Inducible nucleosome depletion at OREBP-binding-sites by hypertonic stress.
BACKGROUND
Osmotic Response Element-Binding Protein (OREBP), also known as TonEBP or NFAT5, is a unique transcription factor. It is hitherto the only known mammalian transcription factor that regulates hypertonic stress-induced gene transcription. In addition, unlike other monomeric members of the NFAT family, OREBP exists as a homodimer and it is the only transcription factor known to bind naked DNA targets by complete encirclement in vitro. Nevertheless, how OREBP interacts with target DNA, also known as ORE/TonE, and how it elicits gene transcription in vivo, remains unknown.


METHODS
Using hypertonic induction of the aldose reductase (AR) gene activation as a model, we showed that OREs contained dynamic nucleosomes. Hypertonic stress induced a rapid and reversible loss of nucleosome(s) around the OREs. The loss of nucleosome(s) was found to be initiated by an OREBP-independent mechanism, but was significantly potentiated in the presence of OREBP. Furthermore, hypertonic induction of AR gene was associated with an OREBP-dependent hyperacetylation of histones that spanned the 5' upstream sequences and at least some exons of the gene. Nevertheless, nucleosome loss was not regulated by the acetylation status of histone.


CONCLUSIONS
Our findings offer novel insights into the mechanism of OREBP-dependent transcriptional regulation and provide a basis for understanding how histone eviction and transcription factor recruitment are coupled.
Tong
Edith H Y
EH
Department of Anatomical and Cellular Pathology, The Chinese University of Hong Kong, Hong Kong, China.
Guo
Jin-Jun
JJ
Xu
Song-Xiao
SX
Mak
Keri
K
Chung
Sookja K
SK
Chung
Stephen S M
SS
Huang
Ali-Long
AL
Ko
Ben C B
BC
D000107:Acetylation / Q000187:drug effects; D000449:Aldehyde Reductase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D006982:Hypertonic Solutions / Q000494:pharmacology*; D051379:Mice; D008836:Micrococcal Nuclease / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism*; D041681:NIH 3T3 Cells; D009707:Nucleosomes / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D020218:Response Elements / Q000235:genetics; D013312:Stress, Physiological / Q000187:drug effects*
D006657:Histones; D006982:Hypertonic Solutions; D050778:NFATC Transcription Factors; D009707:Nucleosomes; D000449:Aldehyde Reductase; D008836:Micrococcal Nuclease