MERTK signaling in the retinal pigment epithelium regulates the tyrosine phosphorylation of GDP dissociation inhibitor alpha from the GDI/CHM family of RAB GTPase effectors.
Photoreceptor outer segments (OS) in the vertebrate retina undergo a process of continual renewal involving shedding of disc membranes that are cleared by phagocytic uptake into the retinal pigment epithelium (RPE). In dystrophic Royal College of Surgeons (RCS) rats, OS phagocytosis is blocked by a mutation in the gene encoding the receptor tyrosine kinase MERTK. To identify proteins tyrosine-phosphorylated downstream of MERTK in the RPE, MALDI-mass spectrometry with peptide-mass fingerprinting was used in comparative studies of RCS congenic and dystrophic rats. At times corresponding to peak phagocytic activity, the RAB GTPase effector GDP dissociation inhibitor alpha (GDI1) was found to undergo tyrosine phosphorylation only in congenic rats. In cryosections of native RPE/choroid, GDI1 colocalized with MERTK and the intracellular tyrosine-kinase SRC. In cultured RPE-J cells, and in transfected heterologous cells, MERTK stimulated SRC-mediated tyrosine phosphorylation of GDI1. In OS-fed RPE-J cells, GDI1 colocalized with MERTK and SRC on apparent phagosomes located near the apical membrane. In addition, both GDI1 and RAB5, a regulator of vesicular transport, colocalized with ingested OS. Taken together, these findings identify a novel role of MERTK signaling in membrane trafficking in the RPE that is likely to subserve mechanisms of phagosome formation.
Department of Biological Chemistry, University of Michigan Medical School, 1150 W. Medical Center Dr., Ann Arbor, MI 48109, USA; Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, 1000 Wall St., Ann Arbor, MI 48105, USA.
Shameka J
SJ
Shelby
Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, 1000 Wall St., Ann Arbor, MI 48105, USA.
Kecia L
KL
Feathers
Department of Biological Chemistry, University of Michigan Medical School, 1150 W. Medical Center Dr., Ann Arbor, MI 48109, USA.
Anna M
AM
Ganios
Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, 1000 Wall St., Ann Arbor, MI 48105, USA.
Lin
L
Jia
Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, 1000 Wall St., Ann Arbor, MI 48105, USA.
Jason M
JM
Miller
Department of Biological Chemistry, University of Michigan Medical School, 1150 W. Medical Center Dr., Ann Arbor, MI 48109, USA; Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, 1000 Wall St., Ann Arbor, MI 48105, USA. Electronic address: dathom@umich.edu.
Debra A
DA
Thompson
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D018929:Cell Culture Techniques; D019084:Fluorescent Antibody Technique, Indirect; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010449:Peptide Mapping; D010587:Phagocytosis; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051381:Rats; D011922:Rats, Mutant Strains; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D058499:Retinal Dystrophies / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism*; D000076202:c-Mer Tyrosine Kinase; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C513166:Chm protein, rat; C086796:GDP dissociation inhibitor 1; D020730:Guanine Nucleotide Dissociation Inhibitors; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; C490765:Mertk protein, rat; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase; D020691:rab GTP-Binding Proteins
Phagocytosis; RAB GTPase; Retinal dystrophy; Retinal pigment epithelium; Tyrosine phosphorylation