Over-expression of human UREB1 in colorectal cancer: HECT domain of human UREB1 inhibits the activity of tumor suppressor p53 protein

• Published in: Biochemical and biophysical research communications 2005-01, Vol.326 (1), p.7-17
• Main Authors: Yoon, Sun Young, Lee, Younghee, Kim, Joo Heon, Chung, An-Sik, Joo, Joung Hyuck, Kim, Chang-Nam, Kim, Nam-Soon, Choe, In Seong, Kim, Jae Wha
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Biomarkers, Tumor - genetics; Biomarkers, Tumor - metabolism; Cell Line, Tumor; Colorectal carcinoma; Colorectal Neoplasms - genetics; Colorectal Neoplasms - metabolism; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; E3 ubiquitin ligase; Enzyme Activation; Gene Expression Regulation, Neoplastic; Guanine Nucleotide Exchange Factors - chemistry; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - metabolism; HECT domain; Human UREB1; Humans; Molecular Sequence Data; Mutagenesis, Site-Directed; Over-expression; p53 destabilization; p53 transcriptional activity; Phosphoproteins - chemistry; Phosphoproteins - genetics; Phosphoproteins - metabolism; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Structure-Activity Relationship; Tumor Suppressor Protein p53 - genetics; Tumor Suppressor Protein p53 - metabolism; Ubiquitin-Protein Ligases
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2004.11.004

Many fundamental processes, including oncogenesis, have implicated HECT domain proteins with ubiquitin ligase activity. The protein human upstream regulatory element binding protein 1 (hUREB1) is a HECT domain protein whose function is not defined yet. Here, we investigate the function of hUREB1 as a ubiquitin–protein ligase in human colorectal cells. Ectopic expression of the HECT domain of hUREB1 reduces the protein level and transcriptional activity of the p53 tumor suppressor, which is abrogated by the deletion in the HECT domain or point mutations in the essential residues of the HECT domain. The ubiquitination and destabilization of p53 is observed in cells treated with the protease inhibitor MG132, implying that the HECT domain of hUREB1 suppresses the transcriptional activity of p53 through a ubiquitin-dependent degradation pathway. Based on the results of Northern blot analysis, RT-PCR, and immunohistochemical analyses, the over-expression of hUREB1 is associated with colorectal carcinoma. Moreover, protein levels of hUREB1 and p53 were inversely correlated. These findings suggest that hUREB1 can function, at least in part, as a negative regulator of p53 during the colorectal carcinoma progression through the ubiquitination pathway mediated by the HECT domain.