Tumor-associated antigen Prame targets tumor suppressor p14/ARF for degradation as the  receptor protein of CRL2(Prame) complex

Protein Preferentially Expressed Antigen in Melanoma (Prame), a tumor-associated antigen, has been found to frequently overexpress in various cancers, which indicates advanced cancer stages and poor clinical prognosis. Moreover, previous reports noted that Prame functions as a substrate recognizing receptor protein of Cullin RING E3 ligases (CRLs) to mediate potential substrates degradation through Ubiquitin Proteasome System (UPS). However, none of the Prame specific substrate has been identified so far. In this study, proteomic analysis of RBX1-interacting proteins revealed p14/ARF, a well-known tumor suppressor, as a novel ubiquitin target of RBX1. Subsequently, immunoprecipitation and in vivo ubiquitination assay determined Cullin2-RBX1-Transcription Elongation Factor B Subunit 2 (EloB) assembled CRL2 E3 ligase complex to regulate the ubiquitination and subsequent degradation of p14/ARF. Finally, through siRNA screening, Prame was identified as the specific receptor protein responsible for recognizing p14/ARF to be degraded. Additionally, via bioinformatics analysis of TCGA database and clinical samples, Prame was determined to overexpress in tumor tissues vs. paired adjacent tissues and associated with poor prognosis of cancer patients. As such, downregulation of Prame expression significantly restrained cancer cell growth by inducing G2/M phase cell cycle arrest, which could be rescued by simultaneously knocking down of p14/ARF. Altogether, targeting overexpressed Prame in cancer cells inactivated RBX1-Cullin2-EloB-Prame E3 ligase (CRL2(Prame)) and halted p14/ARF degradation to restrain tumor growth by inducing G2/M phase cell cycle arrest.