Quantitative Fret Studies of EphA2-Lyn Interactions.

The regulation of the receptor tyrosine kinase (RTK) signal transduction pathways is critical for proper cellular function. RTK activation occurs in response to ligand binding, which induces RTK dimerization or oligomerization to allow cross-phosphorylation of specific tyrosines in the kinase domains of the RTK. Downstream signals are then propagated upon the recruitment of soluble kinases or adaptor proteins to these phoshorylated tyrosines. The EphA2 receptor tyrosine kinase is a member of the largest RTK family and has been reported to initiate downstream signaling by recruiting Lyn, a member of the Src family of non-receptor tyrosine kinases. Contrary to expectations, quantitative FRET experiments demonstrate that ligand-induced EphA2 tyrosine phosphorylation does not lead to Lyn recruitment to EphA2. In control experiments, Lyn is efficiently recruited by a different RTK, EGFR, upon ligand stimulation. The differential interactions of Lyn with EphA2 and EGFR may be a means of signal diversification. Current work is focused on the mechanism behind the unexpected lack of interactions between EphA2 and Lyn upon EphA2 clustering and phosphorylation.