COP1 Functions as a Ubiquitin Ligase for PCDH9 Ubiquitination and Degradation

Abstract

Background: Constitutive photomorphogenic 1 (COP1, also known as RFWD2), a ring-finger-type E3 ubiquitin ligase, has been reported to play a pivotal role in the regulation of cell growth, apoptosis and DNA repair . Accumulating evidence has suggested that COP1 plays a role in tumorigenesis by triggering the ubiquitination and degradation of its substrates, but the potential mechanism remains unclear. Methods: We explored the interaction between COP1 and protocadherin 9 (PCDH9) by a yeast two-hybrid experiment. Coimmunoprecipitation (co-IP) assay and immunofluorescent staining were generated to investigate the interaction between and colocalization of COP1 and PCDH9. Western blotting and in vivo ubiquitination assay were performed to uncover the underlying mechanism of COP1 regulating PCDH9. Findings: COP1 was interacted and colocalized with PCDH9. In addition, COP1 acted as an E3 ligase to promote the ubiquitination and degradation of PCDH9 through the proteasome pathway in glioma cells. Furthermore, the type of COP1 mediated PCDH9 ubiquitination was Lys48-linked polyubiquitination. Finally, we found that the COP1 protein level was inversely correlated with the PCDH9 protein level in human glioma tissues. Interpretation: Our results suggest that COP1 is an E3 ubiquitin ligase for PCDH9 and reveal an important mechanism for PCDH9 regulation. Funding: This study was supported by the National Natural Science Foundation of China (81874081), the Young Science and Technology Innovation Team of Xuzhou Medical University (TD202006), the Foundation of Xuzhou Science and Technology Bureau (KC20139, KC20128, KC20091), the Jiangsu Provincial Qing Lan Project and Jiangsu Provincial Medical Youth Talent (QNRC2016784), and the Foundation of Jiangsu Provincial Health Department (M2020082). Declaration of Interest: None to declare. Ethical Approval: Our study was approved by the Research Ethics Committee of the Affiliated Hospital of Xuzhou Medical University. Written informed consent was obtained from every patient.