Abstracts (complete list) - Wissenschaft Online

Stephan Meinke, Philipp Eissmann, Carsten Watzl
Early events in NTB-A signaling
The activating receptor NTB-A belongs to the family of SLAM-related receptors and is
expressed on NK, T and B-cells. Engagement of NTB-A on human NK cells by homophilic
interaction with NTB-A expressing target cells can trigger cytotoxicity, cytokine
production and proliferation.
The crystal structure of the NTB-A homodimer has been solved recently. To confirm the
functional relevance of the interactions seen in the crystal, selected residues in the
binding region have been mutated. Cells transfected with the mutated receptors have
been used as targets of NK cells expressing wild type NTB-A in cytotoxicity assays.
Preliminary data show that the mutation of Histidine 54 or Serine 90 to Alanine reduces
the susceptibility to wt NTB-A mediated lysis, while changing Glutamine 88 to Alanine
does not.
Signal transduction via NTB-A is mediated by two immunoreceptor tyrosine-based
switch motifs (ITSM) in its cytoplasmic tail, which can bind the adapter molecules SLAMassociated
protein (SAP) and EWS-activated transcript 2 (EAT-2). To define the role of
these adapters in NTB-A signaling a stable knock down of SAP has been established in
NK cell lines. While 2B4 function was abolished in these cells, cytotoxicity against NTB-A
expressing target cells was not impaired upon SAP knock down. In agreement with the
functional data, western blotting experiments reveal no difference in NTB-A
phosphorylation between SAP knock down and control cells before and after receptor
engagement. These data suggest that the phosphorylation and function of NTB-A are
independent of SAP expression and imply a novel role of EAT-2 in the signal
transduction of NTB-A. To confirm these observations in a more physiological setting,
we are currently knocking down SAP expression in primary human NK cells.