell migration. In the second part of my thesis work, I identified and characterized a novel association between the alpha4 tail and non-muscle myosin IIA (MIIA). I showed that this association was not dependent on paxillin binding to the alpha4 tail or alpha4 phosphorylation, but was severely impaired by the double mutation. Furthermore, phosphorylation of synthetic alpha4 tail peptides inhibited a4 integrin/MIIA association, and increasing alpha4 phosphorylation correlated with a reduction in the association in vivo, showing that alpha4 phosphorylation can negatively regulate this association. In addition, alpha4beta1 integrin was able to recruit MIIA to ectopic sites in response to ligand binding, and alpha4 integrin and MIIA partially colocalized to the trailing edge of migrating cells. These results provide a basis for a novel mechanism in which the association between alpha4 integrin and MIIA may regulate trailing tail detachment/retraction and directionally persistent cell migration.;This thesis work provides new insights into the molecular mechanisms downstream of alpha4beta1 integrin that result in directionally persistent cell migration.