DNA-dependent protein kinase (DNA-PK) has an important role in the repair of DNA damage and regulates the radiation sensitivity of glioblastoma cells. The VCP (valosine-containing protein), a chaperone protein that regulates ubiquitin-dependent protein degradation, is phosphorylated by DNA-PK and recruited to DNA double-strand break sites to regulate DNA damage repair. However, it is not clear whether VCP is involved in DNA-PKcs (DNA-PK catalytic subunit) degradation or whether it regulates the radiosensitivity of glioblastoma. Our data demonstrated that DNA-PKcs was ubiquitinated and bound to VCP. VCP knockdown resulted in the accumulation of the DNA-PKcs protein in glioblastoma cells, and the proteasome inhibitor MG132 synergised this increase. As expected, this increase promoted the efficiency of DNA repair in several glioblastoma cell lines; in turn, this enhanced activity decreased the radiation sensitivity and prolonged the survival fraction of glioblastoma cells in vitro. Moreover, the VCP knockdown in glioblastoma cells reduced the survival time of the xenografted mice with radiation treatment relative to the control xenografted glioblastoma mice. In addition, the VCP protein was also downregulated in ∼25% of GBM tissues from patients (WHO, grade IV astrocytoma), and the VCP protein level was correlated with patient survival (R2=0.5222, P<0.05). These findings demonstrated that VCP regulates DNA-PKcs degradation and increases the sensitivity of GBM cells to radiation.

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Jasmonates (JAs) are crucial to the coordination of plant stress responses and development. JA signaling depends on JASMONATE-ZIM DOMAIN (JAZ) proteins that are destroyed by the SCF COI1mediated 26S proteasome when the JAZ co-receptor COI1 binds active JA or the JA-mimicking phytotoxin coronatine (COR). JAZ degradation releases JAZ-interacting transcription factors that can execute stress and growth responses. The JAZ proteins typically contain Jas motifs that undergo conformational changes during JA signal transduction and that are important for the JAZ-COI1 interaction and JAZ protein degradation. However, how alterations in the Jas motif and, in particular, the JAZ degron part of the motif, influence protein stability and plant development have not been well explored. To clarify this issue, we performed bioassays and genetic experiments to uncover the function of the OsJAZ1 degron in rice JA signaling. We found that substitution or deletion of core segments of the degron altered the OsJAZ1-OsCOI1b interaction in a COR-dependent manner. We show that these altered interactions function as a regulator for JA signaling during flower and root development. Our study therefore expands our understanding of how the JAZ degron functions, and provides the means to change the sensitivity and specificity of JA signaling in rice.