Transcriptional and Posttranscriptional Down-Regulation of the Imprinted Tumor Suppressor Gene ARHI (DRAS3) in Ovarian Cancer

• Published in: Clinical cancer research Vol. 12; no. 8; pp. 2404 - 2413
• Main Authors: ZHEN LU, LUO, Robert Z, YINHUA YU, BAST, Robert C, HONGQI PENG, ROSEN, Daniel G, NEELY ATKINSON, E, WARNEKE, Carla, MAOSHENG HUANG, NISHMOTO, Arata, JINSONG LIU, LIAR, Warren S-L
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15-04-2006
• Subjects: Antineoplastic agents; ARHI; Base Sequence; Binding Sites - genetics; Biological and medical sciences; Cell Line, Tumor; Cells, Cultured; Down-Regulation - genetics; E2F Transcription Factors - genetics; E2F Transcription Factors - metabolism; Electrophoretic Mobility Shift Assay; Female; Female genital diseases; Gene Expression Regulation, Neoplastic; Genes, Tumor Suppressor; Genomic Imprinting; Gynecology. Andrology. Obstetrics; Humans; Luciferases - genetics; Luciferases - metabolism; Medical sciences; ovarian cancer; Ovarian Neoplasms - genetics; Ovarian Neoplasms - pathology; Pharmacology. Drug treatments; Promoter Regions, Genetic - genetics; Protein Binding; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; rho GTP-Binding Proteins - genetics; RNA instability; RNA Processing, Post-Transcriptional - genetics; RNA Stability; RNA, Messenger - genetics; RNA, Messenger - metabolism; Transcription, Genetic - genetics; transcriptional regulation; tumor suppressor gene; Tumors; Ovarian diseases; Transcription; Ovary cancer; Malignant tumor; Female genital diseases; Genomic imprinting; Tumor suppressor gene
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.CCR-05-1036

Purpose: ARHI expression is lost or markedly down-regulated in the majority of ovarian cancers. The mechanism by which ARHI is down-regulated
in ovarian cancers is still not clear. Our previous reports indicated that ARHI promoter activity was reduced in ovarian cancer
cells, due in part to the effects of negative regulatory transcription factor(s).
Experimental Design and Results: We now show that E2F1 and E2F4, but not E2F2, E2F3, or E2F5, bind to the ARHI promoter and repress its activity in ovarian cancer cells. Consistent with this observation, immunochemical staining of cell
lines and of 364 samples of ovarian cancer tissue show that the expression of E2F1 and E2F4 proteins is much higher in ovarian
cancer cells than in normal ovarian epithelial cells, and that increased expression of E2Fs was negatively correlated with
ARHI expression ( P < 0.05). Mutation of the putative E2F binding site in the ARHI promoter reversed this inhibitory effect and significantly increased ARHI promoter activity. In addition to the effects of transcriptional regulation, ARHI mRNA also exhibited a significantly reduced
half-life in ovarian cancer cells when compared with that in normal ovarian epithelial cells ( P < 0.01), suggesting posttranscriptional regulation of ARHI expression. ARHI mRNA contains AU-rich elements (ARE) in the 3′-untranslated
region. We have found that these AREs interact with HuR, an ARE-binding protein that stabilizes bound mRNAs, possibly contributing
to the rapid turnover of ARHI mRNA. Finally, reduced HuR ARE binding activity was observed in ovarian cancer cells when compared
with normal ovarian surface epithelium.
Conclusions: Taken together, our data suggest that ARHI expression is regulated at both the transcriptional and the posttranscriptional
levels, contributing to the dramatic decrease in ARHI expression in ovarian cancers.