Figure 5.

(A and B) The GEF Sos, the adapter protein Grb2, and l-selectin associate upon stimulation via l-selectin in Jurkat or JCaM1.6+Lck cells. Association was revealed by co-immunoprecipitations and blotting Sos- or Grb2-IPs with anti-l-selectin or vice versa. No association of Sos, Grb2, and l-selectin was detected in JCaM1.6 cells. All blots were reprobed with the immunoprecipitating antibody (small panels). Non-specific IPs (n.s.) were performed with anti-CD20 as above. The blots are representative of three experiments. (C) Exchange activity in l-selectin IPs increases upon l-selectin triggering. l-selectin IPs were incubated with recombinant GDP. Ras and [³²P-α]-GTP. Increase in binding of [³²P-α]-GTP to Ras reflects exchange activity.