%0 Journal Article
%T Arf Induction by Tgf¦Â Is Influenced by Sp1 and C/ebp¦Â in Opposing Directions
%A Yanbin Zheng
%A Caitlin Devitt
%A Jing Liu
%A Nida Iqbal
%A Stephen X. Skapek
%J PLOS ONE
%D 2013
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0070371
%X Recent studies show that Arf, a bona fide tumor suppressor, also plays an essential role during mouse eye development. Tgf¦Â is required for Arf promoter activation in developing mouse eyes, and its capacity to induce Arf depends on Smads 2/3 as well as p38 Mapk. Substantial delay between activation of these pathways and increased Arf transcription imply that changes in the binding of additional transcription factors help orchestrate changes in Arf expression. Focusing on proteins with putative DNA binding elements near the mouse Arf transcription start, we now show that Tgf¦Â induction of this gene correlated with decreased expression and DNA binding of C/ebp¦Â to the proximal Arf promoter. Ectopic expression of C/ebp¦Â in mouse embryo fibroblasts (MEFs) blocked Arf induction by Tgf¦Â. Although basal levels of Arf mRNA were increased by C/ebp¦Â loss in MEFs and in the developing eye, Tgf¦Â was still able to increase Arf, indicating that derepression was not the sole factor. Chromatin immunoprecipitation (ChIP) assay showed increased Sp1 binding to the Arf promotor at 24 and 48 hours after Tgf¦Â treatment, at which time points Arf expression was significantly induced by Tgf¦Â. Chemical inhibition of Sp1 and its knockdown by RNA interference blocked Arf induction by Tgf¦Â in MEFs. In summary, our results indicate that C/ebp¦Â and Sp1 are negative and positive Arf regulators that are influenced by Tgf¦Â.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070371