title: Requirement of adaptor protein GULP during stabilin-2-mediated cell corpse engulfment.
abstract: The prompt clearance of cells undergoing apoptosis is critical during embryonic development and normal tissue turnover, as well as during inflammation and autoimmune responses. We recently demonstrated that stabilin-2 is a phosphatidylserine receptor that mediates the clearance of apoptotic cells, thereby releasing the anti-inflammatory cytokine, transforming growth factor-beta. However, the downstream signaling components of stabilin-2-mediated phagocytosis are not known. Here, we provide evidence that the adaptor protein, GULP, physically and functionally interacts with the stabilin-2 cytoplasmic tail. Using fluorescent resonance energy transfer analysis and biochemical approaches, we show that GULP directly binds to the cytoplasmic tail of stabilin-2. Knockdown of endogenous GULP expression significantly decreased stabilin-2-mediated phagocytosis. Conversely, overexpression of GULP caused an increase in aged cell engulfment. The phosphotyrosine binding (PTB) domain of GULP was sufficient for the interaction with stabilin-2; therefore, transduction of TAT fusion PTB domain acts as a dominant negative, resulting in impaired engulfment of aged red blood cells in stabilin-2 expressing cells. In addition, the PTB domain of GULP was able to specifically interact with the NPXY motif of the stabilin-2 cytoplasmic tail. Taken together, these results indicate that GULP is a likely downstream molecule in the stabilin-2-mediated signaling pathway and plays an important role in stabilin-2-mediated phagocytosis.
authors.affiliation: Department of Biochemistry and Cell Biology, Cell and Matrix Research Institute, School of Medicine, Kyungpook National University, Daegu, 700-422, Korea.
authors.forename: Seung-Yoon
authors.initials: SY
authors.lastname: Park
authors.forename: Kae-Bok
authors.initials: KB
authors.lastname: Kang
authors.forename: Narendra
authors.initials: N
authors.lastname: Thapa
authors.forename: Sang-Yeob
authors.initials: SY
authors.lastname: Kim
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Lee
authors.forename: In-San
authors.initials: IS
authors.lastname: Kim
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D017209:Apoptosis; D016466:CHO Cells; D019556:COS Cells; D015816:Cell Adhesion Molecules, Neuronal / Q000502:physiology*; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004912:Erythrocytes / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D008954:Models, Biological; D011485:Protein Binding; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015816:Cell Adhesion Molecules, Neuronal; C454119:GULP1 protein, human; C449927:STAB2 protein, human