Abstracts (complete list) - Wissenschaft Online

Abudula Abulizi, Annika Grabbe, Markus Brechmann, Christian Polaschegg, Nadine
Herrmann, Ingo Goldbeck, Kai Dittmann, Jürgen Wienands
SLP-65 signal transduction requires SH2-mediated membrane
anchoring and a kinase-independent adaptor function of Syk
The SH2 domain-containing leukocyte adaptor protein of 65 kDa (SLP-65) is a substrate
of activated tyrosine kinase Syk downstream of the B cell antigen receptor (BCR). A
main function of SLP-65 is to orchestrate the assembly of Ca 2+ -mobilizing enzymes at
the inner leaflet of the plasma membrane. However, the mechanism of SLP-65
membrane anchoring remains an enigma. We now employed two genetic reconstitution
systems to unravel structural requirements of SLP-65 for BCR-induced Ca 2+
mobilization and subsequent nuclear responses. First, mutational analysis of SLP-65 in
DT40 B cells revealed that its C-terminal SH2 domain controls efficient tyrosine
phosphorylation by the kinase Syk, plasma membrane recruitment, Ca 2+ flux as well as
subsequent NFAT activation for the initiation of gene transcription. Second, restoring
the Ca 2+ response in Jurkat T cell mutants with B cell signaling proteins uncovered a
kinase-independent adaptor function of Syk that is required for linking phosphorylated
SLP-65 to Ca 2+ mobilization. Hence, Syk is upstream as well as downstream of SLP-65.
Moreover, the mechanism by which SLP-65 translocates the Ca 2+ initiation complex to
the plasma membrane in B cells turned out to be fundamentally different to that utilized
by the closely related SLP-76 adaptor in activated T cells.