Differential TAM receptor-ligand-phospholipid interactions delimit differential TAM bioactivities

Elife. 2014 Sep 29;3:e03385. doi: 10.7554/eLife.03385.


The TAM receptor tyrosine kinases Tyro3, Axl, and Mer regulate key features of cellular physiology, yet the differential activities of the TAM ligands Gas6 and Protein S are poorly understood. We have used biochemical and genetic analyses to delineate the rules for TAM receptor-ligand engagement and find that the TAMs segregate into two groups based on ligand specificity, regulation by phosphatidylserine, and function. Tyro3 and Mer are activated by both ligands but only Gas6 activates Axl. Optimal TAM signaling requires coincident TAM ligand engagement of both its receptor and the phospholipid phosphatidylserine (PtdSer): Gas6 lacking its PtdSer-binding 'Gla domain' is significantly weakened as a Tyro3/Mer agonist and is inert as an Axl agonist, even though it binds to Axl with wild-type affinity. In two settings of TAM-dependent homeostatic phagocytosis, Mer plays a predominant role while Axl is dispensable, and activation of Mer by Protein S is sufficient to drive phagocytosis.

Keywords: Axl; Gas6; Mertk; Pros1; Tyro3; biochemistry; immunology; mouse; receptor tyrosine kinase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Marrow Cells / cytology
  • Bone Marrow Cells / drug effects
  • Bone Marrow Cells / metabolism
  • Cell Line
  • Embryo, Mammalian
  • Female
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism
  • Gene Expression Regulation
  • HEK293 Cells
  • Humans
  • Intercellular Signaling Peptides and Proteins / genetics
  • Intercellular Signaling Peptides and Proteins / metabolism*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Phagocytosis / genetics
  • Phosphatidylserines / metabolism*
  • Phosphatidylserines / pharmacology
  • Primary Cell Culture
  • Protein S / genetics
  • Protein S / metabolism*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Receptor Protein-Tyrosine Kinases / genetics
  • Receptor Protein-Tyrosine Kinases / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Signal Transduction
  • c-Mer Tyrosine Kinase


  • Intercellular Signaling Peptides and Proteins
  • Phosphatidylserines
  • Protein S
  • Proto-Oncogene Proteins
  • Recombinant Proteins
  • growth arrest-specific protein 6
  • Mertk protein, mouse
  • Receptor Protein-Tyrosine Kinases
  • Tyro3 protein, mouse
  • axl receptor tyrosine kinase
  • c-Mer Tyrosine Kinase