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LE Lerner, YE Gribanova, DB Farber; Interplay Between Members of the Sp Family of Transcription Factors Regulates the Expression of Rod-Specific cGMP-PDE Beta-subunit Gene . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3636.
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Purpose: Rod-specific cGMP-phosphodiesterase (cGMP-PDE) is the key effector enzyme that mediates signal transduction in rod photoreceptors of the vertebrate retina. Its catalytic ß-subunit (ß-PDE) is critical for the enzymatic activity. In addition, mutations in the ß-PDE gene cause severe retinal degenerations. Our goal has been to study the transcriptional mechanisms involved in the regulation of the ß-PDE gene expression. Detection of a G/C-rich activator response element (ß/GC) in the minimal rod-specific ß-PDE promoter prompted us to investigate the nuclear proteins involved in transcriptional regulation of the ß-PDE gene mediated through this control sequence. Methods: Transient transfections were carried out in 293 human embryonic kidney cells. Expression plasmids containing the full length Sp1, Sp3 or Sp4 cDNAs were co-transfected individually or in different combination along with the -93/+53 ß-PDE/luciferase reporter construct containing the ß/GC element. The level of luciferase activity was measured in cell lysates and normalized to the corresponding ß-galactosidase activity for each sample. Results: We have previously shown that both the ubiquitous Sp1 and the CNS-specific Sp4 transcription factors are expressed in the vertebrate retina and sequence-specifically interact with the ß/GC element. We now report that when transiently overexpressed in non-retinal 293 cells, the Sp4 transcription factor is able to significantly transactivate the -93/+53 minimal ß-PDE promoter. In contrast, the Sp1 transcription factor lacks such functional activity on this promoter. Another member of the Sp family, Sp3, did not show any ß-PDE promoter transactivation potential. In addition, Sp3 and to a lesser extent Sp1 repress the ß-PDE promoter transactivation produced by Sp4 in co-expression experiments. Conclusion: Our results suggest that interactions between different members of the Sp family of transcription factors including Sp1, Sp3 and Sp4 and the rod-specific minimal ß-PDE promoter may be implicated in transcriptional regulation of this gene.
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