Stk40 deletion enhances c-Jun protein stability and compromises mesoderm differentiation

Serine/threonine kinase 40 (Stk40) was previously identified as a direct target gene of pluripotency-associated transcription factor Oct4 and its overexpression could facilitate differentiation of mouse embryonic stem cells (mESCs) towards the extraembryonic endoderm. Stk40-/- mice are lethal at the perinatal stage, displaying multiple organ failures. However, the molecular mechanisms underlying the physiological functions of Stk40 remain elusive. Here, we report that Stk40 ablation compromises the mesoderm differentiation from mESCs in vitro and in embryos. Mechanistically, Stk40 interacts with both mammalian constitutive photomorphogenic protein 1 (Cop1) and c-Jun, promoting degradation of c-Jun. Consequently, Stk40 knockout leads to c-Jun protein accumulation, which, in turn, might suppress the Wnt signaling activity and impair the mesoderm differentiation process. Overall, this study reveals that Stk40, together with Cop1, represent a novel axis for modulating c-Jun protein levels within an appropriate range during mesoderm differentiation from mESCs. Our finding provides new insight into the molecular mechanism regulating c-Jun protein stability and may have potential for managing related cellular disorders.