Elucidation of a Eukaryotic Chemorepulsion Mechanism
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abstract
There is good evidence that some cells secrete chemorepellents that cause specific cell types to moveaway from them. However, much remains to be understood about the identity of the chemorepellents, theirreceptors, and the mechanisms they use to direct cell motility. We found that proliferating Dictyostelium cellssecrete a protein called AprA, and that AprA is an extracellular signal that functions as a chemorepellent.Although AprA has little sequence similarity to mammalian proteins, AprA has predicted structural similarity tothe human secreted dipeptidyl protease DPPIV, and shares functional properties with DPPIV. We found thathuman DPPIV is a chemorepellent for human and mouse neutrophils, and when applied locally, DPPIV caninduce neutrophils to leave a tissue in two mouse models of a lung disease called acute respiratory distresssyndrome (ARDS), and a mouse model of rheumatoid arthritis. To gain insights into a fundamental mechanismused in morphogenesis, ways to induce neutrophils to leave a tissue, and how one could augment or diminishthe effect of a chemorepellent, we propose three specific aims to elucidate the molecular mechanisms used byAprA and DPPIV to cause chemorepulsion. Aim 1 is to identify the AprA receptor, since this plays a key role inthe Dictyostelium chemorepulsion mechanism. Our preliminary work has identified a predicted G protein-coupled receptor called GrlH as a possible AprA receptor. We will carefully test this, and if GrlH is not thereceptor, we will use several approaches to identify the receptor. Aim 2 is to elucidate the AprAchemorepulsion signal transduction pathway. Our preliminary data indicate that some components of thechemorepulsion mechanism are different from components used by the chemoattraction mechanism thatallows Dictyostelium cells to aggregate toward cAMP. We will determine the extent to which thechemorepulsion mechanism uses known components of the chemoattraction mechanism, as well as use thepower of unbiased genetic screens in Dictyostelium to identify additional components of the chemorepulsionmechanism. Aim 3 is to test the hypothesis that DPPIV uses a G protein-coupled receptor called PAR2 toinduce neutrophil chemorepulsion, and use what we learn about the Dictyostelium chemorepulsion mechanismto determine the similarities and differences between the Dictyostelium and the human neutrophilchemorepulsion mechanisms. Together, this work combining molecular biology, genetics, cell biology, andbiochemistry will help to elucidate eukaryotic chemorepulsion mechanisms, and identify potential drug targetsthat could enhance or inhibit chemorepulsion.
