posted on 2024-01-22, 20:09authored byYunyoung Kim, W. Todd Miller
Erythropoietin-producing
hepatoma (Eph) receptors are a family
of tyrosine kinases that can act as tumor promoters or tumor suppressors,
depending on the receptor and cancer cell type. Cancer-associated
somatic mutations have been identified in all Eph receptors, but in
most cases, the functional effects of the mutations are unknown. In
this study, we expressed and purified the kinase domains of wild-type
(WT) EphA3 and EphB2 along with 16 cancer-associated mutants. We identified
mutations that decrease EphA3 activity and both activating and inhibitory
mutations in EphB2. To shed light on the mechanisms by which the mutations
altered kinase activity, we measured the thermal stabilities of the
enzymes and performed steady-state kinetic experiments. We also expressed
the full-length receptors in HEK293T cells to determine the cellular
effects. WT EphB2 promoted downstream ERK signaling, while a kinase-inactive
mutant (S706F) was similar to the control cells. In contrast, WT EphA3
(but not loss-of-function mutants) inhibited ERK signaling. The reciprocal
effects of EphB2 and EphA3 on ERK phosphorylation in HEK293T cells
were also evident in Ras-GTP loading. Thus, consistent with the dual
roles of Eph receptors as tumor promoters and tumor suppressors, somatic
mutations have the potential to increase or decrease Eph function,
resulting in changes in the downstream signaling transduction.