Evidence for Eph kinases and ephrins on the surface of human
platelets. (A) Reverse transcription and
amplification (RT-PCR) of platelet RNA using primers specific for
EphB1, EphA4, ephrinA3, and ephrinB1. Platelet factor 4 (PF4) is
specific for platelets, whereas CD18 was used as a marker for leukocyte
contamination. Sequencing of the amplified products confirmed their
identities. (B) Immunoblots of total platelet lysates
with antibodies that recognize EphA4, EphB1, and ephrinB1.
(C) Platelets were incubated with 100 nM phorbol
12-myristate 13-acetate, allowed to adhere and spread on a
fibrinogen-coated surface, and then stained with FITC-conjugated,
His-6-tagged recombinant proteins corresponding to the exodomains of
EphA4, EphB1, and ephrinA4. Control proteins lacked residues required
for Eph/ephrin interactions are denoted with a “Δ.”