SOS1 and ischemia: Coimmunoprecipitation of SOS1 with EGFR antibody showed a significant increase of binding of SOS1 to EGFR after 2-hr ischemia in both core and penumbra areas in ischemic hemisphere as expected (Figure 3(a)), indicating that ischemia has a stimulatory (rather than inhibitory) effect on the interaction and SOS1 activity and that ischemia interferes with ERK1/2 phosphorylation at a site downstream of SOS1.