Abstract 3108: A novel role for hPygo2 in ribosomal RNA transcription

• Published in: Cancer research (Chicago, Ill.) Ill.), 2013-04, Vol.73 (8_Supplement), p.3108-3108
• Main Authors: Andrews, Phillip G. P., Kao, Kenneth R.
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2013-3108

Background: Several ribosomes are required for each translated messenger RNA. During cell growth and division, a significant proportion of cellular resources are devoted to the production of ribosomes, but the epigenetic mechanisms by which cells adjust to this requirement are not fully understood. We have previously demonstrated that human Pygopus 2 (hPygo2) is highly expressed in, and required for the growth of a number of different cancers. hPygo2 functions as a chromatin remodeling protein through direct association with trimethylated Histone H3 at lysine4 (H3K4me3). It is here that hPygo2 likely serves as an adapter to which histone acetyltransferases can bind and promote further chromatin remodeling events required for transcription. We now present evidence that hPygo2 is involved in chromatin remodeling at the ribosomal (r)RNA promoter during proliferative growth of cancer cells. Methods: Immunoprecipitation (IP) and immunofluorescence (IF) was performed in breast (MCF7), ovarian (SKOV3) and cervical (HeLa) cancer cells. siRNAs were designed to specifically deplete hPygo2. For hPygo2 binding to the ribosomal gene promoter, chromatin IPs were used and analyzed by conventional or quantitative (q) PCR. 47S rRNA expression was measured by qPCR or by pulse-chase with either Br-UTP or 3H-uridine. Cell cycle analysis was performed by flow cytometry. Results: We found that hPygo2 interacted with UBF-1 and Treacle, two nucleolar proteins involved in 47S rRNA transcription. hPygo2 co-localized with UBF-1 and Treacle along with newly synthesized de novo rRNA in the nucleoli of cancer cells. hPygo2 was further detected at the ribosomal gene promoter along with core components of the rDNA transcription complex, including RNA polymerase I. Furthermore, hPygo2 was required for Histone H4 acetylation at the rRNA promoter and for transcription of the 47S pre-rRNA. Depletion of hPygo2 was accompanied by activation of the ribosomal stress response, detected by the binding of ribosomal protein L11 to hdm2, thereby inhibiting its E3 ubiquitin ligase activity resulting in p53 dependent growth arrest. Conclusion: Our results suggest that chromatin remodeling function of hPygo2 may serve to augment or maintain 47S pre-rRNA transcription required for ribosome biogenesis in cancer. Citation Format: Phillip G. P. Andrews, Kenneth R. Kao. A novel role for hPygo2 in ribosomal RNA transcription. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association