Dual roles for Prox1 in the regulation of the chicken betaB1-crystallin promoter.
OBJECTIVE
Lens fiber cell differentiation is marked by the onset of betaB1-crystallin expression and is controlled by the cooperative action of a set of transcription factors including Prox1, an atypical homeodomain protein. Previously, the authors reported that Prox1 directly interacts with the OL2 element found in the chicken betaB1-crystallin basal promoter to activate the expression of this gene. Here they mapped the location of activating and repressing sequences of the full-length chicken betaB1-crystallin promoter (-432/+30) in lens epithelial cells, annular pad cells, and intact lens and characterized Prox1-binding sites found in this region.


METHODS
Transfection analysis and transgenic mice were used to characterize upstream regions of the chicken betaB1-crystallin gene. DNaseI footprinting and chromatin immunoprecipitation was performed to identify Prox1-binding sites, and transfection analyses were used to characterize these sites functionally.


RESULTS
Sequences between -152 and -432 of the chicken betaB1-crystallin promoter mediated either promoter activation or repression, depending on the stage of lens differentiation tested. Two new Prox1-binding sites were found in this region that bound Prox1 more avidly than the OL2 element. However, neither binding site conferred Prox1-mediated activation on a heterologous promoter; instead, each allowed Prox1 to repress promoter function.


CONCLUSIONS
The function of the upstream region of the chicken betaB1-crystallin promoter changes depending on cellular context. These data suggest that Prox1 function as a transcriptional activator could be regulated at the DNA level based on the characteristics of the responsive elements.
Chen
Xiaoren
X
Department of Biological Sciences, University of Delaware, Newark, Delaware 19716, USA.
Taube
Jennifer R
JR
Simirskii
Vladimir I
VI
Patel
Tapan P
TP
Duncan
Melinda K
MK
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D016466:CHO Cells; D002642:Chick Embryo; D006224:Cricetinae; D003412:Cricetulus; D024202:Electrophoretic Mobility Shift Assay; D004847:Epithelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D018398:Homeodomain Proteins / Q000502:physiology*; D007908:Lens, Crystalline / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008958:Models, Molecular; D011401:Promoter Regions, Genetic; D011817:Rabbits; D012097:Repressor Proteins / Q000502:physiology*; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D038206:beta-Crystallin B Chain / Q000235:genetics*; D000098551:Prospero-Related Homeobox 1 Protein
D018398:Homeodomain Proteins; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; D038206:beta-Crystallin B Chain; D000098551:Prospero-Related Homeobox 1 Protein