E3 ligase MKRN2 destabilizes PPP2CA proteins to inactivate canonical Wnt pathway and mitigates tumorigenesis of clear cell renal cell carcinoma.

Abstract

Background: Emerging evidence suggests that Makorin Ring Finger Proteins (MKRNs) are dysregulated in various human malignancies. However, the clinical and biological significance of MKRN2 in clear cell renal cell carcinoma (ccRCC) has been minimally explored. In this study, we investigated the exceptional role of MKRN2 in ccRCC. Methods: MKRN2 expression in ccRCC was analyzed with clinical samples and The Cancer Genome Atlas (TCGA) database. The proliferation and migration of cancer cells were assessed by transwell, colony formation, and wound healing assays. Gene expression, DNA methylation, and protein expression and ubiquitination were assessed by real-time PCR, bisulfite sequencing PCR, and western blotting assay, respectively. Protein interactions were verified by co-immunoprecipitation and immunofluorescence assays. In vivo experiments identified MKRN2 was a potential tumor inhibitor in ccRCC. Results: Down-regulation of MKRN2 was observed in human ccRCC tissues in both public databases and our clinical samples, mechanistically linked with its promoter DNA hypermethylation. Conversely, overexpression of MKRN2 was associated with ccRCC inhibition and favorable clinical outcomes. MKRN2 interacted with Protein Phosphatase 2 Catalytic Subunit Alpha (PPP2CA) and promoted k48-linked ubiquitination at its K41 residue, leading to the proteasomal degradation of PPP2CA proteins. Consequently, MKRN2-mediated PPP2CA repression increased β-catenin phosphorylation and decreased its protein levels, causing the inactivation of Wnt signaling pathway and amplification of apoptosis in ccRCC cells. Conclusions: This study demonstrated that the E3 ligase activity of MKRN2 had a pivotal role in regulating the PPP2CA-β-catenin-Wnt pathway and granted MKRN2 as a candidate tumor suppressor in ccRCC.