The Role of Talin‐1 and Kindlin‐3 in Neutrophilic Mac‐1 Activation

Abstract

Neutrophils rely on ß2 integrins, including Mac‐1, to mediate the cell to cell adhesions underlying trafficking events. Integrin mediated adhesiveness depends on ligand binding affinity, which is controlled through intracellular signaling pathways that induce conformational changes in the integrin extracellular domain in a process known as “inside‐out” signaling. In related integrins, binding of Talin‐1 and Kindlin‐3 to cytoplasmic integrin tails is required for these structural rearrangements. As Mac‐1 holds unique functions apart from other integrins, particularly in the etiology of autoimmune disease, the further characterization of Mac‐1 activation is key to gaining an understanding of how integrin affinity is regulated and ultimately how affinity changes promote autoimmune disease states. To investigate the role of Talin‐1 and Kindlin‐3, we employ functional assays and flow cytometry based reporter antibody assays to probe Mac‐1 conformation in human cell lines and transgenic mice. Preliminary studies suggest that in response to G‐protein coupled receptor signaling, both Talin‐1 and Kindlin‐3 are required for complete integrin activation. This contrasts with previous data that indicates Kindlin‐3 is dispensable for LFA‐1 ectodomain extension following P‐selectin glycoprotein ligand‐1 ligation, suggesting that the mechanisms of ß2 integrin activation may differ for divergent signaling pathways. Overall, determining a direct role for Talin‐1 and Kindlin‐3 in Mac‐1 activation may provide a clearer picture of the etiology of chronic inflammation while highlighting the specific structural confirmations that can be therapeutically targeted in order to stunt the severity of autoimmune states.