Nck-interacting Ste20 kinase couples Eph receptors to c-Jun N-terminal kinase and integrin activation

The mammalian Ste20 kinase Nck-interacting kinase (NIK) specifically activa tes the c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase module. NIK also binds the SH3 domains of the SH2/SH3 adapter protein Nck. To determine whether Nck functions as an adapter to couple NIK to a recepto r tyrosine kinase signaling pathway, we determined whether NIK is activated by Eph receptors (EphR), EphRs constitute the largest family of receptor t yrosine kinases (RTK), and members of this family play important roles in p atterning of the nervous and vascular systems, In this report, we show that NIK kinase activity is specifically increased in cells stimulated by two E phRs, EphB1 and EphB2, EphB1 kinase activity and phosphorylation of a juxta membrane tyrosine (Y594), conserved in all Eph receptors, are both critical for NIK activation by EphB1, Although pY594 in the EphB1R has previously b een shown to bind the SH2 domain of Nck, we found that stimulation of EphB1 and EphB2 led predominantly to a complex between NIK/Nck, p62(dok), RasGAP , and an unidentified 145-kDa tyrosine-phosphorylated protein, Tyrosine-pho sphorylated p62(dok) most probably binds directly to the SH2 domain of Nck and RasGAP and indirectly to NIK bound to the SH3 domain of Nck. We found t hat NIK activation is also critical for coupling EphB1R to biological respo nses that include the activation of integrins and JNK by EphB1, Taken toget her, these findings support a model in which the recruitment of the Ste20 k inase NIK to phosphotyrosine-containing proteins by Nck is an important pro ximal step in the signaling cascade downstream of EphRs.