title: Mer tyrosine kinase (MerTK) promotes macrophage survival following exposure to oxidative stress.
abstract: The MerTK plays several important roles in normal macrophage physiology, including regulation of cytokine secretion and clearance of apoptotic cells. Mer signaling in other cell types, including malignant cells that ectopically overexpress the RTK, leads to downstream prosurvival pathway activation. We explored the hypothesis that Mer has a prosurvival role in macrophages exposed to oxidative stress. H(2)O(2) treatment of peritoneal exudate murine macrophages and J774 cells rapidly stimulated Mer phosphorylation in a concentration-dependent manner. Mer phosphorylation was dependent on the ligand Gas6, as treatment with warfarin or MerFc (a fusion protein of the extracellular domain of Mer and the Fc portion of human Ig), inhibitors of Gas6 activity, blocked H(2)O(2)-mediated activation of Mer. Antiapoptotic signals including pAkt and pErk 1/2 were increased dramatically (threefold and 4.5-fold, respectively) in WT Mer-positive macrophages compared with Mer KO macrophages stimulated with H(2)O(2). In a consistent manner, Mer expression led to decreased cleavage of proapoptotic indicators PARP and Caspase-3. Furthermore, Mer provided up to twofold enhanced cellular survival to primary macrophages exposed to H(2)O(2). These data represent the first report of Mer activation in response to oxidative stress and demonstrate the ability of Mer RTK to promote macrophage survival in disease states that involve an oxidative stress environment.
authors.affiliation: Department of Pediatrics, University of Colorado Denver, Aurora, CO 80045, USA.
authors.forename: Adil
authors.initials: A
authors.lastname: Anwar
authors.forename: Amy K
authors.initials: AK
authors.lastname: Keating
authors.forename: David
authors.initials: D
authors.lastname: Joung
authors.forename: Susan
authors.initials: S
authors.lastname: Sather
authors.forename: Grace K
authors.initials: GK
authors.lastname: Kim
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Sawczyn
authors.forename: Luis
authors.initials: L
authors.lastname: Brandão
authors.forename: Peter M
authors.initials: PM
authors.lastname: Henson
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Graham
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D036341:Intercellular Signaling Peptides and Proteins / Q000502:physiology; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018384:Oxidative Stress; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology*; D000076202:c-Mer Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
chemical_list: D051017:Apoptosis Regulatory Proteins; D036341:Intercellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C490767:Mertk protein, mouse