Cytohesin-1 regulates fMLF-mediated activation and functions of the β2 integrin Mac-1 in human neutrophils

Abstract

The nucleotide exchange factor cytohesin-1 was previously reported to interact with the cytoplasmic domains of the integrin β-chain common to all β(2) integrins such as LFA-1 and Mac-1. We show here that cytohesin-1, which contributes to fMLF-induced functional responses in PMNs through activation of Arf6, restrains the activation of the β(2) integrin Mac-1 (αMβ(2)) in PMNs or dcAMP-differentiated PLB-985 cells. We found that the cytohesin-1 inhibitor SecinH3 or siRNA increased cell adhesion to immobilized fibrinogen and fMLF-mediated conformational changes of Mac-1, monitored using mAb CBRM1/5, specific for the activation epitope of the αM subunit. In contrast, PLB-985 cells overexpressing cytohesin-1 showed little adhesion to fibrinogen. The use of SecinH3 and siRNA also revealed that interference with cytohesin-1 signaling also enhanced phagocytosis of zymosan particles and chemotaxis toward fMLF in transwell migration assays. These increments of phagocytosis and chemotaxis in cells treated with SecinH3 and cytohesin-1 siRNA were reversed by a blocking mAb to the integrin-αM subunit. We provide evidence for increased polymerized cortical actin in cells treated with SecinH3 and that altered signaling through cytohesin-1 increased cell surface expression of FPRL-1 and impairs the late calcium mobilization response elicited by fMLF. The data provide evidence that stimulation with fMLF initiates a signaling cascade that restrains Mac-1 activation in PMNs. Such crosstalk between FPRL-1 and Mac-1 involves cytohesin-1. We suggest that cytohesin-1 may coordinate activation of the β(2) integrins to regulate PMN adhesion, phagocytosis, and chemotaxis.

Biophysical Description of Multiple Events Contributing Blood Leukocyte Arrest on Endothelium

“…The following conclusions were obtained:

A clear hierarchy of measured parameters was obtained: spreading could not be normal if durable arrest frequency was normal, and durable arrest could no be stimulated in patients’ cells if total arrests were lacking.

As expected, Mn ++ -induced arrests were normal in patients cells, validating the possibility of detecting individual interactions provided integrin unbending was correctly induced.

Total arrest frequency was normal, but durable arrest frequency was decreased in fMLF-stimulated neutrophils, confirming the importance of active cell functions to stabilize arrests in contrast with short-term molecular interactions (Pierres et al, 1994). This is consistent with the hypothesis that the integrin extension induced by fMLF (Diamond and Springer, 1993; El Azreq et al, 2011) might be obtained in absence of kindlin-3. It was not feasible to ascribe the arrest stabilization and spreading defects to incomplete integrin activation or defect of fMLF-induced clustering (Detmers et al, 1987).

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Cytohesin 1 regulates homing and engraftment of human hematopoietic stem and progenitor cells

“…19 Further studies have extended the role of cytohesins in regulating integrin functions to other cell types such as neutrophils and dendritic cells, and the precise adhesion-mediating effect of CYTH1 has been found to be highly context and cell-type dependent. [26][27][28] Our findings now extend the role of CYTH1 to HSPCs in addition to mature blood cells.…”

Function and mode of action of cytohesins in the epidermal growth factor pathway in colorectal cancer cells

“…Notably, the authors demonstrated that either amplification of ErbB2 or increased levels of the ErbB3/ErbB4 ligand heregulin led to de novo or acquired cetuximab resistance (18), and Ruan et al achieved similar results in a breast cancer study (19). Cytohesins, family members of GTPases, have been researched for their regulation of the reassembly of the cytoskeleton and the activation of integrin or the integrin signaling system, which is critically associated with cell adhesion and migration (11,20,21). A further study identified that cytohesins as EGFR activators may form a layer of positive regulation by facilitating the structural rearrangements required to convert the receptor dimer into its active conformation in lung cancer (10).…”