Regulation of p53 by the Ubiquitin-conjugating Enzymes UbcH5B/C in Vivo

Abstract

p53 levels are regulated by ubiquitination and 26 S proteasome-mediated degradation. p53 is a substrate for the E3 ligase Mdm2, however, the ubiquitin-conjugating enzymes (E2s) involved in p53 ubiquitination in intact cells have not been defined previously. To investigate the E2 specificity of Mdm2 we carried out an in vitro screen using a panel of ubiquitin E2s. Of the E2s tested only UbcH5A, -B, and -C and E2-25K support Mdm2-mediated ubiquitination of p53. The same E2s also support Mdm2 auto-ubiquitination. Small interfering RNA-mediated knockdown of UbcH5B/C causes accumulation of Mdm2 and p53 in unstressed cells. We show that suppression of UbcH5B/C inhibits p53 ubiquitination and degradation. Despite up-regulating the level of nuclear p53, UbcH5B/C knockdown does not on its own result in an increase in p53 transcriptional activity or sensitize p53 to activation by the therapeutic drugs doxorubicin and actinomycin D. We provide evidence that Mdm2 is responsible, at least in part, for repression of the transcriptional activity of the accumulated p53. In MCF7 cells levels of UbcH5B/C are reduced by doxorubicin and actinomycin D. This observation and the sensitivity of p53 expression to levels of UbcH5B/C raise the possibility that E2 regulation could be involved in signaling pathways that control the stability of p53. Our data indicate that UbcH5B/C are physiological E2s for Mdm2, which make a significant contribution to the maintenance of low levels of p53 and Mdm2 in unstressed cells and that inhibition of p53 ubiquitination and degradation by targeting UbcH5B/C is not sufficient to up-regulate p53 transcriptional activity.

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BibTeX RIS

BibTeX

@article{saville2026regulation,
  title = {{Regulation of p53 by the Ubiquitin-conjugating Enzymes UbcH5B/C in Vivo}},
  author = {Mark Saville and Alison Sparks and Dimitris Xirodimas and Julie Wardrop and Lauren Stevenson and Jean-Christophe Bourdon and Yvonne Woods and David Lane},
  journal = {Journal of Biological Chemistry},
  year = {2026},
  month = sep,
  doi = {10.1074/jbc.m403362200},
  url = {https://hal.science/hal-05751943v1},
  note = {CC BY},
}

RIS

TY  - JOUR
TI  - Regulation of p53 by the Ubiquitin-conjugating Enzymes UbcH5B/C in Vivo
AU  - Mark Saville
AU  - Alison Sparks
AU  - Dimitris Xirodimas
AU  - Julie Wardrop
AU  - Lauren Stevenson
AU  - Jean-Christophe Bourdon
AU  - Yvonne Woods
AU  - David Lane
PY  - 2026
DA  - 2026/09/16
JO  - Journal of Biological Chemistry
DO  - 10.1074/jbc.m403362200
UR  - https://hal.science/hal-05751943v1
AB  - p53 levels are regulated by ubiquitination and 26 S proteasome-mediated degradation. p53 is a substrate for the E3 ligase Mdm2, however, the ubiquitin-conjugating enzymes (E2s) involved in p53 ubiquitination in intact cells have not been defined previously. To investigate the E2 specificity of Mdm2 we carried out an in vitro screen using a panel of ubiquitin E2s. Of the E2s tested only UbcH5A, -B, and -C and E2-25K support Mdm2-mediated ubiquitination of p53. The same E2s also support Mdm2 auto-ubiquitination. Small interfering RNA-mediated knockdown of UbcH5B/C causes accumulation of Mdm2 and p53 in unstressed cells. We show that suppression of UbcH5B/C inhibits p53 ubiquitination and degradation. Despite up-regulating the level of nuclear p53, UbcH5B/C knockdown does not on its own result in an increase in p53 transcriptional activity or sensitize p53 to activation by the therapeutic drugs doxorubicin and actinomycin D. We provide evidence that Mdm2 is responsible, at least in part, for repression of the transcriptional activity of the accumulated p53. In MCF7 cells levels of UbcH5B/C are reduced by doxorubicin and actinomycin D. This observation and the sensitivity of p53 expression to levels of UbcH5B/C raise the possibility that E2 regulation could be involved in signaling pathways that control the stability of p53. Our data indicate that UbcH5B/C are physiological E2s for Mdm2, which make a significant contribution to the maintenance of low levels of p53 and Mdm2 in unstressed cells and that inhibition of p53 ubiquitination and degradation by targeting UbcH5B/C is not sufficient to up-regulate p53 transcriptional activity.
SN  - 0021-9258
SN  - 1083-351X
ER  -

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