Annexin A1 (AnxA1) originating from mature neutrophils and their microparticles (MPs) plays an important anti‐inflammatory role during the resolution phase of inflammation. However, the role of AnxA1 during the process of granulocytic differentiation is still unknown. All‐trans retinoic acid (ATRA) can induce acute promyelocytic leukemic (APL) cells to differentiate along the granulocytic lineage and has been used successfully in treating APL patients. In this study, we investigated whether or not AnxA1 contributed to the anti‐inflammatory properties of ATRA‐treated APL (NB4; ATRA‐NB) cells using the transmigratory and adhesive assays. We found that ATRA was able to enhance the surface expression of AnxA1 and its receptor (FPR2/ALX) and the release of AnxA1‐containing MPs from ATRA‐NB4 cells, while the expression of annexin V was not elevated on the latter cells. Further studies demonstrated that exogenous AnxA1 could inhibit ATRA‐NB4 cells in their transmigratory activity and adhesion to endothelial cells. In addition, the transmigratory activity of ATRA‐NB4 cells can be significantly enhanced by pretreatment with a FPR2/ALX neutralizing antibody, suggesting that endogenous AnxA1 may contribute to the anti‐migratory effects. Finally, ATRA‐NB4‐derived MPs could also inhibit recipient cells in their transmigratory and adhesive activities and these anti‐inflammatory effects could be inhibited by pretreatment of MPs with a specific anti‐AnxA1 antibody. Flowcytometry studies further demonstrated that FITC‐labeled AnxA1 could be transported from MPs to the membrane of recipient ATRA‐NB4 cells. We conclude that biologically active AnxA1 may play a role in the anti‐inflammatory properties of ATRA‐treated APL cells during the process of granulocytic differentiation. J. Cell. Physiol. 227: 3661–3669, 2012. © 2012 Wiley Periodicals, Inc.

Annexin A1 (AnxA1) is an important anti-inflammatory mediator during granulocytic differentiation in all trans-retinoic acid (ATRA) treated acute promyelocytic leukemic (APL) cells. Dexamethasone has been used successfully to prevent complications in ATRA-treated APL patients, although its mechanism of action is still not clear. In the present study, we have examined the effect of dexamethasone on the modulation of AnxA1 in ATRA-APL NB4 (ATRA-NB4) cells, ATRA-NB4 cells-derived microparticles (MPs) and its role during cell-cell interaction between ATRA-NB4 cells and endothelial cells. Our results have shown that dexamethasone can inhibit the percentage of ATRA-NB4 cells expressing surface AnxA1 and its receptor FPR2/ALX in a time-dependent manner based on flow cytometric analysis. However, dexamethasone treatment of ATRA-NB4 cells has no significant effect on the level of AnxA1 mRNA, the total cellular level of AnxA1 protein or the release of AnxA1 from these cells, as determined by RT-PCR, Western blotting, and ELISA, respectively. Further studies demonstrate that dexamethasone is able to significantly inhibit the adhesion of ATRA-NB4 cells to endothelial cells, and this anti-adhesive effect can be inhibited if the cells were pre-treated with a neutralizing antibody specific for AnxA1. Finally, dexamethasone also enhances the release of AnxA1-containing MPs from ATRA-NB4 cells which can in turn prevent the adhesion of the ATRA-NB4 cells to endothelial cells. We conclude that biologically active AnxA1 originating from dexamethasone-treated ATRA-APL cells and their MPs plays an anti-adhesive effect and this contributes to inhibit the adhesion of ATRA-APL cell to endothelial cells.

Annexin A1 (AnxA1) originating from neutrophils and their microparticles (MPs) plays an important anti-inflammatory role. The role of AnxA1 during the process of granulocytic differentiation is still unknown. All-trans retinoic acid (ATRA) can induce differentiation of acute promyelocytic leukemic(APL) cells into mature granulocytes. We investigated whether or not AnxA1 contributed to the anti-inflammatory properties of ATRA-treated APL (NB4; ATRA-NB) cells. We found that ATRA was able to enhance the surface expression of AnxA1 and its receptor (FPR2/ALX) and the release of AnxA1-containing MPs from ATRA-NB4 cells. Further studies demonstrated that exogenous AnxA1 could inhibit ATRA-NB4 cells in their transmigratory and adhesive activity. In addition, the transmigratory activity of ATRA-NB4 cells can be significantly enhanced by pretreatment with a FPR2/ALX neutralizing antibody, suggesting that endogenous AnxA1 may contribute to the anti-migratory effects. Finally, ATRA-NB4-derived MPs could also inhibit recipient cells in their transmigratory and adhesive activities and these anti-inflammatory effects could be inhibited by pretreatment of MPs with an anti-AnxA1 antibody. Further studies demonstrated that FITC-labeled AnxA1 could be transport from MPs to the membrane of recipient ATRA-NB4 cells. We conclude that biologically active AnxA1 may play a role in the anti-inflammatory properties of ATRA-APL cells during the process of granulocytic differentiation.