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Identification of two evolutionarily conserved genes regulating processing of engulfed apoptotic cells


Engulfment of apoptotic cells occurs throughout life in multicellular organisms. Impaired apoptotic cell clearance (due to defective recognition, internalization or degradation) results in autoimmune disease1,2. One fundamental challenge in understanding how defects in corpse removal translate into diseased states is the identification of critical components orchestrating the different stages of engulfment. Here we use genetic, cell biological and molecular studies in Caenorhabditis elegans and mammalian cells to identify SAND-1 and its partner CCZ-1 as new factors in corpse removal. In worms deficient in either sand-1 or ccz-1, apoptotic cells are internalized and the phagosomes recruit the small GTPase RAB-5 but fail to progress to the subsequent RAB-7(+) stage. The mammalian orthologues of SAND-1, namely Mon1a and Mon1b, were similarly required for phagosome maturation. Mechanistically, Mon1 interacts with GTP-bound Rab5, identifying Mon1 as a previously unrecognized Rab5 effector. Moreover, a Mon1–Ccz1 complex (but not either protein alone) could bind Rab7 and could also influence Rab7 activation, suggesting Mon1–Ccz1 as an important link in progression from the Rab5-positive stage to the Rab7-positive stage of phagosome maturation. Taken together, these data identify SAND-1 (Mon1) and CCZ-1 (Ccz1) as critical and evolutionarily conserved components regulating the processing of ingested apoptotic cell corpses.

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Figure 1: SAND-1 and CCZ-1 are required for the removal of apoptotic cell corpses in the adult hermaphrodite gonad.
Figure 2: Phagosomes are arrested at the RAB-5(+) stage in sand-1 mutant worms.
Figure 3: Mon1 is required for phagosome acidification and is recruited to phagosomes containing apoptotic cells.
Figure 4: A Mon1–Ccz1 complex is a Rab5 effector that links activated Rab5 to Rab7 recruitment and GDI displacement.


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We thank J. Casanova, C. Grimsley and members of the Ravichandran laboratory for helpful conversations; the Caenorhabditis Genetics Consortium (CGC) for nematode strains; A. Wandinger-Ness for Rab7 expression constructs; and J. Redick and S. Guillot of the Advanced Microscopy Facility for the preparation of specimens for electron microscopy. This work was supported by a post-doctoral fellowship via an NIH T32 Immunology Training Grant and American Heart Association Award (to J.M.K.), and grants from the NIGMS/NIH (to K.S.R.). K.S.R. is a William Benter Senior Fellow of the American Asthma Foundation.

Author Contributions J.M.K. performed all the experiments. J.M.K and K.S.R. planned and analysed the experimental results and wrote the manuscript.

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Correspondence to Jason M. Kinchen or Kodi S. Ravichandran.

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Kinchen, J., Ravichandran, K. Identification of two evolutionarily conserved genes regulating processing of engulfed apoptotic cells. Nature 464, 778–782 (2010).

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