AIF-1 Is an Actin-Polymerizing and Rac1-Activating Protein That Promotes Vascular Smooth Muscle Cell Migration

Abstract

Abstract-Development of vascular restenosis is a multifaceted process characterized by migration and proliferation of vascular smooth muscle cells (VSMCs), resulting in loss of lumen diameter. Characterization of proteins that mediate this process is essential in our understanding of the pathogenesis of arterial injury. Allograft inflammatory factor-1 (AIF-1) is a cytoplasmic, calcium-binding protein that is expressed in VSMCs by allograft and balloon angioplasty injury. AIF-1 is not present in cultured human VSMCs but is induced by cytokines, and overexpression of AIF-1 results in increased VSMC growth and cell-cycle gene expression. To characterize AIF-1 modulatory effects in primary human VSMCs, AIF-1-interacting proteins were identified by an AIF-1/glutathione S transferase fusion protein affinity assay. MALDI-TOF mass spectrophotometric amino analysis identified actin as an AIF-1 interacting protein. This interaction was verified by coimmunoprecipitation. This is a functional interaction, because AIF-1 binds to and polymerizes F-actin in vitro. In unstimulated VSMCs, AIF-1 colocalizes with F-actin but translocates to lamellipodia on stimulation with platelet-derived growth factor. VSMCs stably transduced with AIF-1 retrovirus migrate 2.6-fold more rapidly (85.1Ϯ2.9 versus 225.5Ϯ16.6; PϽ0.001) in response to platelet-derived growth factor versus control cells. AIF-1 colocalizes with Rac1, and AIF-1-transduced VSMCs show a constitutive and enhanced activation of Rac1, providing a mechanism for the increased migration. These data indicate that AIF-1 binds and polymerizes F actin and also regulates Rac1 activity and VSMC migration. Considering the AIF-1 expression pattern in injured arteries, this suggests that AIF-1 may be involved in the cytoskeletal signaling network leading to vascular remodeling.

Overexpression of Allograft Inflammatory Factor-1 Promotes the Proliferation and Migration of Human Endothelial Cells (HUV-EC-C) Probably by Up-Regulation of Basic Fibroblast Growth Factor

“…1), whereas AIF-1 was negative in either the normal HUV-EC-C or the Vector-HUV-EC-C cells. This result is consistent with the studies by Autieri and us, demonstrating that AIF-1 was not expressed in the normal blood vessel (8,20).…”

Loss of Allograft Inflammatory Factor-1 Ameliorates Experimental Autoimmune Encephalomyelitis by Limiting Encephalitogenic CD4 T-Cell Expansion

“…Interestingly, the effect of Aif-1 deficiency on leukocyte populations after immunization was relatively modest, with a decrease of ~10% in the number of both CD3 the cytoplasm, and molecular functions ascribed to Aif-1 to date include actin bundling activity (35); it has also been linked to signaling via the small GTPase Rac (36,37), which itself is well known to affect actin cytoskeletal dynamics (38). The Aif-1 protein structure is notable for a conserved EF hand motif, although there are conflicting reports as to whether this is capable of binding Ca 2+ (39,40).…”

Cytokine expression and AIF-1-mediated activation of Rac2 in vascular smooth muscle cells: a role for Rac2 in VSMC activation

“…We have previously shown that AIF-1 is not expressed in unstimulated VSMC but is rapidly expressed in response to injury and inflammatory cytokines (1). Overexpression of AIF-1 in VSMC results in increased proliferation and cell cycle protein expression, increased migration, and activation of Rac1 (2,3).…”