Receptor tyrosine kinases, TYRO3, AXL, and MER, demonstrate distinct patterns and complex regulation of ligand-induced activation

J Biol Chem. 2014 Sep 12;289(37):25750-63. doi: 10.1074/jbc.M114.569020. Epub 2014 Jul 29.


TYRO3, AXL, and MER receptors (TAMs) are three homologous type I receptor-tyrosine kinases that are activated by endogenous ligands, protein S (PROS1) and growth arrest-specific gene 6 (GAS6). These ligands can either activate TAMs as soluble factors, or, in turn, opsonize phosphatidylserine (PS) on apoptotic cells (ACs) and serve as bridging molecules between ACs and TAMs. Abnormal expression and activation of TAMs have been implicated in promoting proliferation and survival of cancer cells, as well as in suppressing anti-tumor immunity. Despite the fact that TAM receptors share significant similarity, little is known about the specificity of interaction between TAM receptors and their ligands, particularly in the context of ACs, and about the functional diversity of TAM receptors. To study ligand-mediated activation of TAMs, we generated a series of reporter cell lines expressing chimeric TAM receptors. Using this system, we found that each TAM receptor has a unique pattern of interaction with and activation by GAS6 and PROS1, which is also differentially affected by the presence of ACs, PS-containing lipid vesicles and enveloped virus. We also demonstrated that γ-carboxylation of ligands is essential for the full activation of TAMs and that soluble immunoglobulin-like TAM domains act as specific ligand antagonists. These studies demonstrate that, despite their similarity, TYRO3, AXL, and MER are likely to perform distinct functions in both immunoregulation and the recognition and removal of ACs.

Keywords: AXL; Apoptosis; GAS6; MER; Phospholipid; Protein S; Receptor-tyrosine Kinase; Signal Transduction; TYRO3; Virus.

Publication types

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

MeSH terms

  • Apoptosis / genetics*
  • Blood Proteins / metabolism
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Intercellular Signaling Peptides and Proteins / metabolism
  • Jurkat Cells
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins / metabolism
  • Receptor Protein-Tyrosine Kinases / genetics*
  • Receptor Protein-Tyrosine Kinases / metabolism
  • Signal Transduction
  • Vesicular Stomatitis / genetics
  • c-Mer Tyrosine Kinase


  • Blood Proteins
  • Intercellular Signaling Peptides and Proteins
  • PROS1 protein, human
  • Proto-Oncogene Proteins
  • growth arrest-specific protein 6
  • MERTK protein, human
  • Receptor Protein-Tyrosine Kinases
  • TYRO3 protein, human
  • axl receptor tyrosine kinase
  • c-Mer Tyrosine Kinase