AIF1(Allograft inflammatory factor 1), also known as IRT-1, is a protein that in humans is encoded by the AIF1 gene. This gene is induced by cytokines and interferon. Its protein product is thought to be involved in negative regulation of growth of vascular smooth muscle cells, which contributes to the anti-inflammatory response to vessel wall trauma. The gene expresses three transcripts.Using in vitro binding and coimmunoprecipitation assays, Autieri et al. (2003) determined that AIF1 interacts with actin. In unstimulated VSMCs, AIF1 colocalized with F-actin, but translocated to lamellipodia upon PDGF stimulation. VSMCs stably transduced with AIF1 retrovirus migrated 2.6-fold more rapidly in response to PDGF than control cells. AIF1 colocalized with RAC1, and AIF1-transduced VSMCs showed a constitutive and enhanced activation of RAC1. Autieri et al. (2003) concluded that AIF1 binds and polymerizes F-actin and regulates RAC1 activity and VSMC migration.