ARF-GEP100. a guanine nucleotide-exchange protein for ADP-ribosylation factor 6, involved in the apoptotic cell death of phagocytes
Akimasa SOMEYA1, Joel MOSS2, Martha Vaughan2, Isao NAGAOKA1
Abstract : ADP-ribosylation factors (ARFs) are 20-kDa GTP-binding proteins involved in the vesicular trafficking, the activation of phospholipase D and phosphatidylinositol 4-phosphate 5-kinase, and the modulation of phagocyte functions. Like other GTP-binding proteins, ARFs cycle between GTP-bound, active and GDP-bound, inactive status. Guanine nucleotide-exchange proteins (GEPs), which catalyze the change of bound GDP for GTP, are necessary for the activation of ARFs. Previously, we found a novel GEP with 100 kDa, named ARF-GEP100. In this study, we elucidated the role in ARF-GEP100 On phagocyte functions by transfection of ARF-GEP100. Overexpression of ARF-GEP100 induced apoptosis of mouse macrophage RAW264.7 cells and phorbol 12-myristate 13-acetate treated human monocyte U937 cells, which could be detected by morphological changes (nuclear condensation and formation of apoptotic bodies), annexin V-staining and TUNEL assay. ARF-GEP100-induced apoptosis was not inhibited by a caspase inhibitor zVAD-FMK. Furthermore, mutant analysis of ARF-GEP100 revealed that two regions (N- and C- termini) of ARF-GEP100 were essential for the induction of apoptosis, but the mutant defective in GDP-GTP exchange domain induced apoptosis. These results suggest that ARF-GEP100 induces apoptosis of monocytic phagocytes independent of both the caspase activation and GDP-GTP exchange activity.