Transcription factor activation and protein phosphorylation patterns are distinct for CD28 and ICAM-1 co-stimulatory molecules.

We examined signaling differences between two co-stimulatory molecules, CD28 and ICAM-1 by analyzing transcription factors and proteins that are activated downstream of these co-stimulations. We observed that FAST-1, a crucial protein in the TGFβ signaling pathway, was activated by only ICAM-1 co-stimulation, and not by CD28. We also observed that receptor tyrosine kinases Csk, Dtk, FGFR1 and ROR2 were phosphorylated upon CD28 co-stimulation and IGF-1R, HGFR, MuSK and EphA8 were phosphorylated upon ICAM-1 co-stimulation. Together, these findings suggest that these two co-stimulators induce the activation of different sets of proteins, suggesting that each co-stimulatory molecule has its unique signaling profile.