A Single RET Mutation in Hirschsprung Disease Induces Intestinal Aganglionosis Via a Dominant-Negative Mechanism

Contrasting Effects of Cancer-Associated Mutations in EphA3 and EphB2 Kinases

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.

Pcgf1 gene disruption reveals primary involvement of epigenetic mechanism in neuronal subtype specification in the enteric nervous system

The enteric nervous system (ENS) regulates gut functions independently from the central nervous system (CNS) by its highly autonomic neural circuit that integrates diverse neuronal subtypes. Although several transcription factors are shown to be necessary for the generation of some enteric neuron subtypes, the mechanisms underlying neuronal subtype specification in the ENS remain elusive. In this study, we examined the biological function of Polycomb group RING finger protein 1 (PCGF1), one of the epigenetic modifiers, in the development and differentiation of the ENS by disrupting the Pcgf1 gene selectively in the autonomic-lineage cells. Although ENS precursor migration and enteric neurogenesis were largely unaffected, neuronal differentiation was impaired in the Pcgf1-deficient mice, with the numbers of neurons expressing somatostatin (Sst+ ) decreased in multiple gut regions. Notably, the decrease in Sst+ neurons was associated with the corresponding increase in calbindin+ neurons in the proximal colon. These findings suggest that neuronal subtype conversion may occur in the absence of PCGF1, and that epigenetic mechanism is primarily involved in specification of some enteric neuron subtypes.